physicsworld--2020-06-30--The secrets of success in electron and ion optics - Physics World

Vocation , collaboration and innovation provide a unifying frame of reference for the physicists and engineers of Kimball Physics , a New Hampshire-based technology company that specializes in the design and manufacture of precision electron sources , electron optics and ultrahigh-vacuum ( UHV ) chambers and components .
That frame of reference , it seems , is as solid today as it was 50 years ago , when physics professor Chuck Crawford spun Kimball Physics out from his research programme at Massachusetts Institute of Technology ( MIT ) .
Consistency matters to Crawford , which is why the goal back @ @ @ @ @ @ @ today : “ To advance humankind by doing good physics – specifically electron optics and vacuum physics – and all the while growing , being good citizens , making a living , and having fun.
” Context aside , Crawford ’ s commercial vision was to identify an opportunity to advance the field of UHV electron and ion optics , and specifically the niche where Kimball Physics could add most value for a range of customers – from university researchers and US national laboratories to multinational “ big-science ” facilities and semiconductor industry @ @ @ @ @ @ @ Physics has carved out – and subsequently scaled – its specialist niche to encompass the design and manufacture of electron optical equipment for the semiconductor industry ; electron sources for electron microscopes and electron lithography ; as well as custom high-brightness sources and related technologies for free-electron lasers , particle accelerators and X-ray systems .
That custom offering includes a mix of products tailored for the exacting requirements of the space industry as well as specialist Multi CF vacuum chambers for “ cold physics ” research and other exotic physics experiments .
Remarkably @ @ @ @ @ @ @ , Crawford remains engaged with the operations at Kimball Physics .
“ Chuck is still in regular communication and I doubt he will ever stop thinking up new ideas , ” explains Abigail LePage , a physicist and Kimball Physics ’ president and chief executive officer .
“ He doesn ’ t consider what he does as work .
He ’ s having fun and that mindset informs the collective culture here at Kimball Physics.
” That culture is further defined by “ open-book management ” , a non-hierarchical working model that seeks @ @ @ @ @ @ @ as partners in the business .
Transparency is the key , ensuring Kimball Physics ’ teams have a holistic view of the company ’ s financial metrics – revenue , profit , cash flow , capital expenditure and the like – so that they can make informed decisions to drive operational and strategic priorities .
That trust in the workforce yields significant gains – and not just commercially .
“ Many of our staff see what they do as more of a vocation , ” claims David Altobelli , senior scientist at Kimball @ @ @ @ @ @ @ of pride in their work and pushing the technology forward.
” If vocation underpins the work ethic among Kimball Physics ’ scientists and engineers , the vendor ’ s overarching commercial drivers are shaped by a collective focus on new product innovation and an open , inclusive dialogue with customers large and small .
“ Innovation at Kimball Physics is all about assimilation , ” says Altobelli .
“ Tracking the pulse of the market requires close collaboration with scientific and industry customers to ensure that our product development aligns with their research @ @ @ @ @ @ @ about 30 % of the products that Kimball Physics ships each year are custom-made to users ’ bespoke technical requirements .
“ We ’ re motivated by the challenging problems and opportunities that we see in the custom business , ” Altobelli adds .
“ After all , today ’ s one-off product , for a single end-user , can evolve into tomorrow ’ s standard product for many.
” Unsurprisingly , Kimball Physics is active along many R & D coordinates – in each case working closely with customers .
NASA is @ @ @ @ @ @ @ 10 years ago , well before additive manufacturing became a mainstream technology , the vendor teamed up with colleagues at the US space agency to build a platform for electron-beam free-form fabrication – an innovation that may ultimately enable additive manufacturing in space .
Other NASA projects involve laboratory testing and characterization of satellite shielding materials – essentially using electron and ion sources to simulate the solar wind that a craft will experience – as well as specific product innovations to minimize power consumption and footprint ( e.g .
delivering a 50 μA @ @ @ @ @ @ @ < 100 mW ) .
“ We do take risks – within reason – and are prepared to back projects that some vendors would walk away from , ” explains LePage , citing Kimball Physics ’ work on the optics for novel electron sources such as superconducting quantum dots , cold electron sources and laser-excited emitters .
“ These more speculative plays are crucial in loading our toolbox for future product innovations , ” she adds .
Another promising commercial opportunity is ultrafast electron microscopy , with Kimball Physics supplying electron sources and @ @ @ @ @ @ @ new generation of microscopes that offer temporal resolutions in the sub-nanosecond regime for single-shot applications ( with up to 10 million electrons/pulse ) and into the deep femtosecond range for stroboscopic applications ( with thousands of electrons/pulse ) .
Elsewhere , the firm ’ s Multi CF UHV chambers and associated hardware – “ the result of inadequately supervised physicists running amuck with CNC machines ” , according to Crawford – provide a core enabling technology in cold-atom physics experiments , where accuracy of port alignment is critical for optimal laser access .
@ @ @ @ @ @ @ Cold Atom Lab , for example , has seen the Kimball Physics Multi-CF “ mini ” cube UHV chamber deployed on the International Space Station to support such studies .
Other Multi CF applications include electron gun and ion source housings ; detector housings and subsystems ; as well as portable , low-cost UHV chambers .
“ Our Multi CF chambers enable UHV operation with enhanced capabilities – more of a ‘ value-added ’ system or instrument housing than just an evacuated environment , ” claims Altobelli .
What he ’ s referring @ @ @ @ @ @ @ CF sizes and configurations , featuring precise geometries for optimized internal access , highly polished surfaces , contoured interiors and minimal welds , and annular grooves around most ports to allow mounting of internal hardware and devices .
Equally , while most of the standard Multi CF chambers and fittings are made from monolithic structures of 316L stainless steel , customized options are also available in titanium for more demanding technical requirements ( such as reduction of hydrogen outgassing , local magnetic effects and weight ) .
Looking ahead , a significant chunk @ @ @ @ @ @ @ D effort will focus on realizing next-generation electron sources and optimized optics to address the already large ( and growing ) markets for electron-beam inspection , metrology and electron lithography within the semiconductor industry .
“ Electron emitters with precision optics are our dominant product line and key for our future product innovation , ” notes LePage .
Of more immediate concern to LePage and colleagues is mapping a course through the current Covid-19 disruption , ensuring Kimball Physics continues to remain on a firm footing as it looks to the next 50 @ @ @ @ @ @ @ of being an innovative and solid high-tech company , ” she concludes , “ and we don ’ t intend to let the pandemic change that .
”

Customer-centric innovation is helping US manufacturer Kimball Physics to prosper in its specialist niche of ultrahigh-vacuum electron and ion optics
Eyeing the horizon: Kimball Physics is active along many R&D coordinates – in each case working closely with its customers. (Courtesy: Kimball Physics)
Vocation, collaboration and innovation provide a unifying frame of reference for the physicists and engineers of Kimball Physics, a New Hampshire-based technology company that specializes in the design and manufacture of precision electron sources, electron optics and ultrahigh-vacuum (UHV) chambers and components. That frame of reference, it seems, is as solid today as it was 50 years ago, when physics professor Chuck Crawford spun Kimball Physics out from his research programme at Massachusetts Institute of Technology (MIT).
Consistency matters to Crawford, which is why the goal back then remains the mission at Kimball Physics today: “To advance humankind by doing good physics – specifically electron optics and vacuum physics – and all the while growing, being good citizens, making a living, and having fun.” Context aside, Crawford’s commercial vision was to identify an opportunity to advance the field of UHV electron and ion optics, and specifically the niche where Kimball Physics could add most value for a range of customers – from university researchers and US national laboratories to multinational “big-science” facilities and semiconductor industry OEMs.
On that canvas, Kimball Physics has carved out – and subsequently scaled – its specialist niche to encompass the design and manufacture of electron optical equipment for the semiconductor industry; electron sources for electron microscopes and electron lithography; as well as custom high-brightness sources and related technologies for free-electron lasers, particle accelerators and X-ray systems. That custom offering includes a mix of products tailored for the exacting requirements of the space industry as well as specialist Multi CF vacuum chambers for “cold physics” research and other exotic physics experiments.
Employee focus meets customer focus
Remarkably, five decades after starting the business, Crawford remains engaged with the operations at Kimball Physics. “Chuck is still in regular communication and I doubt he will ever stop thinking up new ideas,” explains Abigail LePage, a physicist and Kimball Physics’ president and chief executive officer. “He doesn’t consider what he does as work. He’s having fun and that mindset informs the collective culture here at Kimball Physics.”
That culture is further defined by “open-book management”, a non-hierarchical working model that seeks to empower all staff by treating them as partners in the business. Transparency is the key, ensuring Kimball Physics’ teams have a holistic view of the company’s financial metrics – revenue, profit, cash flow, capital expenditure and the like – so that they can make informed decisions to drive operational and strategic priorities.
That trust in the workforce yields significant gains – and not just commercially. “Many of our staff see what they do as more of a vocation,” claims David Altobelli, senior scientist at Kimball Physics. “Everybody takes a lot of pride in their work and pushing the technology forward.”
“No” is not an option for physicists when an important project must move forward. Necessity is the driver of innovation David Altobelli, senior scientist at Kimball Physics
If vocation underpins the work ethic among Kimball Physics’ scientists and engineers, the vendor’s overarching commercial drivers are shaped by a collective focus on new product innovation and an open, inclusive dialogue with customers large and small. “Innovation at Kimball Physics is all about assimilation,” says Altobelli. “Tracking the pulse of the market requires close collaboration with scientific and industry customers to ensure that our product development aligns with their research and commercial priorities.”
Abigail LePage: “We’re proud of being an innovative and solid high-tech company.” (Courtesy: Kimball Physics)
As such, about 30% of the products that Kimball Physics ships each year are custom-made to users’ bespoke technical requirements. “We’re motivated by the challenging problems and opportunities that we see in the custom business,” Altobelli adds. “After all, today’s one-off product, for a single end-user, can evolve into tomorrow’s standard product for many.”
Unsurprisingly, Kimball Physics is active along many R&D coordinates – in each case working closely with customers. NASA is a case in point. More than 10 years ago, well before additive manufacturing became a mainstream technology, the vendor teamed up with colleagues at the US space agency to build a platform for electron-beam free-form fabrication – an innovation that may ultimately enable additive manufacturing in space. Other NASA projects involve laboratory testing and characterization of satellite shielding materials – essentially using electron and ion sources to simulate the solar wind that a craft will experience – as well as specific product innovations to minimize power consumption and footprint (e.g. delivering a 50 μA electron-beam source for satellite positioning that consumes <100 mW).
“We do take risks – within reason – and are prepared to back projects that some vendors would walk away from,” explains LePage, citing Kimball Physics’ work on the optics for novel electron sources such as superconducting quantum dots, cold electron sources and laser-excited emitters. “These more speculative plays are crucial in loading our toolbox for future product innovations,” she adds.
High-value vacuum innovation
Another promising commercial opportunity is ultrafast electron microscopy, with Kimball Physics supplying electron sources and column optics to research groups for a new generation of microscopes that offer temporal resolutions in the sub-nanosecond regime for single-shot applications (with up to 10 million electrons/pulse) and into the deep femtosecond range for stroboscopic applications (with thousands of electrons/pulse).
Elsewhere, the firm’s Multi CF UHV chambers and associated hardware – “the result of inadequately supervised physicists running amuck with CNC machines”, according to Crawford – provide a core enabling technology in cold-atom physics experiments, where accuracy of port alignment is critical for optimal laser access. A high-profile collaboration with NASA’s Cold Atom Lab, for example, has seen the Kimball Physics Multi-CF “mini” cube UHV chamber deployed on the International Space Station to support such studies. Other Multi CF applications include electron gun and ion source housings; detector housings and subsystems; as well as portable, low-cost UHV chambers.
“Our Multi CF chambers enable UHV operation with enhanced capabilities – more of a ‘value-added’ system or instrument housing than just an evacuated environment,” claims Altobelli. What he’s referring to is an array of unique Multi CF sizes and configurations, featuring precise geometries for optimized internal access, highly polished surfaces, contoured interiors and minimal welds, and annular grooves around most ports to allow mounting of internal hardware and devices. Equally, while most of the standard Multi CF chambers and fittings are made from monolithic structures of 316L stainless steel, customized options are also available in titanium for more demanding technical requirements (such as reduction of hydrogen outgassing, local magnetic effects and weight).
Looking ahead, a significant chunk of Kimball Physics’ long-range R&D effort will focus on realizing next-generation electron sources and optimized optics to address the already large (and growing) markets for electron-beam inspection, metrology and electron lithography within the semiconductor industry. “Electron emitters with precision optics are our dominant product line and key for our future product innovation,” notes LePage.
Of more immediate concern to LePage and colleagues is mapping a course through the current Covid-19 disruption, ensuring Kimball Physics continues to remain on a firm footing as it looks to the next 50 years. “We’re proud of being an innovative and solid high-tech company,” she concludes, “and we don’t intend to let the pandemic change that.”


physicsworld--2020-06-30--Radiation alters ceramic grain boundaries - Physics World

Grain boundaries in ceramics may not be as chemically stable as previously thought .
So say researchers at the University of Wisconsin-Madison in the US who have found that carbon atoms collect or segregate at the boundaries of silicon carbide – a technologically important ceramic – when the material is exposed to ionizing radiation .
The result could help improve our understanding of ceramics in general and aid the development of better ceramic materials for applications in nuclear energy .
Changes in the chemical composition of grain boundaries – the interface between two different grains in a polycrystalline material – @ @ @ @ @ @ @ mechanical strength , corrosion resistance and radiation tolerance .
This is because the boundaries act as traps for defects , sites for corrosion reactions and channels for diffusing other chemicals through the material .
Radiation-induced segregation is a well-known phenomenon in metal alloys .
When such alloys are irradiated , the bombardment of neutrons , ions and other particles creates defects .
More specifically , defects known as Frenkel pairs form when an atom leaves its place in the crystal lattice ( creating a vacancy ) and lodges in a nearby location ( @ @ @ @ @ @ @ can then either recombine with each other or migrate to defect traps such as grain boundaries .
If different types of atoms in the alloy move at different rates , certain elements build up or become depleted in the vicinity of the boundaries .
Because ceramics have stronger interatomic bonds than metals , researchers had long assumed that the atoms in ceramics were not subject to this type of segregation .
Now , however , a team of researchers led by Izabela Szlufarska has turned this idea on its head by studying the @ @ @ @ @ @ @ ( SiC ) .
This ceramic is employed in nuclear energy and jet engines , among other high-tech applications , and it also shows promise for advanced nuclear reactors and microelectrochemical systems operating in harsh conditions .
Szlufarska and colleagues found that the material ’ s grain boundaries became enriched with carbon atoms when they bombarded it with ions at a temperature of 300°C .
At this temperature , which is much lower than is required to initiate radiation-induced segregation in metals , they found that the radiation dislodged some carbon atoms from @ @ @ @ @ @ @ in metals , the resulting pair of defects in the SiC included a vacancy site and an interstitial ( in this case , a loosely-bound carbon atom ) .
They also observed that these untethered interstitials migrated towards the grain boundaries , where they accumulated , changing the material ’ s chemistry .
The degree of segregation diminished when they irradiated the material at 600°C .
The researchers obtained their result by analysing the chemical composition of grain boundaries in pristine samples of SiC grown by chemical vapour deposition using the latest scanning @ @ @ @ @ @ @ and Oak Ridge National Laboratory .
They say that the phenomenon is likely to occur in other polycrystalline ceramics , too , and they also note that the segregation might be turned into an advantage , by making it possible to produce new types of ceramic materials with improved properties .
“ The radiation might in fact be used as a tool to fine-tune grain boundary chemistry , ” explains study co-author Xing Wang .
However , the researchers , who report their findings in Nature Materials , also note that the much @ @ @ @ @ @ @ suggest that our understanding of radiation-induced segregation in metals may not transfer directly to ceramics .
“ Unlike metal alloys , ceramics have much more complex energy landscapes for defect reactions and multiple sublattices in which defects can migrate , ” they say .
To explore this landscape , the team developed an ab initio informed rate theory model that reproduces and explains the low-temperature radiation-induced segregation behaviour in SiC .
These calculations also suggest that carbon segregation near grain boundaries in SiC comes about due to two factors : the different diffusivities @ @ @ @ @ @ @ the different reaction energy barriers between silicon and carbon sublattices in the material .
In their future studies , Szlufarska and colleagues plan to study how radiation-induced segregation in SiC depends on other conditions – for example , the total dose of radiation .
They will also investigate different types of grain boundaries .

Silicon carbide after irradiation, in which loose carbon atoms (green) move toward the boundary (dashed line) between grains of the crystalline ceramic. Courtesy: Hongliang Zhang
Grain boundaries in ceramics may not be as chemically stable as previously thought. So say researchers at the University of Wisconsin-Madison in the US who have found that carbon atoms collect or segregate at the boundaries of silicon carbide – a technologically important ceramic – when the material is exposed to ionizing radiation. The result could help improve our understanding of ceramics in general and aid the development of better ceramic materials for applications in nuclear energy.
Changes in the chemical composition of grain boundaries – the interface between two different grains in a polycrystalline material – can dramatically affect a material’s mechanical strength, corrosion resistance and radiation tolerance. This is because the boundaries act as traps for defects, sites for corrosion reactions and channels for diffusing other chemicals through the material.
Radiation-induced segregation
Radiation-induced segregation is a well-known phenomenon in metal alloys. When such alloys are irradiated, the bombardment of neutrons, ions and other particles creates defects. More specifically, defects known as Frenkel pairs form when an atom leaves its place in the crystal lattice (creating a vacancy) and lodges in a nearby location (becoming an interstitial). Frenkel pairs can then either recombine with each other or migrate to defect traps such as grain boundaries. If different types of atoms in the alloy move at different rates, certain elements build up or become depleted in the vicinity of the boundaries.
Because ceramics have stronger interatomic bonds than metals, researchers had long assumed that the atoms in ceramics were not subject to this type of segregation. Now, however, a team of researchers led by Izabela Szlufarska has turned this idea on its head by studying the behaviour of grain boundaries in silicon carbide (SiC). This ceramic is employed in nuclear energy and jet engines, among other high-tech applications, and it also shows promise for advanced nuclear reactors and microelectrochemical systems operating in harsh conditions.
Szlufarska and colleagues found that the material’s grain boundaries became enriched with carbon atoms when they bombarded it with ions at a temperature of 300°C. At this temperature, which is much lower than is required to initiate radiation-induced segregation in metals, they found that the radiation dislodged some carbon atoms from their normal lattice sites. Just as in metals, the resulting pair of defects in the SiC included a vacancy site and an interstitial (in this case, a loosely-bound carbon atom). They also observed that these untethered interstitials migrated towards the grain boundaries, where they accumulated, changing the material’s chemistry. The degree of segregation diminished when they irradiated the material at 600°C.
Radiation as a tool to fine-tune chemistry
The researchers obtained their result by analysing the chemical composition of grain boundaries in pristine samples of SiC grown by chemical vapour deposition using the latest scanning transmission electron microscopy techniques at UW Madison and Oak Ridge National Laboratory. They say that the phenomenon is likely to occur in other polycrystalline ceramics, too, and they also note that the segregation might be turned into an advantage, by making it possible to produce new types of ceramic materials with improved properties. “The radiation might in fact be used as a tool to fine-tune grain boundary chemistry,” explains study co-author Xing Wang.
However, the researchers, who report their findings in Nature Materials, also note that the much lower temperatures for carbon enrichment in SiC suggest that our understanding of radiation-induced segregation in metals may not transfer directly to ceramics.
“Unlike metal alloys, ceramics have much more complex energy landscapes for defect reactions and multiple sublattices in which defects can migrate,” they say. To explore this landscape, the team developed an ab initio informed rate theory model that reproduces and explains the low-temperature radiation-induced segregation behaviour in SiC. These calculations also suggest that carbon segregation near grain boundaries in SiC comes about due to two factors: the different diffusivities of vacancies and interstitial defects; and the different reaction energy barriers between silicon and carbon sublattices in the material.
In their future studies, Szlufarska and colleagues plan to study how radiation-induced segregation in SiC depends on other conditions – for example, the total dose of radiation. They will also investigate different types of grain boundaries.


physicsworld--2020-06-30--Contraceptive hydrogel proves safe in rats - Physics World

Researchers from India have developed a biodegradable gel for female contraception .
Reporting their results in Materials Science & Engineering C , they found that the active ingredient styrene maleic anhydride ( SMA ) embedded in a biodegradable hydrogel kills sperm and prevents egg cell formation .
Implanting the gel in female rats showed excellent bio-compatibility , paving the way for creation of a non-hormonal contraceptive implant .
Such a gel would expand the hormonal and non-hormonal contraceptive options currently available for women , many of which cause side effects .
SMA is already in Phase III clinical trials as @ @ @ @ @ @ @ deferens , the vessel transporting sperm in men .
But in addition to killing sperm , SMA also disrupts the development of female egg cells .
The astonishing combination of these two effects led the research team headed by Piyali Basak and Sujoy Guha to design a female version of the gel .
To achieve long-term dosing , their team wanted to incorporate SMA into a gel that would be inserted in the uterus , the female reproductive organ that nurtures the developing foetus till birth .
A suitable gel has to be @ @ @ @ @ @ @ allow the incorporation of SMA without inactivating the drug .
To create such a gel , polycaprolactone ( PCL ) proved to be a good starting point .
It is commonly used for medical applications as a biodegradable polymer ; however , it is not flexible enough for this application .
To achieve the required flexibility , the researchers mixed PCL with PEG ( polyethylene glycol ) and polymerized them as diacrylates ( DA ) .
The polymers were fabricated into a PCL-DA : PEG-DA hydrogel , a water-based gel made from an @ @ @ @ @ @ @ different concentrations of SMA and characterized the resulting gels .
First author Bhuvaneshwaran Subramanian and his team tested the physical properties and biodegradability of the gels , as well as the influence of exposure to ethanol , varying temperature and mechanical stress .
Out of the five samples with different SMA concentrations , the team further evaluated the three most promising ones using sperm and rat uterine cells .
As intended , the gel killed sperm but did not harm the uterine cells .
The sample with the highest spermicidal activity was then @ @ @ @ @ @ @ Because rats do not have a true uterus , the researchers implanted the hydrogel in the fallopian tubes , which serve as a model for the human uterus .
The implanted gel had no effect on any of the tested tissues or organs and degraded after 150 days .
Blood analysis revealed no signs of inflammation , toxicological symptoms or metabolic and hormonal changes .
These findings suggest that the SMA hydrogel should be safe for implantation in the female reproductive organs .
The next step will be to investigate whether the combination @ @ @ @ @ @ @ hydrogel also works as an effective contraceptive when implanted in rats .

The PCL-DA:PEG-DA hydrogel containing SMA is designed as a contraceptive for application in the human female uterus. It has been shown to be safe in rats and to kill sperm. (Courtesy: B Subramanian)
Researchers from India have developed a biodegradable gel for female contraception. Reporting their results in Materials Science & Engineering C, they found that the active ingredient styrene maleic anhydride (SMA) embedded in a biodegradable hydrogel kills sperm and prevents egg cell formation. Implanting the gel in female rats showed excellent bio-compatibility, paving the way for creation of a non-hormonal contraceptive implant. Such a gel would expand the hormonal and non-hormonal contraceptive options currently available for women, many of which cause side effects.
Potential for a non-hormonal female contraceptive
SMA is already in Phase III clinical trials as a male contraceptive implant in the vas deferens, the vessel transporting sperm in men. But in addition to killing sperm, SMA also disrupts the development of female egg cells. The astonishing combination of these two effects led the research team headed by Piyali Basak and Sujoy Guha to design a female version of the gel.
To achieve long-term dosing, their team wanted to incorporate SMA into a gel that would be inserted in the uterus, the female reproductive organ that nurtures the developing foetus till birth. A suitable gel has to be safe for the body, biodegradable and allow the incorporation of SMA without inactivating the drug.
To create such a gel, polycaprolactone (PCL) proved to be a good starting point. It is commonly used for medical applications as a biodegradable polymer; however, it is not flexible enough for this application. To achieve the required flexibility, the researchers mixed PCL with PEG (polyethylene glycol) and polymerized them as diacrylates (DA). The polymers were fabricated into a PCL-DA:PEG-DA hydrogel, a water-based gel made from an insoluble polymer. They then added five different concentrations of SMA and characterized the resulting gels.
Selecting the best concentration
First author Bhuvaneshwaran Subramanian and his team tested the physical properties and biodegradability of the gels, as well as the influence of exposure to ethanol, varying temperature and mechanical stress.
Sujoy Guha, Piyali Basak and Bhuvaneshwaran Subramanian. (Courtesy: B Subramanian)
Out of the five samples with different SMA concentrations, the team further evaluated the three most promising ones using sperm and rat uterine cells. As intended, the gel killed sperm but did not harm the uterine cells. The sample with the highest spermicidal activity was then chosen for implantation in a rat.
Because rats do not have a true uterus, the researchers implanted the hydrogel in the fallopian tubes, which serve as a model for the human uterus. The implanted gel had no effect on any of the tested tissues or organs and degraded after 150 days. Blood analysis revealed no signs of inflammation, toxicological symptoms or metabolic and hormonal changes.
These findings suggest that the SMA hydrogel should be safe for implantation in the female reproductive organs. The next step will be to investigate whether the combination of SMA and the PCL-DA:PEG-DA hydrogel also works as an effective contraceptive when implanted in rats.


physicsworld--2020-06-30--Colour-changing probe maps stresses in soft materials - Physics World

Directly measuring stresses in soft materials as they deform is no easy task , but a team of researchers in France and the US have now developed a colour-changing force-responsive probe that can do just that .
The device , which is based on a force-sensitive molecule embedded in an elastic polymer ( elastomer ) network , can be used to build up a quantitative map of internal forces in a structure by optical means alone .
When a mechanical load is applied to an irregularly shaped object , the stresses and strains it produces will also be irregular .
@ @ @ @ @ @ @ predicting where the object will break , but because soft materials often deform considerably before they fail , such measurements are particularly difficult to make .
At present , only a few techniques can directly measure stresses in soft materials .
The most common method is to measure strains and then perform a mathematical simulation to calculate the corresponding stresses .
Such calculations are , however , known to be unreliable for large strains and strong strain gradients .
In recent years , researchers have been exploring ways of making stress sensors out @ @ @ @ @ @ @ When these “ mechanophore ” molecules are activated by a force of a sufficient size , they undergo chemical reactions that cause their optical properties ( such as fluorescence , luminescence and colour ) to change .
One commonly used mechanophore is an organic compound known as a spiropyran .
When a spiropyran-containing polymer network deforms , the forces on the bonds of this molecule cause it to transform into a chemical variant called merocyanine that absorbs visible light .
By shining a light on the sample and monitoring its change in colour @ @ @ @ @ @ @ therefore directly measure the fraction of molecules that have undergone the chemical reaction .
This , in turn , gives them a measure of the average stress applied on the material at the point at which the colour change is observed .
“ This field of study is called mechanochemistry – that is , chemistry triggered by mechanics , ” explains Costantino Creton from the ESPCI in Paris , who led the new research effort .
“ It opens many possibilities for measuring internal forces using optical visualization techniques alone.
” Going from @ @ @ @ @ @ @ heterogenous stress fields is not as easy as it sounds , however .
For one , Creton and colleagues note that the spiropyran must be randomly and homogenously incorporated into the material being tested .
The average force produced on the molecule must also be directly related to macroscopic stress applied , and the molecular sensor should activate before the material breaks .
The researchers tested their technique on two elastomer materials with very different hardening properties .
They began by incorporating spiropyran into these materials as a cross-linker and tracked the colour @ @ @ @ @ @ @ tension to the samples along a single axis .
By varying the concentration of the spiropyran within the network of the elastomers , they produced a calibration curve of applied stress versus colour change .
They then used this stress-colour curve to determine the stress distribution around pre-existing cracks within the samples .
This stress distribution would be much more difficult to obtain using conventional techniques , as mentioned , since the materials host strong localized stress gradients .
Afterwards , the team , which also includes researchers from the University of Colorado @ @ @ @ @ @ @ fields with theoretical simulations of the same materials .
The optical measurement exactly matched these calculations , thus validating the method , Creton says .
This internal probe technique , which is detailed in Science Advances , could be used to test statistical fracture modelling of soft , tough materials and more generally to quantify stresses in irregularly shaped objects from simple optical observations with a ( red-green-blue ) camera , he adds .
The researchers say they would now like to try out their approach on composite materials with a wider range @ @ @ @ @ @ @ like to test metamaterials , which have very heterogenous internal structures and complex mechanical behaviours , ” Creton tells Physics World .
These materials are artificially engineered compounds with properties such as a negative Poisson ratio that are rare or absent in natural materials .

The observed change in colour of elongated samples. (Courtesy: C Creton)
Directly measuring stresses in soft materials as they deform is no easy task, but a team of researchers in France and the US have now developed a colour-changing force-responsive probe that can do just that. The device, which is based on a force-sensitive molecule embedded in an elastic polymer (elastomer) network, can be used to build up a quantitative map of internal forces in a structure by optical means alone.
When a mechanical load is applied to an irregularly shaped object, the stresses and strains it produces will also be irregular. Measuring these internal forces is important for predicting where the object will break, but because soft materials often deform considerably before they fail, such measurements are particularly difficult to make.
At present, only a few techniques can directly measure stresses in soft materials. The most common method is to measure strains and then perform a mathematical simulation to calculate the corresponding stresses. Such calculations are, however, known to be unreliable for large strains and strong strain gradients.
Force-sensitive molecules
In recent years, researchers have been exploring ways of making stress sensors out of force-sensitive molecules incorporated into polymers. When these “mechanophore” molecules are activated by a force of a sufficient size, they undergo chemical reactions that cause their optical properties (such as fluorescence, luminescence and colour) to change.
One commonly used mechanophore is an organic compound known as a spiropyran. When a spiropyran-containing polymer network deforms, the forces on the bonds of this molecule cause it to transform into a chemical variant called merocyanine that absorbs visible light. By shining a light on the sample and monitoring its change in colour from transparent to blue, researchers can therefore directly measure the fraction of molecules that have undergone the chemical reaction. This, in turn, gives them a measure of the average stress applied on the material at the point at which the colour change is observed.
Mechanochemistry
“This field of study is called mechanochemistry – that is, chemistry triggered by mechanics,” explains Costantino Creton from the ESPCI in Paris, who led the new research effort. “It opens many possibilities for measuring internal forces using optical visualization techniques alone.”
Going from qualitative colour-change detection to quantitative mapping of heterogenous stress fields is not as easy as it sounds, however. For one, Creton and colleagues note that the spiropyran must be randomly and homogenously incorporated into the material being tested. The average force produced on the molecule must also be directly related to macroscopic stress applied, and the molecular sensor should activate before the material breaks.
A calibration curve
The researchers tested their technique on two elastomer materials with very different hardening properties. They began by incorporating spiropyran into these materials as a cross-linker and tracked the colour change of the molecule as they applied tension to the samples along a single axis. By varying the concentration of the spiropyran within the network of the elastomers, they produced a calibration curve of applied stress versus colour change. They then used this stress-colour curve to determine the stress distribution around pre-existing cracks within the samples. This stress distribution would be much more difficult to obtain using conventional techniques, as mentioned, since the materials host strong localized stress gradients.
Afterwards, the team, which also includes researchers from the University of Colorado at Boulder, compared the experimental stress fields with theoretical simulations of the same materials. The optical measurement exactly matched these calculations, thus validating the method, Creton says.
This internal probe technique, which is detailed in Science Advances, could be used to test statistical fracture modelling of soft, tough materials and more generally to quantify stresses in irregularly shaped objects from simple optical observations with a (red-green-blue) camera, he adds.
The researchers say they would now like to try out their approach on composite materials with a wider range of applications. “We would also like to test metamaterials, which have very heterogenous internal structures and complex mechanical behaviours,” Creton tells Physics World. These materials are artificially engineered compounds with properties such as a negative Poisson ratio that are rare or absent in natural materials.


physicsworld--2020-06-29--Quantum dot solar cells get greener - Physics World

Semiconducting nanocrystals called colloidal quantum dots ( CQDs ) are ideal for applications such as large-panel displays and photovoltaic cells thanks to their high efficiency and colour purity .
Their main drawback is their toxicity , since they have traditionally been made from cadmium or other heavy metals , such as lead .
Researchers at the Los Alamos National Laboratory in the US have now engineered cadmium-free QD solar cells that reach efficiencies on par with those of their environmentally-unfriendly counterparts .
The key to the new devices ’ high performance is their tolerance to defects , they say .
@ @ @ @ @ @ @ which means that films of these nanocrystals can be deposited quickly and easily on a range of flexible or rigid substrates – just like paint or ink .
Such semiconducting nanocrystals are ideal for making highly-efficient inorganic solar cells that emit light via a process known as radiative recombination .
Here , an electron in the valency energy band in the QD absorbs a photon and moves to the conduction band , leaving behind an electron vacancy , or hole .
The excited electron and hole then recombine , releasing a photon .
@ @ @ @ @ @ @ materials in solar cells is that they absorb light over a broad spectrum of solar radiation wavelengths .
This is because the band gap of a CQD can be tuned over a large energy range by simply changing the size of the nanocrystals .
Such a size-tuneable property has allowed the efficiencies of these QDs to rapidly approach those of traditional thin-film photovoltaics , such as PbS , CdTe and Pb-halide perovskite QDs .
A team of researchers led by Victor Klimov have now developed high-efficiency QD solar cells that are free from @ @ @ @ @ @ @ new devices by reacting copper , indium and selenium and then adding zinc to the mix to produce zinc-doped QDs .
They then incorporated these QDs into voids of a highly porous titanium dioxide ( TiO ) film , which plays the part of a charge-collecting electrode .
The electrode was immersed in a Na S electrolyte .
When the QDs in the device absorb incoming photons from sunlight , tightly bound electrons in the valence band get excited into a high-mobility conduction band .
These electrons subsequently migrate to the TiO electrode @ @ @ @ @ @ @ .
The researchers say they were “ pleasantly surprised ” by the results of photovoltaic and spectroscopic measurements on the new devices .
Because their QDs have a very complex composition – four elements are combined in the same nanosized particle – they are prone to ( intragap ) defects , Klimov explains .
These defects act as traps in which electrons get stuck , which means that electrons and holes have time to recombine instead of being whisked apart to produce useful current .
“ However , despite these imperfections , the @ @ @ @ @ @ @ the new solar cells , ” says Klimov .
“ Per each 100 absorbed photons , we detected 85 photogenerated electrons , implying that the photon-to-electron conversion efficiency was 85 % .
” According to the Los Alamos team , who report their work in Nature Energy , the defects in their material actually help the photoconversion process along , rather than impeding it .
In particular , the material ’ s high photovoltaic efficiency stems from a peculiar mechanism involving two types of intragap defects , they explain .
The first , @ @ @ @ @ @ @ enhance electron transfer between the QDs and TiO electrode .
The second , identified as Cu1+ hole-trapping defects , help transfer holes between the QDs and the electrolyte .
The traditional assumption that surface defects are always detrimental thus does not seem to hold true for ZCISe QDs , they say .
Indeed , the structures may even be protecting electrons and holes from unwanted recombination .
This implies that surface traps are electronically coupled to the TiO electrode and , importantly , that the energy of these traps is high enough for @ @ @ @ @ @ @ conduction band .
The high photoconversion efficiencies , combined with the remarkable defect tolerance and toxic-element-free composition of these QDs makes them promising materials for a commercially viable solar-cell technology , they conclude .

SEM image of electrodes infiltrated with quantum dots. Courtesy: LANL
Semiconducting nanocrystals called colloidal quantum dots (CQDs) are ideal for applications such as large-panel displays and photovoltaic cells thanks to their high efficiency and colour purity. Their main drawback is their toxicity, since they have traditionally been made from cadmium or other heavy metals, such as lead. Researchers at the Los Alamos National Laboratory in the US have now engineered cadmium-free QD solar cells that reach efficiencies on par with those of their environmentally-unfriendly counterparts. The key to the new devices’ high performance is their tolerance to defects, they say.
CQDs can be synthesized in solution, which means that films of these nanocrystals can be deposited quickly and easily on a range of flexible or rigid substrates – just like paint or ink. Such semiconducting nanocrystals are ideal for making highly-efficient inorganic solar cells that emit light via a process known as radiative recombination. Here, an electron in the valency energy band in the QD absorbs a photon and moves to the conduction band, leaving behind an electron vacancy, or hole. The excited electron and hole then recombine, releasing a photon.
The advantage of using CQDs as photovoltaic materials in solar cells is that they absorb light over a broad spectrum of solar radiation wavelengths. This is because the band gap of a CQD can be tuned over a large energy range by simply changing the size of the nanocrystals. Such a size-tuneable property has allowed the efficiencies of these QDs to rapidly approach those of traditional thin-film photovoltaics, such as PbS, CdTe and Pb-halide perovskite QDs.
Free from toxic elements
A team of researchers led by Victor Klimov have now developed high-efficiency QD solar cells that are free from any toxic elements. They made their new devices by reacting copper, indium and selenium and then adding zinc to the mix to produce zinc-doped QDs. They then incorporated these QDs into voids of a highly porous titanium dioxide (TiO 2 ) film, which plays the part of a charge-collecting electrode. The electrode was immersed in a Na 2 S electrolyte.
When the QDs in the device absorb incoming photons from sunlight, tightly bound electrons in the valence band get excited into a high-mobility conduction band. These electrons subsequently migrate to the TiO 2 electrode, generating a current in the process.
The researchers say they were “pleasantly surprised” by the results of photovoltaic and spectroscopic measurements on the new devices. Because their QDs have a very complex composition – four elements are combined in the same nanosized particle – they are prone to (intragap) defects, Klimov explains. These defects act as traps in which electrons get stuck, which means that electrons and holes have time to recombine instead of being whisked apart to produce useful current.
“However, despite these imperfections, the ZCISe QDs showed near perfect performance in the new solar cells,” says Klimov. “Per each 100 absorbed photons, we detected 85 photogenerated electrons, implying that the photon-to-electron conversion efficiency was 85%.”
Defect-mediated photoconversion
According to the Los Alamos team, who report their work in Nature Energy, the defects in their material actually help the photoconversion process along, rather than impeding it. In particular, the material’s high photovoltaic efficiency stems from a peculiar mechanism involving two types of intragap defects, they explain. The first, identified as shallow surface-located electron traps, enhance electron transfer between the QDs and TiO 2 electrode. The second, identified as Cu1+ hole-trapping defects, help transfer holes between the QDs and the electrolyte.
The traditional assumption that surface defects are always detrimental thus does not seem to hold true for ZCISe QDs, they say. Indeed, the structures may even be protecting electrons and holes from unwanted recombination. This implies that surface traps are electronically coupled to the TiO 2 electrode and, importantly, that the energy of these traps is high enough for electrons to transfer efficiently into the TiO 2 conduction band.
The high photoconversion efficiencies, combined with the remarkable defect tolerance and toxic-element-free composition of these QDs makes them promising materials for a commercially viable solar-cell technology, they conclude.


physicsworld--2020-06-29--Electron accelerator recycles energy - Physics World

Physicists usually have no shortage of plans to build very expensive particle accelerators – but some researchers are working to make accelerator technology cheaper , and one way is to recycle much of the energy initially used to accelerate particles .
A collaboration in the US has now shown it can successfully operate such an “ energy recovery linac ” by combining superconducting cavities with precisely designed permanent magnets .
The synchrotron has long been a popular way of accelerating electrons and other charged particles .
Energy is transferred to bunches of charged particles by sending them through a series @ @ @ @ @ @ @ on a circular path for thousands of orbits .
These machines are widely used both as high-energy colliders and as sources of very bright X-rays for a wide range of science .
While this cyclic acceleration produces very high average powers , the bunches of particles will gradually spread out and lose intensity as well as polarization .
As a result , linear accelerators ( linacs ) are used to create the brightest particle beams .
These fire particles in a single shot along a straight section of cavities , yielding bunches with @ @ @ @ @ @ @ But these machines also have a downside – they consume a huge amount of energy per shot , which limits their firing rate .
Best of both worlds Energy recovery linacs ( ERLs ) are designed to combine the best of both worlds .
These devices send electrons through a linac and then guide them around a circuit back to the accelerator entrance – with just a few having had their energy tapped along the way .
This process takes place N times , with the particles gaining energy on each turn .
@ @ @ @ @ @ @ to a shift in the electrons ’ path length of half a cavity wavelength .
The particles travel another N times around the circuit , but rather than absorbing additional energy from the cavities they instead give it back .
Once their turns are complete and they have shed all the energy they originally acquired , they are dumped .
With most of this energy transferred to other electrons subsequently injected into the circuit , which themselves go through the same 2N cycles , an ERL can accelerate a given number of particles @ @ @ @ @ @ @ consumed by the equivalent linac .
In principle , this allows such a device either to generate much higher luminosities from a given electricity budget , or to consume less power for a given luminosity .
While the latter option would reduce operating costs , both should lower construction costs – given that linac cavities are more expensive to build than the magnets used to steer electrons .
The idea is not new , having been put forward originally by Maury Tigner at Cornell University in the US in 1965 .
However , @ @ @ @ @ @ @ of hurdles in the intervening decades .
One has been developing the superconducting cavities that make linacs more energy-efficient .
Another challenge has been merging beams at the linac entrance and separating them at its exit , as well as dealing with the higher-order modes inside cavities that can cause particle bunches to break up .
Difficulties notwithstanding , the scheme has been put into practice at several locations including Novosibirsk State University in Russia , which operated a copper-cavity ERL with multiple turns ( N=4 ) for the first time .
The @ @ @ @ @ @ @ Hoffstaetter of Cornell University and colleagues , makes progress by instead demonstrating multiple passes using a superconducting linac .
The Cornell Brookhaven Energy-Recovery-Linac Test Accelerator ( CBETA ) has been built and tested at Cornell but relies on magnets developed by Dejan Trbojevic and team at Brookhaven National Laboratory .
These are quite different to the electromagnets used in synchrotrons , whose fields ramp up to prevent electrons from flying out of the machine as they pick up speed — but can not accommodate electrons with different energies .
Instead , the CBETA @ @ @ @ @ @ @ it can simultaneously guide eight sets of electrons , with four different energies , around the circuit back to the linac .
Being permanent , rather than electromagnetic , these “ fixed-field alternating-gradient ” magnets provide an additional energy-saving feature over traditional linacs .
Hoffstaetter and colleagues carried out the first test of CBETA in June last year , showing that the machine could recuperate 99.8 % of its input energy after accelerating and decelerating electrons in single passes .
Then just before Christmas , the researchers demonstrated the full complement of eight @ @ @ @ @ @ @ paper accepted for publication in Physical Review Letters , they took electrons 6 MeV kinetic energy and stepped their energy up to 42 , 78 , 114 and 150 MeV , before stepping the energy down so that it ended up back at 6 MeV .
The researchers say that the CBETA technology could be used in a variety of applications including medical isotope production , cancer therapy or in the manufacture of microchips .
It has also been designed to show how to “ cool ” ions that will be collided in @ @ @ @ @ @ @ construction at the Brookhaven lab in January .
Designed to probe the composition of protons and neutrons with unprecedented precision , the collider relies on minimizing particles ’ energy to maximize collision rates .
Having shown that CBETA can work in principle , Hoffstaetter and colleagues are now working to boost its performance .
To protect equipment and personnel , they restricted the machine ’ s current on the December run to just a few nanoamps .
But they now want to raise that towards a target of 40 mA .
“ A @ @ @ @ @ @ @ next stage of this accelerator , ” they write .

Energy recyclers: Cornell’s Georg Hoffstaetter (left) and Brookhaven’s Dejan Trbojevic. (Courtesy: Cornell University)
Physicists usually have no shortage of plans to build very expensive particle accelerators – but some researchers are working to make accelerator technology cheaper, and one way is to recycle much of the energy initially used to accelerate particles. A collaboration in the US has now shown it can successfully operate such an “energy recovery linac” by combining superconducting cavities with precisely designed permanent magnets.
The synchrotron has long been a popular way of accelerating electrons and other charged particles. Energy is transferred to bunches of charged particles by sending them through a series of radiofrequency cavities while magnets keep them on a circular path for thousands of orbits. These machines are widely used both as high-energy colliders and as sources of very bright X-rays for a wide range of science.
While this cyclic acceleration produces very high average powers, the bunches of particles will gradually spread out and lose intensity as well as polarization. As a result, linear accelerators (linacs) are used to create the brightest particle beams. These fire particles in a single shot along a straight section of cavities, yielding bunches with very high energies and exceptional intensities. But these machines also have a downside – they consume a huge amount of energy per shot, which limits their firing rate.
Best of both worlds
Energy recovery linacs (ERLs) are designed to combine the best of both worlds. These devices send electrons through a linac and then guide them around a circuit back to the accelerator entrance – with just a few having had their energy tapped along the way. This process takes place N times, with the particles gaining energy on each turn. Then the logic is reversed, thanks to a shift in the electrons’ path length of half a cavity wavelength. The particles travel another N times around the circuit, but rather than absorbing additional energy from the cavities they instead give it back. Once their turns are complete and they have shed all the energy they originally acquired, they are dumped.
With most of this energy transferred to other electrons subsequently injected into the circuit, which themselves go through the same 2N cycles, an ERL can accelerate a given number of particles using a small fraction of the energy consumed by the equivalent linac. In principle, this allows such a device either to generate much higher luminosities from a given electricity budget, or to consume less power for a given luminosity. While the latter option would reduce operating costs, both should lower construction costs – given that linac cavities are more expensive to build than the magnets used to steer electrons.
The idea is not new, having been put forward originally by Maury Tigner at Cornell University in the US in 1965. However, the scheme had to overcome a number of hurdles in the intervening decades. One has been developing the superconducting cavities that make linacs more energy-efficient. Another challenge has been merging beams at the linac entrance and separating them at its exit, as well as dealing with the higher-order modes inside cavities that can cause particle bunches to break up. Difficulties notwithstanding, the scheme has been put into practice at several locations including Novosibirsk State University in Russia, which operated a copper-cavity ERL with multiple turns (N=4) for the first time.
Multiple passes
The latest work, carried out by Georg Hoffstaetter of Cornell University and colleagues, makes progress by instead demonstrating multiple passes using a superconducting linac. The Cornell Brookhaven Energy-Recovery-Linac Test Accelerator (CBETA) has been built and tested at Cornell but relies on magnets developed by Dejan Trbojevic and team at Brookhaven National Laboratory. These are quite different to the electromagnets used in synchrotrons, whose fields ramp up to prevent electrons from flying out of the machine as they pick up speed — but cannot accommodate electrons with different energies. Instead, the CBETA magnets generate a field shaped so that it can simultaneously guide eight sets of electrons, with four different energies, around the circuit back to the linac. Being permanent, rather than electromagnetic, these “fixed-field alternating-gradient” magnets provide an additional energy-saving feature over traditional linacs.
Hoffstaetter and colleagues carried out the first test of CBETA in June last year, showing that the machine could recuperate 99.8% of its input energy after accelerating and decelerating electrons in single passes. Then just before Christmas, the researchers demonstrated the full complement of eight passes. As they report in a paper accepted for publication in Physical Review Letters, they took electrons 6 MeV kinetic energy and stepped their energy up to 42, 78, 114 and 150 MeV, before stepping the energy down so that it ended up back at 6 MeV.
The researchers say that the CBETA technology could be used in a variety of applications including medical isotope production, cancer therapy or in the manufacture of microchips. It has also been designed to show how to “cool” ions that will be collided in the $2bn Electron-Ion Collider approved for construction at the Brookhaven lab in January. Designed to probe the composition of protons and neutrons with unprecedented precision, the collider relies on minimizing particles’ energy to maximize collision rates.
Having shown that CBETA can work in principle, Hoffstaetter and colleagues are now working to boost its performance. To protect equipment and personnel, they restricted the machine’s current on the December run to just a few nanoamps. But they now want to raise that towards a target of 40 mA. “A push to high current will be the next stage of this accelerator,” they write.


physicsworld--2020-06-27--Two new frequency combs could boost telecoms and molecular fingerprinting - Physics World

Frequency combs are one of the most important developments in metrology in the 21st century , but conventional combs are bulky and highly sensitive to external perturbations .
Now two independent groups present key developments in solid state frequency combs that could lead to robust , convenient combs for use outside the laboratory .
The first is an integrated , telecommunications-wavelength comb that stabilizes itself every time it is turned on .
The second uses a completely new mechanism to generate frequency comb emission in the mid-infrared – a region crucial for molecular spectroscopy .
Frequency combs are pulsed lasers @ @ @ @ @ @ @ they produce extremely short pulses that comprise light at regularly spaced frequencies .
By fixing one of these frequencies very precisely – for example using an atomic clock – one can measure the frequency of a light signal by studying how far along the comb it falls from this reference frequency .
Frequency combs have proved immensely useful in the laboratory for building better atomic clocks , improving time and frequency standards and also doing ultracold atomic and molecular spectroscopy .
The use of traditional frequency combs , however , is constrained by @ @ @ @ @ @ @ , amplifiers and other components such as isolators to prevent feedback from destabilizing the laser .
In the past decade or so , researchers have sought more user-friendly devices for applications such as fibre-optic multiplexing , time-keeping and molecular detection .
In 2018 , researchers at Columbia University in New York City led by Michal Lipson and Alexander Gaeta unveiled a solid-state , telecoms-compatible frequency comb that eliminated many specialist components .
It used a low-power , electrically-pumped semiconductor laser .
When a solid-state microresonator was injected with light at 1579 nm wavelength @ @ @ @ @ @ @ at precisely spaced frequencies .
The proportion of the energy in these modes gradually increased , forming a frequency comb .
Although this was a huge breakthrough , there were difficulties .
A complex process was required to achieve and maintain the comb operation , and even then it did not reliably produce phase- and intensity-stable pulses called solitons .
“ If it ’ s not producing solitons , it ’ s not a quiet comb ” , explains John Bowers of the University of California , Santa Barbara , “ If you @ @ @ @ @ @ @ or a lidar , or a wavelength division multiplexing transmission system , you don ’ t want modulation instability .
It ’ s not useful for most applications.
” Now , Santa Barbara researchers led by Bowers , together with scientists at Caltech and EPFL in Switzerland , unveil an integrated , solid-state laser that solves these problems .
Whereas traditional frequency combs need to prevent feedback between a microresonator and the laser , this latest design utilized feedback .
A cheap semiconductor laser called a distributed feedback ( DFB ) laser was @ @ @ @ @ @ @ a small , precisely-controlled distance from a microresonator mounted on another chip .
A physically complex non-linear interaction between the laser cavity and the microresonator created a very simple result : every time the laser was switched on , the microresonator automatically tuned itself to produce solitons .
Remarkably , the resulting frequency comb had orders of magnitude lower noise than the original laser : “ DFB lasers are crappy , ” says Bowers , “ People pay $ 60,000 for a laser to get linewidths that aren ’ t as good as @ @ @ @ @ @ @ tolerated environmental disturbances such as temperature fluctuations .
The researchers hope their device could make frequency combs much more widespread : “ We believe we can very soon integrate this all onto a single chip , ” says Bowers .
“ It could be a millimetre long , it could be mass produced , it could be quite cheap , and it wouldn ’ t take a PhD to run .
That ’ s what ’ s exciting about this.
” Gaeta is impressed : “ You can argue that microresonator combs have @ @ @ @ @ @ @ photonics in the past decade , ” he says .
“ My work with Michal Lipson was the first real integrated system and these guys have made an another important step in further integrating it and making the system ‘ turnkey ’ .
It ’ s an important advance in taking this technology into the field.
” Meanwhile at Harvard University , Federico Capasso and colleagues focussed on creating frequency combs that operate in the mid-infrared region at 2.5-10 µm wavelength – a part of the electromagnetic spectrum in which molecules have unique @ @ @ @ @ @ @ ( QCLs ) are readily available in this region , turning them into frequency combs has proven very difficult .
Capasso ’ s team investigated the possibility of producing a mid-infrared frequency comb from a quantum cascade ring laser , which behaves as its own microresonator when electrically injected .
Traditional QCL frequency combs rely on bar-shaped cavities to create standing waves – something that does not happen in a symmetric ring cavity .
So , the researchers added a defect to the ring to break this symmetry and allow standing waves to @ @ @ @ @ @ @ we put a few perfect rings on the chip , ” explains Harvard ’ s Marco Piccardo .
“ To our surprise , these were also forming frequency combs…This is where we started scratching our heads.
” After much theoretical analysis of the laser physics , the researchers realized that the explanation lay in an instability in a non-linear differential equation called the complex Ginzburg-Landau equation , which describes spatially extended systems of coupled non-linear oscillators : “ It ’ s not observed in bars , ” says Piccardo , “ The fact @ @ @ @ @ @ @ this frequency comb regime is a new type of turbulent instability for quantum cascade lasers – although it ’ s been observed before in very different physical systems like superconductors and Bose-Einstein condensates.
” The process happens in two stages : first , the single laser mode breaks up into a turbulent , unstable waveform .
Eventually energy becomes concentrated in the harmonics of the original laser frequency , forming a frequency comb – albeit one with only around nine teeth .
“ There is much , much more to do , ” @ @ @ @ @ @ @ physics was so far shown to be restricted to the world of Kerr combs .
I think all this can now be shown to be possible in QCLs and on this we just made a first step .
I don ’ t think the two systems are competitors because they are going to impact on different spectral ranges , but I think we can learn from each other.
” Both Capasso ’ s and Bowers ’ teams have described their results in Nature .
“ Both these papers have in common the problem @ @ @ @ @ @ @ be hooked up to a battery to produce a broadband comb source , ” says Scott Diddams , who is at the National Institute of Standards and Technology in Boulder , Colorado and was not involved with either group .
“ The Bowers paper is much more about the nitty gritty of solving a hard problem that is going to make frequency combs prolific .
The Capasso paper is an interesting , non-linear optical and general non-linear science result , but it will require additional engineering to increase the bandwidth to make it @ @ @ @ @ @ @ ”

Ringing in the new: microscope image of a ring laser used by the Harvard group. (Courtesy: Capasso Lab/Harvard SEAS)
Frequency combs are one of the most important developments in metrology in the 21st century, but conventional combs are bulky and highly sensitive to external perturbations. Now two independent groups present key developments in solid state frequency combs that could lead to robust, convenient combs for use outside the laboratory. The first is an integrated, telecommunications-wavelength comb that stabilizes itself every time it is turned on. The second uses a completely new mechanism to generate frequency comb emission in the mid-infrared – a region crucial for molecular spectroscopy.
Frequency combs are pulsed lasers often described as rulers of light because they produce extremely short pulses that comprise light at regularly spaced frequencies. By fixing one of these frequencies very precisely – for example using an atomic clock – one can measure the frequency of a light signal by studying how far along the comb it falls from this reference frequency. Frequency combs have proved immensely useful in the laboratory for building better atomic clocks, improving time and frequency standards and also doing ultracold atomic and molecular spectroscopy.
The use of traditional frequency combs, however, is constrained by their need for high-power, ultrastable lasers, amplifiers and other components such as isolators to prevent feedback from destabilizing the laser. In the past decade or so, researchers have sought more user-friendly devices for applications such as fibre-optic multiplexing, time-keeping and molecular detection.
Simple components
In 2018, researchers at Columbia University in New York City led by Michal Lipson and Alexander Gaeta unveiled a solid-state, telecoms-compatible frequency comb that eliminated many specialist components. It used a low-power, electrically-pumped semiconductor laser. When a solid-state microresonator was injected with light at 1579 nm wavelength, Kerr non-linearity caused sidebands to appear at precisely spaced frequencies. The proportion of the energy in these modes gradually increased, forming a frequency comb.
Although this was a huge breakthrough, there were difficulties. A complex process was required to achieve and maintain the comb operation, and even then it did not reliably produce phase- and intensity-stable pulses called solitons. “If it’s not producing solitons, it’s not a quiet comb”, explains John Bowers of the University of California, Santa Barbara, “If you want to make an atomic clock, or a lidar, or a wavelength division multiplexing transmission system, you don’t want modulation instability. It’s not useful for most applications.”
Now, Santa Barbara researchers led by Bowers, together with scientists at Caltech and EPFL in Switzerland, unveil an integrated, solid-state laser that solves these problems. Whereas traditional frequency combs need to prevent feedback between a microresonator and the laser, this latest design utilized feedback.
Much lower noise
A cheap semiconductor laser called a distributed feedback (DFB) laser was integrated into a chip that was placed a small, precisely-controlled distance from a microresonator mounted on another chip. A physically complex non-linear interaction between the laser cavity and the microresonator created a very simple result: every time the laser was switched on, the microresonator automatically tuned itself to produce solitons. Remarkably, the resulting frequency comb had orders of magnitude lower noise than the original laser: “DFB lasers are crappy,” says Bowers, “People pay $60,000 for a laser to get linewidths that aren’t as good as this.” Moreover, the soliton state tolerated environmental disturbances such as temperature fluctuations.
The researchers hope their device could make frequency combs much more widespread: “We believe we can very soon integrate this all onto a single chip,” says Bowers. “It could be a millimetre long, it could be mass produced, it could be quite cheap, and it wouldn’t take a PhD to run. That’s what’s exciting about this.”
Turnkey system
Gaeta is impressed: “You can argue that microresonator combs have been the most active field in non-linear photonics in the past decade,” he says. “My work with Michal Lipson was the first real integrated system and these guys have made an another important step in further integrating it and making the system ‘turnkey’. It’s an important advance in taking this technology into the field.”
Meanwhile at Harvard University, Federico Capasso and colleagues focussed on creating frequency combs that operate in the mid-infrared region at 2.5-10 µm wavelength – a part of the electromagnetic spectrum in which molecules have unique spectral fingerprints. While quantum cascade lasers (QCLs) are readily available in this region, turning them into frequency combs has proven very difficult.
Surprising result
Capasso’s team investigated the possibility of producing a mid-infrared frequency comb from a quantum cascade ring laser, which behaves as its own microresonator when electrically injected. Traditional QCL frequency combs rely on bar-shaped cavities to create standing waves – something that does not happen in a symmetric ring cavity. So, the researchers added a defect to the ring to break this symmetry and allow standing waves to form. “Purely as controls, we put a few perfect rings on the chip,” explains Harvard’s Marco Piccardo. “To our surprise, these were also forming frequency combs…This is where we started scratching our heads.”
After much theoretical analysis of the laser physics, the researchers realized that the explanation lay in an instability in a non-linear differential equation called the complex Ginzburg-Landau equation, which describes spatially extended systems of coupled non-linear oscillators: “It’s not observed in bars,” says Piccardo, “The fact that a ring laser can go into this frequency comb regime is a new type of turbulent instability for quantum cascade lasers – although it’s been observed before in very different physical systems like superconductors and Bose-Einstein condensates.” The process happens in two stages: first, the single laser mode breaks up into a turbulent, unstable waveform. Eventually energy becomes concentrated in the harmonics of the original laser frequency, forming a frequency comb – albeit one with only around nine teeth.
“There is much, much more to do,” says Piccardo. “Plenty of interesting physics was so far shown to be restricted to the world of Kerr combs. I think all this can now be shown to be possible in QCLs and on this we just made a first step. I don’t think the two systems are competitors because they are going to impact on different spectral ranges, but I think we can learn from each other.”
Both Capasso’s and Bowers’ teams have described their results in Nature.
“Both these papers have in common the problem of trying to make devices that can be hooked up to a battery to produce a broadband comb source,” says Scott Diddams, who is at the National Institute of Standards and Technology in Boulder, Colorado and was not involved with either group. “The Bowers paper is much more about the nitty gritty of solving a hard problem that is going to make frequency combs prolific. The Capasso paper is an interesting, non-linear optical and general non-linear science result, but it will require additional engineering to increase the bandwidth to make it more useful for frequency comb spectroscopy.”


physicsworld--2020-06-26--Exotic locales for alien life, meet a 16-year-old satellite scientist - Physics World

Breakthrough Listen is an organization that searches for evidence of technological life by surveying one million nearby stars in the Milky Way as well as 100 nearby galaxies .
The search has been going for five years and uses a wide range of radio and optical bands .
Needless to say , no definitive evidence of life has been found .
In a bid to expand the scope of the search , Breakthrough Listen has come up with a catalogue of “ Exotica ” , which includes 700 distinct objects that will targeted in the search .
The idea is @ @ @ @ @ @ @ stars that could have Earth-like planets and look at “ one of everything ” in the observable universe .
The targets range from comets to galaxies as well as some of the most rare and violent celestial phenomena .
Examples include Tabby ’ s Star , which has a bizarre dimming behaviour ; and the interstellar object ’ Oumuamua , which passed near Earth in 2017 .
Julie Sage runs experiments in space on cubesats and hosts a science news channel on YouTube – not bad for a 16-year-old .
In this Via @ @ @ @ @ @ @ challenges of being a young scientist , space exploration and communicating science to young people .
In the video below , Sage talks about Physics World ‘ s favourite crustacean : the mighty mantis shrimp .

Interstellar umbrella: artist’s impression of ‘’Oumuamua, which some astronomers claim could be an alien light-sail. (Courtesy: ESO/M Kornmesser)
Breakthrough Listen is an organization that searches for evidence of technological life by surveying one million nearby stars in the Milky Way as well as 100 nearby galaxies. The search has been going for five years and uses a wide range of radio and optical bands.
Needless to say, no definitive evidence of life has been found. In a bid to expand the scope of the search, Breakthrough Listen has come up with a catalogue of “Exotica”, which includes 700 distinct objects that will targeted in the search. The idea is to go beyond the usual targets of stars that could have Earth-like planets and look at “one of everything” in the observable universe.
The targets range from comets to galaxies as well as some of the most rare and violent celestial phenomena. Examples include Tabby’s Star, which has a bizarre dimming behaviour; and the interstellar object ’Oumuamua, which passed near Earth in 2017.
Cubestat scientist
Julie Sage runs experiments in space on cubesats and hosts a science news channel on YouTube – not bad for a 16-year-old. In this Via Satellite podcast, Sage talks about the challenges of being a young scientist, space exploration and communicating science to young people.
In the video below, Sage talks about Physics World‘s favourite crustacean: the mighty mantis shrimp.


physicsworld--2020-06-26--In-line spectral monitoring gets ready to shine - Physics World

Ocean Insight , a US manufacturer of specialist spectral systems , software and optical solutions , has high hopes for its Liquid Transmission Measurement System ( LTMS ) , a spectroscopy-based unit for real-time , in-line optical monitoring of liquid concentration levels in a range of industrial plating , colouring and coating applications .
The modular system comprises a rugged optical sensing platform – spectrometer , control unit and machine-learning software – within a compact benchtop configuration that ’ s suitable for day-to-day deployment into harsh industrial environments .
As such , the LTMS is able to generate high-precision colour @ @ @ @ @ @ @ on a 24/7 basis , with flow-cell set-up and automatic fluid handling or built-in cuvette holder .
Right now , the LTMS is being sold directly into industry end-users and , once tailored to the customer ’ s requirements , comes ready to use “ out of the box ” in the manufacturing facility .
“ Alternatively , if the end-user has a preferred OEM integrator , the LTMS can be incorporated as part of their existing ‘ smart factory system ’ , with or without fluid-handling capability , ” explains Scott Scargle @ @ @ @ @ @ @ Insight .
Getting the priorities right Despite a myriad of potential LTMS applications , Ocean Insight ’ s near-term focus for the product is in the consumer electronics and food processing industries .
Colour consistency of external parts – for Bluetooth speakers , MP3 players and the like – is a major pain-point in the consumer electronics supply chain , with batch-to-batch consistency of anodized aluminium being notoriously difficult to control .
Anodization is an electrolytic process to create a protective , anti-corrosion layer on the aluminium surface – a coating that can @ @ @ @ @ @ @ range of colours .
Trouble is , anodization chemistry remains something of a black art , with colour materials and finishing ( CMF ) designers and contract manufacturers forced to work with wide colour tolerances and complex production processes .
If that ’ s the problem , the LTMS looks a lot like the answer .
With its ability to measure solution concentrations in the anodization tank out on the factory floor , those CMF tolerances can actually get a lot tighter – which translates into enhanced repeatability , less scrap and streamlined @ @ @ @ @ @ @ , ” notes Scargle , “ the LTMS gives the CMF designers a wider colour palette to choose from , while the contract manufacturers can make their parts with better consistency.
” In the food-processing industry , meanwhile , the LTMS is being lined up to support specialist coating applications on a range of foodstuffs .
A case in point is the wax coatings that packing-houses apply to citrus fruits – typically to prolong the shelf-life and enhance the visual appeal of the fruit , also to act as a carrier for antifungal @ @ @ @ @ @ @ balancing act , ” says Scargle .
“ The LTMS can be used to make sure concentration levels are within a certain tolerance to meet health and safety requirements , while high enough to maintain a level of effectiveness.
” Another use-case is the application of pesticides to food crops .
Before a pesticide mix is applied in the field , for example , the LTMS is able to verify that the concentration falls within a window of acceptance to meet statutory safety guidelines .
“ Equally important , ” adds Scargle , @ @ @ @ @ @ @ check the rinse water after the pesticide storage tank is cleaned , ensuring there are no unwanted residuals left behind that may end up being sprayed on crops later.
” When it comes to customer upside , one of the big advantages of the LTMS is in-line deployment – a feature that makes it possible to more readily address quality issues as they occur .
Consider an aluminium anodization coating tank , the electrolytes of which need to be analysed versus pass/fail criteria on a regular basis .
Traditionally that testing has relied @ @ @ @ @ @ @ , high-performance liquid chromatography ( HPLC ) – in a central laboratory ( or more often an offsite testing facility for smaller contract manufacturers ) .
All of which is time-consuming , manually intensive and can mean significant process downtime while the results are pending .
“ The LTMS essentially eliminates that whole walk-to-lab workflow , ” says Lu Luo , sales director at Ocean Insight and head of the company ’ s development facility in Rochester , New York .
“ It ’ s about the benefits of real-time , in-line diagnostics @ @ @ @ @ @ @ greater process uptime – versus manually intensive and centralized lab testing.
” What ’ s more , the LTMS workflow is such that scientific staff are no longer tied up on routine quality-control tasks .
“ It ’ s a portable unit and can be operated from a user-friendly interface by a technician , ” Luo adds .
Another notable feature of the LTMS is the innovative use of machine-learning technology .
Each customer gets a tailored system that ’ s “ trained ” for their specific optical sensing applications versus a number @ @ @ @ @ @ @ models provide a direct answer on solution concentrations for pass–fail manufacturing decisions – either on the technician ’ s display or sent digitally to a central manufacturing execution system , ” says Luo .
It ’ s a neat innovation that comes with in-built scalability .
“ Customers can step-and-repeat for different liquids and coating solutions , training new machine-learning models as they go and growing their database of models , ” Luo adds .
Ultimately , the LTMS represents a further signal of intent from Ocean Insight as it seeks to reinforce @ @ @ @ @ @ @ Knowledge Company ” across the photonics value chain – optical components , systems , software and industrial solutions .
“ We are a global optical solutions company – helping research customers to unlock new scientific insights and industry customers to deliver new commercial opportunities , ” notes Scargle .
“ Our scientists and engineers create value in all sorts of ways , ” he concludes , “ whether that ’ s feasibility testing through our lab services group ; machine-learning advances from our Ocean Intelligence group ; or custom product development in our @ @ @ @ @

Ocean Insight’s Liquid Transmission Measurement System (LTMS) provides real-time, in-line monitoring of liquid colouring and coating applications used across the consumer electronics and food processing industries
Optical know-how: an LTMS test assembly at Ocean Insight’s Rochester, NY, development facility. When deployed into an industry setting, the LTMS can generate high-precision colour and concentration measurements on a 24/7 basis. (Courtesy: Ocean Insight)
Ocean Insight, a US manufacturer of specialist spectral systems, software and optical solutions, has high hopes for its Liquid Transmission Measurement System (LTMS), a spectroscopy-based unit for real-time, in-line optical monitoring of liquid concentration levels in a range of industrial plating, colouring and coating applications.
The modular system comprises a rugged optical sensing platform – spectrometer, control unit and machine-learning software – within a compact benchtop configuration that’s suitable for day-to-day deployment into harsh industrial environments. As such, the LTMS is able to generate high-precision colour and concentration measurements from the factory floor on a 24/7 basis, with flow-cell set-up and automatic fluid handling or built-in cuvette holder.
Right now, the LTMS is being sold directly into industry end-users and, once tailored to the customer’s requirements, comes ready to use “out of the box” in the manufacturing facility. “Alternatively, if the end-user has a preferred OEM integrator, the LTMS can be incorporated as part of their existing ‘smart factory system’, with or without fluid-handling capability,” explains Scott Scargle, director of strategic markets at Ocean Insight.
Getting the priorities right
Despite a myriad of potential LTMS applications, Ocean Insight’s near-term focus for the product is in the consumer electronics and food processing industries. Colour consistency of external parts – for Bluetooth speakers, MP3 players and the like – is a major pain-point in the consumer electronics supply chain, with batch-to-batch consistency of anodized aluminium being notoriously difficult to control.
Anodization is an electrolytic process to create a protective, anti-corrosion layer on the aluminium surface – a coating that can subsequently be dyed and decorated in a range of colours. Trouble is, anodization chemistry remains something of a black art, with colour materials and finishing (CMF) designers and contract manufacturers forced to work with wide colour tolerances and complex production processes.
Scott Scargle: “Our scientists and engineers create value in all sorts of ways.” (Courtesy: Ocean Insight)
If that’s the problem, the LTMS looks a lot like the answer. With its ability to measure solution concentrations in the anodization tank out on the factory floor, those CMF tolerances can actually get a lot tighter – which translates into enhanced repeatability, less scrap and streamlined product development cycles. “In short,” notes Scargle, “the LTMS gives the CMF designers a wider colour palette to choose from, while the contract manufacturers can make their parts with better consistency.”
In the food-processing industry, meanwhile, the LTMS is being lined up to support specialist coating applications on a range of foodstuffs. A case in point is the wax coatings that packing-houses apply to citrus fruits – typically to prolong the shelf-life and enhance the visual appeal of the fruit, also to act as a carrier for antifungal agents. “It’s a balancing act,” says Scargle. “The LTMS can be used to make sure concentration levels are within a certain tolerance to meet health and safety requirements, while high enough to maintain a level of effectiveness.”
Another use-case is the application of pesticides to food crops. Before a pesticide mix is applied in the field, for example, the LTMS is able to verify that the concentration falls within a window of acceptance to meet statutory safety guidelines. “Equally important,” adds Scargle, “the LTMS can be used to check the rinse water after the pesticide storage tank is cleaned, ensuring there are no unwanted residuals left behind that may end up being sprayed on crops later.”
Benefits and efficiencies
When it comes to customer upside, one of the big advantages of the LTMS is in-line deployment – a feature that makes it possible to more readily address quality issues as they occur. Consider an aluminium anodization coating tank, the electrolytes of which need to be analysed versus pass/fail criteria on a regular basis. Traditionally that testing has relied on expensive analytical equipment – for example, high-performance liquid chromatography (HPLC) – in a central laboratory (or more often an offsite testing facility for smaller contract manufacturers).
All of which is time-consuming, manually intensive and can mean significant process downtime while the results are pending. “The LTMS essentially eliminates that whole walk-to-lab workflow,” says Lu Luo, sales director at Ocean Insight and head of the company’s development facility in Rochester, New York. “It’s about the benefits of real-time, in-line diagnostics – the workflow and resource efficiencies plus greater process uptime – versus manually intensive and centralized lab testing.” What’s more, the LTMS workflow is such that scientific staff are no longer tied up on routine quality-control tasks. “It’s a portable unit and can be operated from a user-friendly interface by a technician,” Luo adds.
Lu Luo: “The LTMS essentially eliminates that whole walk-to-lab workflow.” (Courtesy: Ocean Insight)
Another notable feature of the LTMS is the innovative use of machine-learning technology. Each customer gets a tailored system that’s “trained” for their specific optical sensing applications versus a number of chemical solutions. “The machine-learning models provide a direct answer on solution concentrations for pass–fail manufacturing decisions – either on the technician’s display or sent digitally to a central manufacturing execution system,” says Luo.
It’s a neat innovation that comes with in-built scalability. “Customers can step-and-repeat for different liquids and coating solutions, training new machine-learning models as they go and growing their database of models,” Luo adds.
Ultimately, the LTMS represents a further signal of intent from Ocean Insight as it seeks to reinforce its credentials as the “Applied Spectral Knowledge Company” across the photonics value chain – optical components, systems, software and industrial solutions. “We are a global optical solutions company – helping research customers to unlock new scientific insights and industry customers to deliver new commercial opportunities,” notes Scargle.
“Our scientists and engineers create value in all sorts of ways,” he concludes, “whether that’s feasibility testing through our lab services group; machine-learning advances from our Ocean Intelligence group; or custom product development in our solutions engineering team.”