Lasers and chemistry reveal how ancient pottery was made -- and how an empire functioned

Peru’s first great empire, the Wari, stretched for more than a thousand miles over the Andes Mountains and along the coast from 600-1000 CE. The pottery they left behind gives archaeologists clues as to how the empire functioned. In a new study in the Journal of Archaeological Science: Reports, researchers showed that rather than using “official” Wari pottery imported from the capital, potters across the empire were creating their own ceramics, decorated to emulate the traditional Wari style. To figure it out, the scientists analyzed the pottery’s chemical make-up, with help from laser beams.

“In this study, we looked at the idea of cosmopolitanism, of incorporating different cultures and practices into a society,” says M. Elizabeth Grávalos, a postdoctoral researcher at the Field Museum in Chicago and the study’s lead author. “We’re trying to show that potters were influenced by the Wari, but this influence was blended with their own local cultural practices.”

Grávalos says this model of cosmopolitanism is a little like trying to replicate a recipe from another culture, but with a local spin. “If you live in the US and you’re making pad thai at home, you might not have access to all the ingredients that someone living in Thailand would have, so you substitute some things,” she says. “Wari ceramics are a little like that — people throughout the empire were interested in Wari material culture, but they weren’t necessarily getting it directly from the Wari heartland. More often than not, we see local people trying to make their own version of Wari pottery.”

Grávalos and her colleagues led archaeological digs throughout Peru, working with local communities to excavate the thousand-year-old remains of households, tombs, and administrative centers, in search of Wari lifeways. The researchers were then granted permission from Peru’s Ministry of Culture to bring samples of ceramics from their excavations to Chicago for analysis.

Clay from different regions has a different chemical makeup, so studying the ceramics’ chemical makeup could tell the researchers if the pots were produced in different places or if they were all imported from the Wari capital.

“We’d take a tiny piece of a pot and used a laser to cut an even tinier piece, basically extracting a piece of the ceramic’s clay paste,” says Grávalos. “Then helium gas carried it to the mass spectrometer, which measures the elements present in the  clay paste.” (The lab set-up didn’t have open laser beams and floating shards of pottery cutting across the room, though — the whole process takes place on a microscopic scale inside a big boxy machine.)

The analysis showed that the pots excavated from distinct regions of Peru have different chemical signatures, and were therefore made with distinct clays. That helps show how the Wari culture spread.

Some empires, like the ancient Romans, took a “top-down” approach to spreading their aesthetic, shipping pottery across the Mediterranean so that people throughout the empire were using the official Roman style. Local potters emulating the traditional Wari style in their own work seems to hint at a more “bottom-up” approach.

“Of course, local people in all empires have some degree of agency and creative control — the only empire that’s truly top-down is the Borg from Star Trek,” says Patrick Ryan Williams, Curator of Archaeological Science and Director of the Elemental Analysis Facility  at the Field Museum and the study’s senior author. “Even the Romans had local people doing things their own way. But what we’re finding in this study is the agency of local peoples and the importance of local economies. In some regions, we find that Wari colonists had their own production centers and were recreating Wari lifeways locally. In other areas, we see that local communities made Wari pottery in their own way. I think that’s what’s really important about this study.”

The researchers say that the patterns revealed by this pottery could help explain why the Wari empire was able to thrive for so long. “Local production, even in a cosmopolitan society with lots of far-flung connections, makes a society more resilient,” says Williams. “If you’re entirely dependent on someone far away sending you things you need, you’re extremely vulnerable.”

Read more at Science Daily

'Life-like' lasers can self-organize, adapt their structure, and cooperate

While many artificial materials have advanced properties, they have a long way to go to combine the versatility and functionality of living materials that can adapt to their situation. For example, in the human body bone and muscle continuously reorganise their structure and composition to better sustain changing weight and level of activity.

Now, researchers from Imperial College London and University College London have demonstrated the first spontaneously self-organising laser device, which can reconfigure when conditions change.

The innovation, reported in Nature Physics, will help enable the development of smart photonic materials capable of better mimicking properties of biological matter, such as responsiveness, adaptation, self-healing, and collective behaviour.

Co-lead author Professor Riccardo Sapienza, from the Department of Physics at Imperial, said: "Lasers, which power most of our technologies, are designed from crystalline materials to have precise and static properties. We asked ourselves if we could create a laser with the ability to blend structure and functionality, to reconfigure itself and cooperate like biological materials do.

"Our laser system can reconfigure and cooperate, thus enabling a first step towards emulating the ever-evolving relationship between structure and functionality typical of living materials."

Lasers are devices that amplify light to produce a special form of light. The self-assembling lasers in the team's experiment consisted of microparticles dispersed in a liquid with high 'gain' -- the ability to amplify light. Once enough of these microparticles collect together, they can harness external energy to 'lase' -- produce laser light.

An external laser was used to heat up a 'Janus' particle (a particle coated on one side with light-absorbing material), around which the microparticles gathered. The lasing created by these microparticle clusters could be turned on and off by changing the intensity of the external laser, which in turn controlled the size and density of the cluster.

The team also showed how the lasing cluster could be transferred in space by heating different Janus particles, demonstrating the adaptability of the system. Janus particles can also collaborate, creating clusters that have properties beyond the simple adding of two clusters, such as changing their shape and boosting their lasing power.

Co-lead author Dr Giorgio Volpe, from the Department of Chemistry at UCL, said: "Nowadays, lasers are used as a matter of course in medicine, telecommunications, and also in industrial production. Embodying lasers with life-like properties will enable the development of robust, autonomous, and durable next-generation materials and devices for sensing applications, non-conventional computing, novel light sources and displays."

Read more at Science Daily

Archaeologists reveal pre-Hispanic cities in Bolivia with laser technology

More than 20 years ago, Dr. Heiko Prümers from the German Archaeological Institute and Prof. Dr. Carla Jaimes Betancourt from the University of Bonn, at that time a student in La Paz, began archaeological excavations on two "mounds" near the village of Casarabe in Bolivia. The Mojos Plains is a southwestern fringe of the Amazon region. Even though the savannah plain, which flooded several months a year during rainy season, does not encourage permanent settlement, there are still many visible traces of the time before Spanish colonization at the beginning of the 16th century. Next to the "mounds," these traces include mainly causeways and canals that often lead for kilometers in a dead straight line across the savannahs.

"This indicated a relatively dense settlement in pre-Hispanic times. Our goal was to conduct basic research and trace the settlements and life there," says Heiko Prümers. In earlier studies, the researchers already found that the Casarabe culture -- named after the nearby village -- dates to the period between 500 and 1400 AD and, according to current knowledge, extended over a region of around 16,000 square kilometers. The "mounds" turned out to be eroded pyramid stumps and platform buildings.

Initial conventional surveys revealed a terraced core area, a ditch-wall enclosing the site, and canals. In addition, it became apparent that some of these pre-Hispanic settlements were enormous in size. "However, the dense vegetation under which these settlements were located prevented us from seeing the structural details of the monumental mounds and their surroundings," says Carla Jaimes Betancourt from the Department for the Anthropology of the Americas at the University of Bonn.

LIDAR technology used in the Amazon for the first time

To find out more, the researchers used the airborne laser technology LIDAR (Light Detection and Ranging) for the first time in the Amazon region. This involves surveying the terrain with a laser scanner attached to a helicopter, small aircraft or drone that transmits around 1.5 million laser pulses per second. In a subsequent evaluation step, the vegetation is digitally removed creating a digital model of the earth's surface, which can also be displayed as a 3D image. "The first results were excellent and showed how effective the technology was even in dense rainforest. From that moment on, the desire arose to map the large settlements of the Casarabe culture using LIDAR technology," says study leader Dr. Heiko Prümers.

For the current study, in 2019 the team together with Prof. Dr. José Iriarte and Mark Robinson from the University of Exeter, mapped a total of 200 square kilometers of the Casarabe cultural area. The evaluation done by the company ArcTron3 held a surprise. What came to light were two remarkably large sites of 147 hectares and 315 hectares in a dense four-tiered settlement system. "With a north-south extension of 1.5 kilometers and an east-west extension of about one kilometer, the largest site found so far is as large as Bonn was in the 17th century," says co-author Prof. Dr. Carla Jaimes Betancourt.

It is not yet possible to estimate how many people lived there. "However, the layout of the settlement itself tells us that planners and many active hands were at work here," says Heiko Prümers. Modifications made to the settlement, for example the expansion of the rampart-ditch system, also speak to a reasonable increase in population. "For the first time, we can refer to pre-Hispanic urbanism in the Amazon and show the map of the Cotoca site, the largest settlement of the Casarabe culture known to us so far," Prümers emphasizes. In other parts of the world similar agrarian cities with low population densities had already been found.

LIDAR shows anthropogenically altered landscape

LIDAR mapping reveals the architecture of the settlement's large squares. Stepped platforms topped by U-shaped structures, rectangular platform mounds, and conical pyramids (up to 22 meters high). Causeway-like paths and canals connect the individual settlements and indicate a tight social fabric. At least one other settlement can be found within five kilometers of each of the settlements known today. "So the entire region was densely settled, a pattern that overturns all previous ideas," says Carla James Betancourt, who is a member of the Transdisciplinary Research Area "Present Pasts" at the University of Bonn.

The researchers emphasize that for all the euphoria about the site mappings and the possibilities they offer for reinterpreting the settlements in their geographic setting, the real archaeological work is just beginning. The goal for the future, they say, is to understand how these large regional centers functioned.

Read more at Science Daily

Astronomers detect 'galactic space laser'

A powerful radio-wave laser, called a 'megamaser', has been observed by the MeerKAT telescope in South Africa.

The record-breaking find is the most distant megamaser of its kind ever detected, at about five billion light years from Earth.

The light from the megamaser has travelled 58 thousand billion billion (58 followed by 21 zeros) kilometres to Earth.

The discovery was made by an international team of astronomers led by Dr Marcin Glowacki, who previously worked at the Inter-University Institute for Data Intensive Astronomy and the University of the Western Cape in South Africa.

Dr Glowacki, who is now based at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Western Australia, said megamasers are usually created when two galaxies violently collide in the Universe.

"When galaxies collide, the gas they contain becomes extremely dense and can trigger concentrated beams of light to shoot out," he said.

"This is the first hydroxyl megamaser of its kind to be observed by MeerKAT and the most distant seen by any telescope to date.

"It's impressive that, with just a single night of observations, we've already found a record-breaking megamaser. It shows just how good the telescope is."

The record-breaking object was named 'Nkalakatha' [pronounced ng-kuh-la-kuh-tah] -- an isiZulu word meaning "big boss."

Dr Glowacki said the megamaser was detected on the first night of a survey involving more than 3000 hours of observations by the MeerKAT telescope.

The team is using MeerKAT to observe narrow regions of the sky extremely deeply and will measure atomic hydrogenin galaxies from the distant past to now. The combination of studying hydroxl masers and hydrogen will help astronomers better understand how the Universe has evolved over time.

"We have follow-up observations of the megamaser planned and hope to make many more discoveries," Dr Glowacki said.

Read more at Science Daily

196 lasers help scientists recreate the conditions inside gigantic galaxy clusters

Galaxies rarely live alone. Instead, dozens to thousands are drawn together by gravity, forming vast clusters that are the largest objects in the universe.

"Galaxy clusters are one of the most awe-inspiring things in the universe," said Prof. Emeritus Don Lamb, a University of Chicago astrophysicist and co-author on a new paper published March 9 -- one that may point the way towards solving a decades-long mystery.

Scientists have long known that the hydrogen gas in galaxy clusters is searingly hot -- about 10 million degrees Kelvin, or roughly the same temperature as the center of the sun -- which is so hot that hydrogen atoms cannot exist. Instead the gas is a plasma consisting of protons and electrons.

But a puzzle persists: There is no straightforward explanation for why or how the gas stays so hot. According to the normal rules of physics, it should have cooled within the age of the universe. But it hasn't.

The challenge for anyone trying to solve this puzzle is that you can't exactly create these kinds of powerfully hot and magnetic conditions in your backyard.

However, there is now one place on Earth where you can: the most energetic laser facility in the world. The National Ignition Facility at Lawrence Livermore National Laboratory is able to create such extreme conditions -- though only for a tiny fraction of a second in a volume the size of a dime.

Scientists from UChicago, the University of Oxford, and the University of Rochester worked together to use the National Ignition Facility -- located in Livermore, California -- to create conditions similar to the hot gas in gigantic galaxy clusters. "The experiments conducted at the NIF are literally out of this world," said Jena Meinecke, who was the first author on the paper.

The scientists focused 196 lasers onto a single tiny target, creating a white-hot plasma with intense magnetic fields that exists for a few billionths of a second.

This was long enough for them to determine that instead of a uniform temperature, there were hot and cold spots in the plasma.

This dovetails with one of the theories that has been proposed for how heat is trapped inside galaxy clusters. Normally, heat would be easily distributed as electrons collide with each other. But the tangled magnetic fields inside the plasma can affect these electrons, causing them to spiral along the direction of magnetic fields -- which can prevent them from evenly distributing and dispersing their energy.

In fact, in the experiment they saw that the conduction of energy was suppressed by more than a factor of 100.

"This is an incredibly exciting result because we've been able to show that what astrophysicists have proposed is on the right track," said Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy and Astrophysics.

"This is indeed an astonishing result," added study co-author University of Rochester Prof. Petros Tzeferacos, who oversaw computer simulations of the complicated experiment. "The simulations were key to untangling the physics at play in the turbulent, magnetized plasma, but the level of thermal transport suppression was beyond what we expected."

The simulations were done with a computer code called the FLASH codes, which was developed at the University of Chicago and is now hosted at the University of Rochester's Flash Center for Computational Science, which is led by Tzeferacos. The code allows scientists to simulate their laser experiments in exquisite detail before they do them, so that they can achieve the results they seek.

This is critical because the scientists only get a precious few shots at the facility -- if something goes wrong, there's no redo. And because the experiment conditions only last nanoseconds, the scientists have to make sure they make the measurements they need at exactly the right time. This means everything has to be precisely plotted out far ahead of time.

"It's a challenge when you're at the very extremes of what can be done, but that's where the frontier is," said Lamb.

More questions remain about the physics of galaxy clusters, however. Though the hot and cold spots are solid evidence for the impact of magnetic fields on the cooling of the hot gas in galaxy clusters, further experiments are needed to understand exactly what is happening. The group is planning its next round of experiments at NIF later this year.

For the moment, though, they're happy to have shed light on why the gas in galaxy clusters is still hot even after billions of years.

Galaxies rarely live alone. Instead, dozens to thousands are drawn together by gravity, forming vast clusters that are the largest objects in the universe.

"Galaxy clusters are one of the most awe-inspiring things in the universe," said Prof. Emeritus Don Lamb, a University of Chicago astrophysicist and co-author on a new paper published March 9 -- one that may point the way towards solving a decades-long mystery.

Scientists have long known that the hydrogen gas in galaxy clusters is searingly hot -- about 10 million degrees Kelvin, or roughly the same temperature as the center of the sun -- which is so hot that hydrogen atoms cannot exist. Instead the gas is a plasma consisting of protons and electrons.

But a puzzle persists: There is no straightforward explanation for why or how the gas stays so hot. According to the normal rules of physics, it should have cooled within the age of the universe. But it hasn't.

The challenge for anyone trying to solve this puzzle is that you can't exactly create these kinds of powerfully hot and magnetic conditions in your backyard.

However, there is now one place on Earth where you can: the most energetic laser facility in the world. The National Ignition Facility at Lawrence Livermore National Laboratory is able to create such extreme conditions -- though only for a tiny fraction of a second in a volume the size of a dime.

Scientists from UChicago, the University of Oxford, and the University of Rochester worked together to use the National Ignition Facility -- located in Livermore, California -- to create conditions similar to the hot gas in gigantic galaxy clusters. "The experiments conducted at the NIF are literally out of this world," said Jena Meinecke, who was the first author on the paper.

The scientists focused 196 lasers onto a single tiny target, creating a white-hot plasma with intense magnetic fields that exists for a few billionths of a second.

This was long enough for them to determine that instead of a uniform temperature, there were hot and cold spots in the plasma.

This dovetails with one of the theories that has been proposed for how heat is trapped inside galaxy clusters. Normally, heat would be easily distributed as electrons collide with each other. But the tangled magnetic fields inside the plasma can affect these electrons, causing them to spiral along the direction of magnetic fields -- which can prevent them from evenly distributing and dispersing their energy.

In fact, in the experiment they saw that the conduction of energy was suppressed by more than a factor of 100.

"This is an incredibly exciting result because we've been able to show that what astrophysicists have proposed is on the right track," said Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy and Astrophysics.

"This is indeed an astonishing result," added study co-author University of Rochester Prof. Petros Tzeferacos, who oversaw computer simulations of the complicated experiment. "The simulations were key to untangling the physics at play in the turbulent, magnetized plasma, but the level of thermal transport suppression was beyond what we expected."

The simulations were done with a computer code called the FLASH codes, which was developed at the University of Chicago and is now hosted at the University of Rochester's Flash Center for Computational Science, which is led by Tzeferacos. The code allows scientists to simulate their laser experiments in exquisite detail before they do them, so that they can achieve the results they seek.

This is critical because the scientists only get a precious few shots at the facility -- if something goes wrong, there's no redo. And because the experiment conditions only last nanoseconds, the scientists have to make sure they make the measurements they need at exactly the right time. This means everything has to be precisely plotted out far ahead of time.

"It's a challenge when you're at the very extremes of what can be done, but that's where the frontier is," said Lamb.

More questions remain about the physics of galaxy clusters, however. Though the hot and cold spots are solid evidence for the impact of magnetic fields on the cooling of the hot gas in galaxy clusters, further experiments are needed to understand exactly what is happening. The group is planning its next round of experiments at NIF later this year.

Read more at Science Daily

Ultrashort-pulse lasers kill bacterial superbugs, spores

Life-threatening bacteria are becoming ever more resistant to antibiotics, making the search for alternatives to antibiotics an increasingly urgent challenge. For certain applications, one alternative may be a special type of laser.

Researchers at Washington University School of Medicine in St. Louis have found that lasers that emit ultrashort pulses of light can kill multidrug-resistant bacteria and hardy bacterial spores. The findings, available online in the Journal of Biophotonics, open up the possibility of using such lasers to destroy bacteria that are hard to kill by other means. The researchers previously have shown that such lasers don't damage human cells, making it possible to envision using the lasers to sterilize wounds or disinfect blood products.

"The ultrashort-pulse laser technology uniquely inactivates pathogens while preserving human proteins and cells," said first author Shaw-Wei (David) Tsen, MD, PhD, an instructor of radiology at Washington University's Mallinckrodt Institute of Radiology (MIR). "Imagine if, prior to closing a surgical wound, we could scan a laser beam across the site and further reduce the chances of infection. I can see this technology being used soon to disinfect biological products in vitro, and even to treat bloodstream infections in the future by putting patients on dialysis and passing the blood through a laser treatment device."

Tsen and senior author Samuel Achilefu, PhD, the Michel M. Ter-Pogossian Professor of Radiology and director of MIR's Biophotonics Research Center, have been exploring the germicidal properties of ultrashort-pulse lasers for years. They have shown that such lasers can inactivate viruses and ordinary bacteria without harming human cells. In the new study, conducted in collaboration with Shelley Haydel, PhD, a professor of microbiology at Arizona State University, they extended their exploration to antibiotic-resistant bacteria and bacterial spores.

The researchers trained their lasers on multidrug-resistant Staphylococcus aureus (MRSA), which causes infections of the skin, lungs and other organs, and extended spectrum beta-lactamase-producing Escherichia coli (E. coli), which cause urinary tract infections, diarrhea and wound infections. Apart from their shared ability to make people miserable, MRSA and E. coli are very different types of bacteria, representing two distant branches of the bacterial kingdom. The researchers also looked at spores of the bacterium Bacillus cereus, which causes food poisoning and food spoilage. Bacillus spores can withstand boiling and cooking.

In all cases, the lasers killed more than 99.9% of the target organisms, reducing their numbers by more than 1,000 times.

Viruses and bacteria contain densely packed protein structures that can be excited by an ultrashort-pulse laser. The laser kills by causing these protein structures to vibrate until some of their molecular bonds break. The broken ends quickly reattach to whatever they can find, which in many cases is not what they had been attached to before. The result is a mess of incorrect linkages inside and between proteins, and that mess causes normal protein function in microorganisms to grind to a halt.

"We previously published a paper in which we showed that the laser power matters," Tsen said. "At a certain laser power, we're inactivating viruses. As you increase the power, you start inactivating bacteria. But it takes even higher power than that, and we're talking orders of magnitude, to start killing human cells. So there is a therapeutic window where we can tune the laser parameters such that we can kill pathogens without affecting the human cells."

Heat, radiation and chemicals such as bleach are effective at sterilizing objects, but most are too damaging to be used on people or biological products. By inactivating all kinds of bacteria and viruses without damaging cells, ultrashort-pulse lasers could provide a new approach to making blood products and other biological products safer.

Read more at Science Daily

Pulsed lasers in liquids speed up hunt for effective catalysts

Chemical catalysts are the change agents behind the production of just about everything we use in our daily lives, from plastics to prescription drugs. When the right catalysts are mixed with the right chemical compounds, molecules that would otherwise take years to interact do so in mere seconds.

However, developing even one catalyst material to trigger this precise choreography of atoms can take months, even years, when using traditional wet chemistry procedures that use only chemical reactions, often in the liquid phase, to grow nanoparticles.

University of Rochester researchers say there is a way to shorten that process dramatically -- by instead using pulsed lasers in liquids to quickly create carefully tuned, systematic arrays of nanoparticles that can be easily compared and tested for use as catalysts.

The process is described in a Chemical Reviews article by Astrid Müller, an assistant professor of chemical engineering at the University of Rochester who has adapted the technique for her work on sustainable energy solutions. Three PhD students in her lab -- coauthors Ryland Forsythe, Connor Cox, and Madeleine Wilsey -- conducted an exhaustive review of almost 600 previous papers involving the use of pulsed lasers in liquids. As a result, their article is the most comprehensive, up-to-date survey of a technology that was first developed in 1987.

Pulsed lasers in liquids an 'indispensable tool' for discovering catalysts

So how does pulsed-laser-in-liquid synthesis work?
 

• A pulsed laser is directed at a solid material immersed in liquid. This creates a high-temperature, high-pressure plasma near the surface of the solid.
• As the plasma decays, it vaporizes molecules in the surrounding liquid, leading to a cavitation bubble. Within the bubble, chemical reactions begin to occur between particles from the liquid and particles that were ablated, or knocked loose, from the solid.
• After periodic expansions and contractions, the cavitation bubble violently implodes, causing shock waves and rapid cooling. Nanoparticles from the bubble condense in small clusters that are injected into the surrounding liquid and become stable.

The pulsed-laser-in-liquids technique offers multiple advantages over traditional wet-lab synthesis of nanomaterials. According to Müller:
 

• Because the reactions are confined primarily within the cavitation bubble, the resulting nanoparticles have remarkably uniform properties. "Every particle that is made is created under the same conditions," she says.
• The properties of the nanoparticles can be easily fine-tuned by adjusting the laser pulses and the chemical compositions of the solid and surrounding fluid.
• Laser-made nanocatalysts are intrinsically more active than those obtained by wet chemistry methods. Metastable nanomaterials with non-equilibrium structures and compositions can easily be produced. Such materials cannot be made under moderate temperatures and pressures.
• Laser synthesis can be controlled remotely, increasing the potential for large-scale industrial applications.
• Pulsed-laser-in-liquids synthesis of nanomaterials is also far more rapid than traditional methods. The technique can prepare bulk quantities of a nanoparticle in an hour or less. Systematic arrays of 70 materials can be made in a week.

"These advantages make this an indispensable as a tool for discovery," says Müller, whose background includes work in lasers, materials, and electrocatalysis. "You often have people who know lasers and materials, or maybe electrocatalysis and materials, but you very rarely get someone with expertise in all three."

She says, "This is what compelled us to write this paper, because the Müller group can bring together the perspectives of all three fields."

How catalysts can combat climate change

While working as a staff scientist at Caltech, Müller pioneered an adaption of the laser-in-liquids technique to prepare nonprecious water-splitting electrocatalysts that liberate oxygen from water to produce clean hydrogen. At Rochester, the Müller group expands on her expertise to study laser-made electrocatalysts as a way to turn climate-damaging carbon dioxide (CO2) into a closed cycle of useful liquid fuels, such as methanol or ethanol.

"If you were to burn these fuels again, you make CO2 again, so you go round and round. The carbon always stays within the cycle, and does not contribute to more climate change," Müller says. "For that to work we need catalysts, and no one knows yet what those catalysts would be -- what would work and why, and why other catalysts don't work."

Hence her interest in using pulsed-laser-in-liquid synthesis to accelerate the process. "It is hugely important because we can't just sit and hope for the best with climate change; we need to work on successor technologies now," she says.

So far, pulsed-laser-in-liquid synthesis has had only limited commercial use. The start-up cost of investing in laser technology is a stumbling block for many companies, Müller says. "But that will change as this method gets more and more traction," she believes.

Read more at Science Daily

The paradox of a free-electron laser without the laser

A new way of producing coherent light in the ultra-violet spectral region, which points the way to developing brilliant table-top x-ray sources, has been produced in research led at the University of Strathclyde.

The scientists have developed a type of ultra-short wavelength coherent light source that does not require laser action to produce coherence. Common electron-beam based light sources, known as fourth-generation light sources, are based on the free-electron laser (FEL), which uses an undulator to convert electron beam energy into X-rays.

Coherent light sources are powerful tools that enable research in many areas of medicine, biology, material sciences, chemistry and physics.

This new way of producing coherent radiation could revolutionise light sources, as it would make them highly compact, essentially table-top size, and capable of producing ultra-short duration pulses of light, much shorter than can be produced easily by any other means.

Making ultraviolet and X-ray coherent light sources more widely available would transform the way science is done; a university could have one of the devices in a single room, on a table top, for a reasonable price.

The group is now planning a proof-of-principle experiment in the ultraviolet spectral range to demonstrate this new way of producing coherent light. If successful, it should dramatically accelerate the development of even shorter wavelength coherent sources based on the same principle. The Strathclyde group has set up a facility to investigate these types of sources: the Scottish Centre for the Application of Plasma-based Accelerators (SCAPA), which hosts one of the highest power lasers in the UK.

The new research has been published in Scientific Reports, one of the Nature family of journals.

Professor Dino Jaroszynski, of Strathclyde's Department of Physics, led the research. He said: "This work significantly advances the state-of-the-art of synchrotron sources by proposing a new method of producing short-wavelength coherent radiation, using a short undulator and attosecond duration electron bunches.

"This is more compact and less demanding on the electron beam quality than free-electron lasers and could provide a paradigm shift in light sources, which would stimulate a new direction of research. It proposes to use bunch compression -- as in chirped pulse amplification lasers -- within the undulator to significantly enhance the radiation brightness.

"The new method presented would be of wide interest to a diverse community developing and using light sources."

In FELs, as in all lasers, the intensity of light is amplified by a feedback mechanism that locks the phases of individual radiators, which in this case are "free" electrons. In the FEL, this is achieved by passing a high energy electron beam through the undulator, which is an array of alternating polarity magnets.

Light emitted from the electrons as they wiggle through the undulator creates a force called the ponderomotive force that bunches the electrons -- some are slowed down, some are sped up, which causes bunching, similar to traffic on a motorway periodically slowing and speeding up.

Electrons passing through the undulator radiate incoherent light if they are uniformly distributed -- for every electron that emits light, there is another electron that partially cancels out the light because they radiate out of phase. An analogy of this partial cancelling out is rain on the sea: it produces many small ripples that partially cancel each other out, effectively quelling the waves -- reducing their amplitude. In contrast, steady or pulsating wind will cause the waves to amplify through the mutual interaction of the wind with the sea.

In the FEL, electron bunching causes amplification of the light and the increase in its coherence, which usually takes a long time -- thus very long undulators are required. In an X-ray FEL, the undulators can be more than a hundred metres long. The accelerators driving these X-ray FELs are kilometres long, which makes these devices very expensive and some of the largest instruments in the world.

However, using a free-electron laser to produce coherent radiation is not the only way; a "pre-bunched" beam or ultra-short electron bunch can also be used to achieve exactly the same coherence in a very short undulator that is less than a metre in length. As long as the electron bunch is shorter than the wavelength of the light produced by the undulator, it will automatically produce coherent light -- all the light waves will add up or interfere constructively, which leads to very brilliant light with exactly the same properties of light from a laser.

Read more at Science Daily

Liquid water at 170 degrees Celsius

 Using the X-ray laser European XFEL, a research team has investigated how water heats up under extreme conditions. In the process, the scientists were able to observe water that remained liquid even at temperatures of more than 170 degrees Celsius. The investigation revealed an anomalous dynamic behaviour of water under these conditions. The results of the study, which are published in the Proceedings of the National Academy of Sciences (PNAS), are of fundamental importance for the planning and analysis of investigations of sensitive samples using X-ray lasers.

European XFEL, an international research facility, which extends from the DESY site in Hamburg to the neighbouring town of Schenefeld in Schleswig-Holstein, is home to the most powerful X-ray laser in the world. It can generate up to 27,000 intense X-ray flashes per second. For their experiments, the researchers used series of 120 flashes each. The individual flashes were less than a millionth of a second apart (exactly 0.886 microseconds). The scientists sent these pulse trains into a thin, water-filled quartz glass tube and observed the reaction of the water.

"We asked ourselves how long and how strongly water can be heated in the X-ray laser and whether it still behaves like water," explains lead author Felix Lehmkühler from DESY. "For example, does it still function as a coolant at high temperatures?" A detailed understanding of superheated water is also essential for a large number of investigations on heat-sensitive samples, such as polymers or biological samples.

"With the X-ray flashes, we were able to heat the water up to 172 degrees Celsius within a ten thousandth of a second without it evaporating," reports Lehmkühler. Such a boiling delay can normally only be observed up to about 110 degrees Celsius. "But that is not the only anomalous feature," the physicist emphasises. The scientists investigated the movement of silicon nanospheres floating in the water as markers for the dynamics in the sample. "In the extremely overheated water, we observed that the movement of silicon dioxide nanospheres deviated significantly from the expected random Brownian molecular movement. This indicates an uneven heating of the sample," says Lehmkühler. Existing theoretical models cannot yet satisfactorily explain this behaviour because they are not designed for water under these extreme conditions.

Thanks to the rapid flash sequence of the European XFEL, the researchers were able to observe the process in extreme detail. "What makes the European XFEL unique is the high repetition rate, that is, the high number of pulses per second," explains co-author Adrian Mancuso, head of the SPB/SFX instrument at the European XFEL where the experiments took place. "And we have all the instrumentation in place -- such as fast cameras, diagnostics and more -- to make these experiments possible." For instance, the Adaptive Gain Integrating Pixel Detector (AGIPD) developed by a DESY-led consortium can take around 350 serial images at intervals of only 220 billionths of a second (nanoseconds).

This setup not only allowed the superheated water to be generated, but also enabled the scientists to carry out precisely controlled series of experiments with X-ray flashes of reduced intensity. "Using silicon filters, we fine-tuned the energy of the pulses so that we were able to control exactly how much the water was heated," reports Lehmkühler. "For example, we were able to determine how strong the X-ray flashes should be so that the temperature of an aqueous sample remains more or less constant."

This enables researchers to better plan experiments with heat-sensitive samples at the X-ray laser, for example. On the other hand, the heating effect can also be used in a targeted manner if its exact course is known. The team plans to further investigate these effects also within the framework of the Centre for Molecular Water Science (CMWS), which is currently being set up at DESY.

Read more at Science Daily

How to have a blast like a black hole

 Laser Engineering at Osaka University have successfully used short, but extremely powerful laser blasts to generate magnetic field reconnection inside a plasma. This work may lead to a more complete theory of X-ray emission from astronomical objects like black holes.

In addition to being subjected to extreme gravitational forces, matter being devoured by a black hole can be also be pummeled by intense heat and magnetic fields. Plasmas, a fourth state of matter hotter than solids, liquids, or gasses, are made of electrically charged protons and electrons that have too much energy to form neutral atoms. Instead, they bounce frantically in response to magnetic fields. Within a plasma, magnetic reconnection is a process in which twisted magnetic field lines suddenly "snap" and cancel each other, resulting in the rapid conversion of magnetic energy into particle kinetic energy. In stars, including our sun, reconnection is responsible for much of the coronal activity, such as solar flares. Owing to the strong acceleration, the charged particles in the black hole's accretion disk emit their own light, usually in the X-ray region of the spectrum.

To better understand the process that gives rise to the observed X-rays coming from black holes, scientists at Osaka University used intense laser pulses to create similarly extreme conditions on the lab. "We were able to study the high-energy acceleration of electrons and protons as the result of relativistic magnetic reconnection," Senior author Shinsuke Fujioka says. "For example, the origin of emission from the famous black hole Cygnus X-1, can be better understood."

This level of light intensity is not easily obtained, however. For a brief instant, the laser required two petawatts of power, equivalent to one thousand times the electric consumption of the entire globe. With the LFEX laser, the team was able to achieve peak magnetic fields with a mind-boggling 2,000 telsas. For comparison, the magnetic fields generated by an MRI machine to produce diagnostic images are typically around 3 teslas, and Earth's magnetic field is a paltry 0.00005 teslas. The particles of the plasma become accelerated to such an extreme degree that relativistic effects needed to be considered.

"Previously, relativistic magnetic reconnection could only be studied via numerical simulation on a supercomputer. Now, it is an experimental reality in a laboratory with powerful lasers," first author King Fai Farley Law says. The researchers believe that this project will help elucidate the astrophysical processes that can happen at places in the Universe that contain extreme magnetic fields.

From Science Daily

Face shield or face mask to stop the spread of COVID-19?

 If the United States Centers for Disease Control and Prevention (CDC) guidelines aren't enough to convince you that face shields alone shouldn't be used to stop the spread of COVID-19, then maybe a new visualization study will.

To increase public awareness about the effectiveness of face shields alone as well as face masks with exhalation valves, researchers from Florida Atlantic University's College of Engineering and Computer Science used qualitative visualizations to test how face shields and masks with valves perform in impeding the spread of aerosol-sized droplets. Widespread public use of these alternatives to regular masks could potentially have an adverse effect on mitigation efforts.

For the study, just published in the journal Physics of Fluids, researchers employed flow visualization in a laboratory setting using a laser light sheet and a mixture of distilled water and glycerin to generate the synthetic fog that made up the content of a cough-jet. They visualized droplets expelled from a mannequin's mouth while simulating coughing and sneezing. By placing a plastic face shield and an N95-rated face mask with a valve, they were able to map out the paths of droplets and demonstrate how they performed.

Results of the study show that although face shields block the initial forward motion of the jet, the expelled droplets move around the visor with relative ease and spread out over a large area depending on light ambient disturbances. Visualizations for the face mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control.

"From this latest study, we were able to observe that face shields are able to block the initial forward motion of the exhaled jet, however, aerosolized droplets expelled with the jet are able to move around the visor with relative ease," said Manhar Dhanak, Ph.D., department chair, professor, and director of SeaTech, who co-authored the paper with Siddhartha Verma, Ph.D., lead author and an assistant professor; and John Frankenfeld, a technical professional, all within FAU's Department of Ocean and Mechanical Engineering. "Over time, these droplets can disperse over a wide area in both lateral and longitudinal directions, albeit with decreasing droplet concentration."

To demonstrate the performance of the face shield, researchers used a horizontal laser sheet in addition to a vertical laser sheet revealing how the droplets cross the horizontal plane. Not only did the researchers observe forward spread of the droplets, they found that droplets also spread in the reverse direction. Notably, face shields impede forward motion of the exhaled droplets to some extent, and masks with valves do so to an even lesser extent. However, once released into the environment, the aerosol-sized droplets get dispersed widely depending on light ambient disturbances.

Like the N-95-rated face mask used in this study, other types of masks such as certain cloth-based masks that are available commercially also come equipped with one to two exhale ports, located on either side of the facemask. The N95-rated face mask with the exhale valve used in this study had a small amount of exhaled droplets that escaped from the gap between the top of the mask and the bridge of the nose. Moreover, the exhalation port significantly reduced the effectiveness of the mask as a means of source control, as a large number of droplets passed through the valve unfiltered and unhindered.

"There is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields as well as using masks that are equipped with exhalation valves," said Verma. "A driving factor for this increased adoption is better comfort compared to regular masks. However, face shields have noticeable gaps along the bottom and the sides, and masks with exhalation ports include a one-way valve which restricts airflow when breathing in, but allows free outflow of air. The inhaled air gets filtered through the mask material, but the exhaled breath passes through the valve unfiltered."

The researchers say that the key takeaway from this latest study illustrates that face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolized droplets. Despite the increased comfort that these alternatives offer, they say it may be preferable to use well-constructed, high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves. Widespread public adoption of the alternatives, in lieu of regular masks, could potentially have an adverse effect on ongoing mitigation efforts against COVID-19.

Read more at Science Daily

New class of laser beam doesn't follow normal laws of refraction

 University of Central Florida researchers have developed a new type of laser beam that doesn't follow long-held principles about how light refracts and travels.

The findings, which were published recently in Nature Photonics, could have huge implications for optical communication and laser technologies.

"This new class of laser beams has unique properties that are not shared by common laser beams," says Ayman Abouraddy, a professor in UCF's College of Optics and Photonics and the study's principal investigator.

The beams, known as spacetime wave packets, follow different rules when they refract, that is when they pass through different materials. Normally, light slows down when it travels into a denser material.

"In contrast, spacetime wave packets can be arranged to behave in the usual manner, to not change speed at all, or even to anomalously speed up in denser materials," Abouraddy says. "As such, these pulses of light can arrive at different points in space at the same time."

"Think about how a spoon inside a water-filled glass looks broken at the point where the water and air meet," Abouraddy says. "The speed of light in air is different from the speed of light in water. And so, the light rays wind up bending after they cross the surface between air to water, and so apparently the spoon looks bent. This is a well-known phenomenon described by Snell's Law."

Although Snell's Law still applies, the underlying change in velocity of the pulses is no longer applicable for the new laser beams, Abouraddy says. These abilities are counter to Fermat's Principle that says light always travels such that it takes the shortest path, he says.

"What we find here, though, is no matter how different the materials are that light passes through, there always exists one of our spacetime wave packets that could cross the interface of the two materials without changing its velocity," Abouraddy says. "So, no matter what the properties of the medium are, it will go across the interface and continue as if it's not there."

For communication, this means the speed of a message traveling in these packets is no longer affected by traveling through different materials of different densities.

"If you think of a plane trying to communicate with two submarines at the same depth but one is far away and the other one's close by, the one that's farther away will incur a longer delay than the one that's close by," Abouraddy says. "We find that we can arrange for our pulses to propagate such that they arrive at the two submarines at the same time. In fact, now the person sending the pulse doesn't even need to know where the submarine is, as long as they are at the same depth. All those submarines will receive the pulse at the same time so you can blindly synchronize them without knowing where they are."

Abouraddy's research team created the spacetime wave packets by using a device known as a spatial light modulator to reorganize the energy of a pulse of light so that its properties in space and time are no longer separate. This allows them to control the "group velocity" of the pulse of light, which is roughly the speed at which the peak of the pulse travels.

Previous work has shown the team's ability to control the group velocity of the spacetime wave packets, including in optical materials. The current study built upon that work by finding they could also control the spacetime wave packets' speed through different media. This does not contradict special relativity in any way, because it applies to the propagation of the pulse peak rather than to the underlying oscillations of the light wave.

"This new field that we're developing is a new concept for light beams," Abouraddy says. "As a result, everything we look into using these beams reveals new behavior. All the behavior we know about light really takes tacitly an underlying presumption that its properties in space and time are separable. So, all we know in optics is based on that. It's a built-in assumption. It's taken to be the natural state of affairs. But now, breaking that underlying assumption, we're starting to see new behavior all over the place."

Co-authors of the study were Basanta Bhaduri, lead author and a former research scientist with UCF's College of Optics and Photonics, now with Bruker Nano Surfaces in California, and Murat Yessenov, a doctoral candidate in the college.

Bhaduri became interested in Abouraddy's research after reading about it in journals, such as Optics Express and Nature Photonics, and joined the professor's research team in 2018. For the study, he helped develop the concept and designed the experiments, as well as carried out measurements and analyzed data.

He says the study results are important in many ways, including the new research avenues it opens.

"Space-time refraction defies our expectations derived from Fermat's principle and offers new opportunities for molding the flow of light and other wave phenomena," Bhaduri says.

Yessenov's roles included data analysis, derivations and simulations. He says he became interested in the work by wanting to explore more about entanglement, which in quantum systems is when two well-separated objects still have a relation to each other.

"We believe that spacetime wave packets have more to offer and many more interesting effects can be unveiled using them," Yessenov says.

Read more at Science Daily

Now metal surfaces can be instant bacteria killers

Bacterial pathogens can live on surfaces for days. What if frequently touched surfaces such as doorknobs could instantly kill them off?

Purdue University engineers have created a laser treatment method that could potentially turn any metal surface into a rapid bacteria killer -- just by giving the metal's surface a different texture.

In a study published in the journal Advanced Materials Interfaces, the researchers demonstrated that this technique allows the surface of copper to immediately kill off superbugs such as MRSA.

"Copper has been used as an antimicrobial material for centuries. But it typically takes hours for native copper surfaces to kill off bacteria," said Rahim Rahimi, a Purdue assistant professor of materials engineering.

"We developed a one-step laser-texturing technique that effectively enhances the bacteria-killing properties of copper's surface."

The technique is not yet tailored to killing viruses such as the one responsible for the COVID-19 pandemic, which are much smaller than bacteria.

Since publishing this work, however, Rahimi's team has begun testing this technology on the surfaces of other metals and polymers that are used to reduce risks of bacterial growth and biofilm formation on devices such as orthopedic implants or wearable patches for chronic wounds.

Giving implants an antimicrobial surface would prevent the spread of infection and antibiotic resistance, Rahimi said, because there wouldn't be a need for antibiotics to kill off bacteria from an implant's surface.

The technique might apply to metallic alloys that also are known to have antimicrobial properties.

Metals such as copper normally have a really smooth surface, which makes it difficult for the metal to kill bacteria by contact.

The technique developed by Rahimi's team uses a laser to create nanoscale patterns on the metal's surface. The patterns produce a rugged texture that increases surface area, allowing more opportunity for bacteria to hit the surface and rupture on the spot.

Researchers in the past have used various nanomaterial coatings to enhance the antimicrobial properties of metal surfaces, but these coatings are prone to leach off and can be toxic to the environment.

"We've created a robust process that selectively generates micron and nanoscale patterns directly onto the targeted surface without altering the bulk of the copper material," said Rahimi, whose lab develops innovative materials and biomedical devices to address health care challenges.

The laser-texturing has a dual effect: The technique not only improves direct contact, but also makes a surface more hydrophilic. For orthopedic implants, such a surface allows bone cells to more strongly attach, improving how well the implant integrates with bone. Rahimi's team observed this effect with fibroblast cells.

Read more at Science Daily

Using lasers to visualize molecular mysteries in our atmosphere

Invisible to the human eye, molecular interactions between gases and liquids underpin much of our lives, including the absorption of oxygen molecules into our lungs, many industrial processes and the conversion of organic compounds within our atmosphere. But difficulties in measuring gas-liquid collisions have so far prevented the fundamental exploration of these processes.

Kenneth McKendrick and Matthew Costen, both at Heriot-Watt University, in Edinburgh, U.K., hope their new technique of enabling the visualization of gas molecules bouncing off a liquid surface will help climate scientists improve their predictive atmospheric models. The technique is described in The Journal of Chemical Physics, from AIP Publishing.

"The molecule of interest in our study, the hydroxyl radical, is an unstable fragment of a molecule that affects the whole of the understanding of atmospheric chemistry and things that genuinely affect climate," said McKendrick. "Some of these important OH reactions take place at the surface of liquid droplets, but we can't see surface interactions directly, so we measure the characteristics of the scattered molecules from real-time movies to infer what happened during their encounter with the liquid."

Laser sheets are the key to the technique, inducing a short-lived fluorescent signal from each molecule as it passes through 10 nanosecond pulses. Laser-induced fluorescence isn't new in itself, but this was the first time laser sheets have been applied to scattering from a surface in a vacuum with no other molecules present to interfere with the scattering from the molecular beam. This enabled the McKendrick team to capture individual frames of molecular movement, from molecular beam to liquid surface and scattering, which were compiled into movies.

Unlike previous methods of capturing gas-liquid interactions, all the characteristics needed to understand the interaction -- speed, scatter angle, rotation, etc. -- are captured within the simple movies that McKendrick describes as "intuitive." By observing the molecular film strips, McKendrick's team noted molecules scattered at a broad range of angles, similar to a ball bouncing off in all directions when thrown onto an uneven surface. This simple observation directly proved the surface of liquids is not flat.

"When you get down to the molecular level, the surface of these liquids is very rough, so much so that you can barely tell the difference between the distribution of molecules when directed down vertically onto the surface or when at an angle of 45 degrees. This finding is important for understanding the chances of different molecular processes happening at the liquid surface," said McKendrick.

Read more at Science Daily

Airborne lidar system poised to improve accuracy of climate change models

Researchers have developed a laser-based system that can be used for airborne measurement of important atmospheric gases with unprecedented accuracy and resolution. The ability to collect this data will help scientists better understand how these atmospheric gases affect the climate and could help improve climate change predictions.

In the Optical Society journal Applied Optics, researchers from Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) -- Germany's national center for aerospace, energy and transportation research -- describe how their lidar instrument was used aboard an aircraft to acquire the first simultaneous measurements of the vertical structure of water vapor and ozone in the tropopause region of the atmosphere. The researchers say that the new system might even be useful for monitoring atmospheric gases from space.

The tropopause separates the surface-based troposphere layer where weather takes place from the overlying stratosphere that contains the ozone layer that protects life on Earth from harmful radiation. Scientists want to study water vapor and ozone in the tropopause because the distribution of these atmospheric gases in this layer plays a crucial role in the Earth's climate.

"The ability to detect the vertical structure of water vapor and ozone is critical for understanding the exchange of these atmospheric gases between the troposphere and the stratosphere," said Andreas Fix, who led the research team. "These measurements could help us identify errors and uncertainties in climate models that would help improve predictions of the future climate, which is one of the central challenges for our society and economy."

Gaining a 3D perspective

Atmospheric gases can be assessed with instruments flown into the atmosphere or with data acquired from satellites. However, these methods haven't been able to provide a full picture of atmospheric gas distribution because they either lack the vertical component or don't provide high enough resolution. Although instruments carried with balloons -- known as balloon sondes -- can provide highly resolved vertical profiles they don't offer detailed temporal resolution and can only be used at selected sites.

To solve these problems, the researchers developed a lidar system that uses laser light to measure both ozone and water vapor at the same time. Their approach, called differential absorption lidar (DIAL), uses two slightly different UV wavelengths to measure each gas. The UV radiation at one wavelength is mostly absorbed by the gas molecules while most of the other wavelength is reflected. Measuring the ratio of the UV signals returning from the atmosphere allows calculation of a detailed gas profile.

The gas profiles created using the new lidar system exhibit a vertical resolution of around 250 meters and a horizontal resolution of about 10 kilometers below the aircraft's flight track.

"This vertical capability is a significant advancement in studying exchange processes at the tropopause," said Fix. "It helps overcome significant shortcomings in resolving the fine-scale distribution that have made it difficult to understand processes responsible for exchange at the tropopause."

Achieving energy efficiency

To perform this method aboard a plane, the researchers used a highly efficient optical parametric oscillator (OPO) they previously developed to convert the laser output to the UV wavelengths needed to measure water vapor and ozone. "The conversion needs to be very energy efficient to generate UV radiation with adequate pulse energies and high average power from the limited energy available on board an aircraft," explained Fix.

Tests of the new lidar system showed that its accuracy matched well with that of balloon sondes. In 2017, the researchers flew the new system aboard the wave-driven isentropic exchange (WISE) mission, which involved multiple long-range flights over the North Atlantic and Northern Europe. They found that the instrument worked remarkably well, remained stable during use and could measure characteristic ozone and water vapor distributions at the tropopause.

Read more at Science Daily

A new way of diagnosing and treating disease -- without cutting skin

Laser light

University of British Columbia researchers have developed a specialized microscope that has the potential ability to both diagnose diseases that include skin cancer and perform incredibly precise surgery -- all without cutting skin.

The researchers describe the technology in a study published today in Science Advances.

"Our technology allows us to scan tissue quickly, and when we see a suspicious or abnormal cell structure, we can perform ultra-precise surgery and selectively treat the unwanted or diseased structure within the tissue -- without cutting into the skin," said Yimei Huang, co-lead author of the study and a former postdoctoral fellow at the department of dermatology and skin science at UBC and BC Cancer.

Huang co-led the study with Zhenguo Wu, a UBC PhD student.

The device is a specialized type of multiphoton excitation microscope that allows imaging of living tissue up to about one millimeter in depth using an ultrafast infrared laser beam. What sets the researchers' microscope apart from previous technology is that it's capable of not only digitally scanning living tissue, but also treating the tissue by intensifying the heat produced by the laser.

When applied to treating diseases of the skin, the microscope allows medical professionals to pinpoint the exact location of the abnormality, diagnose it and treat it instantly. It could be used to treat any structure of the body that is reached by light and that requires extremely precise treatment, including nerves or blood vessels in the skin, eye, brain or other vital structures.

"We can alter the pathway of blood vessels without impacting any of the surrounding vessels or tissues," said study co-author Harvey Lui, professor at the department of dermatology and skin science at UBC and the Vancouver Coastal Health Research Institute, and a dermatologist at BC Cancer. "For diagnosing and scanning diseases like skin cancer, this could be revolutionary."

The researchers wanted to make multiphoton microscope technology more versatile while also increasing its precision.

"We wanted to be able to identify what was happening under the skin from many different angles and to have the capability of imaging different body sites," said senior author Haishan Zeng, professor of dermatology, pathology and physics at UBC and distinguished scientist with BC Cancer.

"Once we achieved that, we wondered whether we could transform this diagnostic device into a treatment device by simply turning up the power of the laser."

The results were incredibly exciting.

"We are not only the first to achieve fast video-rate imaging that enables clinical applications, but also the first to develop this technology for therapeutic uses," said Zeng.

The researchers have partnered with several UBC departments, including mechanical engineering, electrical engineering and ophthalmology, to develop different versions of the technology. Exploration includes research into the development of a miniature version that could be used to perform microscopic examinations and treatment during endoscopy -- a non-surgical procedure used to examine a person's digestive tract using an endoscope, a flexible tube with a light and camera attached to it.

Read more at Science Daily

The first laser radio transmitter

This device uses a frequency comb laser to emit and modulate microwaves wirelessly. The laser uses different frequencies of light beating together to generate microwave radiation. The researchers used this phenomenon to send a song wirelessly to a receiver.

You've never heard Dean Martin like this.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences transmitted a recording of Martin's classic "Volare" wirelessly via a semiconductor laser -- the first time a laser has been used as a radio frequency transmitter.

In a paper published in the Proceedings of the National Academy of Sciences, the researchers demonstrated a laser that can emit microwaves wirelessly, modulate them, and receive external radio frequency signals.

"The research opens the door to new types of hybrid electronic-photonic devices and is the first step toward ultra-high-speed Wi-Fi," said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, at SEAS and senior author of the study.

This research builds on previous work from the Capasso Lab. In 2017, the researchers discovered that an infrared frequency comb in a quantum cascade laser could be used to generate terahertz frequencies, the submillimeter wavelengths of the electromagnetic spectrum that could move data hundreds of times faster than today's wireless platforms. In 2018, the team found that quantum cascade laser frequency combs could also act as integrated transmitters or receivers to efficiently encode information.

Now, the researchers have figured out a way to extract and transmit wireless signals from laser frequency combs.

Unlike conventional lasers, which emit a single frequency of light, laser frequency combs emit multiple frequencies simultaneously, evenly spaced to resemble the teeth of a comb. In 2018, the researchers discovered that inside the laser, the different frequencies of light beat together to generate microwave radiation. The light inside the cavity of the laser caused electrons to oscillate at microwave frequencies -- which are within the communications spectrum.

"If you want to use this device for Wi-Fi, you need to be able to put useful information in the microwave signals and extract that information from the device," said Marco Piccardo, a postdoctoral fellow at SEAS and first author of the paper.

The first thing the new device needed to transmit microwave signals was an antenna. So, the researchers etched a gap into the top electrode of the device, creating a dipole antenna (like the rabbit ears on the top of an old TV). Next, they modulated the frequency comb to encode information on the microwave radiation created by the beating light of the comb. Then, using the antenna, the microwaves are radiated out from the device, containing the encoded information. The radio signal is received by a horn antenna, filtered and sent to a computer.

The researchers also demonstrated that the laser radio could receive signals. The team was able to remotely control the behavior of the laser using microwave signals from another device.

"This all-in-one, integrated device holds great promise for wireless communication," said Piccardo. "While the dream of terahertz wireless communication is still a ways away, this research provides a clear roadmap showing how to get there."

The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.

Read more at Science Daily

New form of laser for sound

The optical laser has grown to a $10 billion global technology market since it was invented in 1960, and has led to Nobel prizes for Art Ashkin for developing optical tweezing and Gerard Mourou and Donna Strickland for work with pulsed lasers. Now a Rochester Institute of Technology researcher has teamed up with experts at the University of Rochester to create a different kind of laser -- a laser for sound, using the optical tweezer technique invented by Ashkin.

In the newest issue of Nature Photonics, the researchers propose and demonstrate a phonon laser using an optically levitated nanoparticle. A phonon is a quantum of energy associated with a sound wave and optical tweezers test the limits of quantum effects in isolation and eliminates physical disturbances from the surrounding environment. The researchers studied the mechanical vibrations of the nanoparticle, which is levitated against gravity by the force of radiation at the focus of an optical laser beam.

"Measuring the position of the nanoparticle by detecting the light it scatters, and feeding that information back into the tweezer beam allows us to create a laser-like situation," said Mishkat Bhattacharya, associate professor of physics at RIT and a theoretical quantum optics researcher. "The mechanical vibrations become intense and fall into perfect sync, just like the electromagnetic waves emerging from an optical laser."

Because the waves emerging from a laser pointer are in sync, the beam can travel a long distance without spreading in all directions -- unlike light from the sun or from a light bulb. In a standard optical laser the properties of the light output are controlled by the material from which the laser is made. Interestingly, in the phonon laser the roles of light and matter are reversed -- the motion of the material particle is now governed by the optical feedback.

"We are very excited to see what the uses of this device are going to be -- especially for sensing and information processing given that the optical laser has so many, and still evolving, applications," said Bhattacharya. He also said the phonon laser promises to enable the investigation of fundamental quantum physics, including engineering of the famous thought experiment of Schrödinger's cat, which can exist at two places simultaneously.

From Science Daily

Next up: Ultracold simulators of super-dense stars

Rice University graduate student Tom Langin makes an adjustment to an experiment that uses 10 lasers of varying wavelengths to laser-cool ions in a neutral plasma.

Rice University physicists have created the world's first laser-cooled neutral plasma, completing a 20-year quest that sets the stage for simulators that re-create exotic states of matter found inside Jupiter and white dwarf stars.

The findings are detailed this week in the journal Science and involve new techniques for laser cooling clouds of rapidly expanding plasma to temperatures about 50 times colder than deep space.

"We don't know the practical payoff yet, but every time physicists have laser cooled a new kind of thing, it has opened a whole world of possibilities," said lead scientist Tom Killian, professor of physics and astronomy at Rice. "Nobody predicted that laser cooling atoms and ions would lead to the world's most accurate clocks or breakthroughs in quantum computing. We do this because it's a frontier."

Killian and graduate students Tom Langin and Grant Gorman used 10 lasers of varying wavelengths to create and cool the neutral plasma. They started by vaporizing strontium metal and using one set of intersecting laser beams to trap and cool a puff of strontium atoms about the size of a child's fingertip. Next, they ionized the ultracold gas with a 10-nanosecond blast from a pulsed laser. By stripping one electron from each atom, the pulse converted the gas to a plasma of ions and electrons.

Energy from the ionizing blast causes the newly formed plasma to expand rapidly and dissipate in less than one thousandth of a second. This week's key finding is that the expanding ions can be cooled with another set of lasers after the plasma is created. Killian, Langin and Gorman describe their techniques in the new paper, clearing the way for their lab and others to make even colder plasmas that behave in strange, unexplained ways.

Plasma is an electrically conductive mix of electrons and ions. It is one of four fundamental states of matter; but unlike solids, liquids and gases, which are familiar in daily life, plasmas tend to occur in very hot places like the surface of the sun or a lightning bolt. By studying ultracold plasmas, Killian's team hopes to answer fundamental questions about how matter behaves under extreme conditions of high density and low temperature.

To make its plasmas, the group starts with laser cooling, a method for trapping and slowing particles with intersecting laser beams. The less energy an atom or ion has, the colder it is, and the slower it moves about randomly. Laser cooling was developed in the 1990s to slow atoms until they are almost motionless, or just a few millionths of a degree above absolute zero.

"If an atom or ion is moving, and I have a laser beam opposing its motion, as it scatters photons from the beam it gets momentum kicks that slow it," Killian said. "The trick is to make sure that light is always scattered from a laser that opposes the particle's motion. If you do that, the particle slows and slows and slows."

During a postdoctoral fellowship at the National Institute of Standards and Technology in Bethesda, Md., in 1999, Killian pioneered the ionization method for creating neutral plasma from a laser-cooled gas. When he joined Rice's faculty the following year, he started a quest for a way to make the plasmas even colder. One motivation was to achieve "strong coupling," a phenomenon that happens naturally in plasmas only in exotic places like white dwarf stars and the center of Jupiter.

"We can't study strongly coupled plasmas in places where they naturally occur," Killian said. "Laser cooling neutral plasmas allows us to make strongly coupled plasmas in a lab, so that we can study their properties"

"In strongly coupled plasmas, there is more energy in the electrical interactions between particles than in the kinetic energy of their random motion," Killian said. "We mostly focus on the ions, which feel each other, and rearrange themselves in response to their neighbors' positions. That's what strong coupling means."

Because the ions have positive electric charges, they repel one another through the same force that makes your hair stand up straight if it gets charged with static electricity.

"Strongly coupled ions can't be near one another, so they try to find equilibrium, an arrangement where the repulsion from all of their neighbors is balanced," he said. "This can lead to strange phenomena like liquid or even solid plasmas, which are far outside our normal experience."

In normal, weakly coupled plasmas, these repulsive forces only have a small influence on ion motion because they're far outweighed by the effects of kinetic energy, or heat.

"Repulsive forces are normally like a whisper at a rock concert," Killian said. "They're drowned out by all the kinetic noise in the system."

In the center of Jupiter or a white dwarf star, however, intense gravity squeezes ions together so closely that repulsive forces, which grow much stronger at shorter distances, win out. Even though the temperature is quite high, ions become strongly coupled.

Killian's team creates plasmas that are orders of magnitude lower in density than those inside planets or dead stars, but by lowering the temperature they raise the ratio of electric-to-kinetic energies. At temperatures as low as one-tenth of a Kelvin above absolute zero, Killian's team has seen repulsive forces take over.

"Laser cooling is well developed in gases of neutral atoms, for example, but the challenges are very different in plasmas," he said.

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Nobel Prize in Physics 2018

Laser beam light effect

The inventions being honored this year have revolutionised laser physics. Extremely small objects and incredibly rapid processes are now being seen in a new light. Advanced precision instruments are opening up unexplored areas of research and a multitude of industrial and medical applications.

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2018 "for groundbreaking inventions in the field of laser physics" with one half to Arthur Ashkin, Bell Laboratories, Holmdel, USA "for the optical tweezers and their application to biological systems" and the other half jointly to Gérard Mourou, École Polytechnique, Palaiseau, France and University of Michigan, Ann Arbor, USA and Donna Strickland, University of Waterloo, Canada "for their method of generating high-intensity, ultra-short optical pulses."

Arthur Ashkin invented optical tweezers that grab particles, atoms, viruses and other living cells with their laser beam fingers. This new tool allowed Ashkin to realise an old dream of science fiction -- using the radiation pressure of light to move physical objects. He succeeded in getting laser light to push small particles towards the centre of the beam and to hold them there. Optical tweezers had been invented.

A major breakthrough came in 1987, when Ashkin used the tweezers to capture living bacteria without harming them. He immediately began studying biological systems and optical tweezers are now widely used to investigate the machinery of life.

Gérard Mourou and Donna Strickland paved the way towards the shortest and most intense laser pulses ever created by humankind. Their revolutionary article was published in 1985 and was the foundation of Strickland's doctoral thesis.

Using an ingenious approach, they succeeded in creating ultrashort high-intensity laser pulses without destroying the amplifying material. First they stretched the laser pulses in time to reduce their peak power, then amplified them, and finally compressed them. If a pulse is compressed in time and becomes shorter, then more light is packed together in the same tiny space -- the intensity of the pulse increases dramatically.

Strickland and Mourou's newly invented technique, called chirped pulse amplification, CPA, soon became standard for subsequent high-intensity lasers. Its uses include the millions of corrective eye surgeries that are conducted every year using the sharpest of laser beams.

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