To the general public, lasers heat objects. And generally, that would be correct.

But lasers also show promise to do quite the opposite — to cool materials. Lasers that can cool materials could revolutionize fields ranging from bio-imaging to quantum communication.

In 2015, 91̽�� researchers announced that they can use a laser to cool water and other liquids below room temperature. Now that same team has used a similar approach to refrigerate something quite different: a solid semiconductor. As the team shows in a published June 23 in Nature Communications, they could use an infrared laser to cool the solid semiconductor by at least 20 degrees C, or 36 F, below room temperature.

The device is a — similar to a diving board. Like a diving board after a swimmer jumps off into the water, the cantilever can vibrate at a specific frequency. But this cantilever doesn’t need a diver to vibrate. It can oscillate in response to thermal energy, or heat energy, at room temperature. Devices like these could make ideal optomechanical sensors, where their vibrations can be detected by a laser. But that laser also heats the cantilever, which dampens its performance.

“Historically, the laser heating of nanoscale devices was a major problem that was swept under the rug,” said senior author , a 91̽��professor of materials science and engineering and a senior scientist at the Pacific Northwest National Laboratory. “We are using infrared light to cool the resonator, which reduces interference or ‘noise’ in the system. This method of solid-state refrigeration could significantly improve the sensitivity of optomechanical resonators, broaden their applications in consumer electronics, lasers and scientific instruments, and pave the way for new applications, such as photonic circuits.”

The team is the first to demonstrate “solid-state laser refrigeration of nanoscale sensors,” added Pauzauskie, who is also a faculty member at the 91̽�� and the 91̽��.

The results have wide potential applications due to both the improved performance of the resonator and the method used to cool it. The vibrations of semiconductor resonators have made them useful as mechanical sensors to detect acceleration, mass, temperature and other properties in a variety of electronics — such as accelerometers to detect the direction a smartphone is facing. Reduced interference could improve performance of these sensors. In addition, using a laser to cool the resonator is a much more targeted approach to improve sensor performance compared to trying to cool an entire sensor.

In their experimental setup, a tiny ribbon, or nanoribbon, of cadmium sulfide extended from a block of silicon — and would naturally undergo thermal oscillation at room temperature.

At the end of this diving board, the team placed a tiny ceramic crystal containing a specific type of impurity, ytterbium ions. When the team focused an infrared laser beam at the crystal, the impurities absorbed a small amount of energy from the crystal, causing it to glow in light that is shorter in wavelength than the laser color that excited it. This “blueshift glow” effect cooled the ceramic crystal and the semiconductor nanoribbon it was attached to.

“These crystals were carefully synthesized with a specific concentration of ytterbium to maximize the cooling efficiency,” said co-author , a 91̽��doctoral student in molecular engineering.

The researchers used two methods to measure how much the laser cooled the semiconductor. First, they observed changes to the oscillation frequency of the nanoribbon.

“The nanoribbon becomes more stiff and brittle after cooling — more resistant to bending and compression. As a result, it oscillates at a higher frequency, which verified that the laser had cooled the resonator,” said Pauzauskie.

The team also observed that the light emitted by the crystal shifted on average to longer wavelengths as they increased laser power, which also indicated cooling.

Using these two methods, the researchers calculated that the resonator’s temperature had dropped by as much as 20 degrees C below room temperature. The refrigeration effect took less than 1 millisecond and lasted as long as the excitation laser was on.

“In the coming years, I will eagerly look to see our laser cooling technology adapted by scientists from various fields to enhance the performance of quantum sensors,” said lead author , a 91̽��doctoral student in materials science and engineering.

Researchers say the method has other potential applications. It could form the heart of highly precise scientific instruments, using changes in oscillations of the resonator to accurately measure an object’s mass, such as a single virus particle. Lasers that cool solid components could also be used to develop cooling systems that keep key components in electronic systems from overheating.

, 91̽��professor emeritus of chemical engineering, is an additional co-author. The research was funded by the Air Force Office of Scientific Research, the National Science Foundation, the National Institutes of Health and the UW.

For more information, contact Pauzauskie at peterpz@uw.edu.

Now imagine construction at a smaller scale — less than 1/100th the thickness of a piece of paper. This is the nanoscale. It is the scale at which scientists are working to develop potentially groundbreaking technologies in fields like . It is also a scale where traditional fabrication methods simply will not work. Our standard tools, even miniaturized, are too bulky and too corrosive to reproducibly manufacture components at the nanoscale.

Researchers at the 91̽�� have developed a method that could make reproducible manufacturing at the nanoscale possible. The team adapted a light-based technology employed widely in biology — known as optical traps or — to operate in a water-free liquid environment of carbon-rich organic solvents, thereby enabling new potential applications.

As the team reports in a published Oct. 30 in the journal Nature Communications, the optical tweezers act as a light-based “” that can assemble nanoscale semiconductor materials precisely into larger structures. Unlike the tractor beams of science fiction, which grab spaceships, the team employs the optical tweezers to trap materials that are nearly one billion times shorter than a meter.

“This is a new approach to nanoscale manufacturing,” said co-senior author , a 91̽��associate professor of materials science and engineering, faculty member at the and the , and a senior scientist at the . “There are no chamber surfaces involved in the manufacturing process, which minimizes the formation of strain or other defects. All of the components are suspended in solution, and we can control the size and shape of the nanostructure as it is assembled piece by piece.”

“Using this technique in an organic solvent allows us to work with components that would otherwise degrade or corrode on contact with water or air,” said co-senior author , a 91̽��assistant professor of chemical engineering and faculty member in the and the Molecular Engineering & Sciences Institute. “Organic solvents also help us to superheat the material we’re working with, allowing us to control material transformations and drive chemistry.”

To demonstrate the potential of this approach, the researchers used the optical tweezers to build a novel nanowire heterostructure, which is a nanowire consisting of distinct sections comprised of different materials. The starting materials for the nanowire heterostructure were shorter “nanorods” of crystalline germanium, each just a few hundred nanometers long and tens of nanometers in diameter — or about 5,000 times thinner than a human hair. Each is capped with a metallic bismuth nanocrystal.

The researchers then used the light-based “tractor beam” to grab one of the germanium nanorods. Energy from the beam also superheats the nanorod, melting the bismuth cap. They then guide a second nanorod into the “tractor beam” and — thanks to the molten bismuth cap at the end — solder them end-to-end. The researchers could then repeat the process until they had assembled a patterned nanowire heterostructure with repeating semiconductor-metal junctions that was five-to-ten times longer than the individual building blocks.

“We’ve taken to calling this optically oriented assembly process ‘photonic nanosoldering’ — essentially soldering two components together at the nanoscale using light,” said Holmberg.

Nanowires that contain junctions between materials — such as the germanium-bismuth junctions synthesized by the 91̽��team — may eventually be a route to creating topological for applications in quantum computing.

The tractor beam is actually a highly focused laser that creates a type of optical trap, a pioneered by Arthur Ashkin in the 1970s. To date, optical traps have been used almost exclusively in water- or vacuum-based environments. Pauzauskie’s and Holmberg’s teams adapted optical trapping to work in the more volatile environment of organic solvents.

“Generating a stable optical trap in any type of environment is a delicate balancing act of forces, and we were lucky to have two very talented graduate students working together on this project,” said Holmberg.

The photons that make up the laser beam generate a force on objects in the immediate vicinity of the optical trap. The researchers can adjust the laser’s properties so that the force generated can either trap or release an object, be it a single germanium nanorod or a longer nanowire.

“This is the kind of precision needed for reliable, reproducible nanofabrication methods, without chaotic interactions with other surfaces or materials that can introduce defects or strain into nanomaterials,” said Pauzauskie.

The researchers believe that their nanosoldering approach could enable additive manufacturing of nanoscale structures with different sets of materials for other applications.

“We hope that this demonstration results in researchers using optical trapping for the manipulation and assembly of a wider set of nanoscale materials, irrespective of whether or not those materials happen to be compatible with water,” said Holmberg.

Co-lead authors on the paper are Elena Pandres, a 91̽��graduate student in chemical engineering, and Matthew Crane, a 91̽��doctoral graduate and current postdoctoral researcher in the 91̽��Department of Chemistry. Co-author is E. James Davis, a 91̽��professor emeritus of chemical engineering. The research was funded by the National Science Foundation, the 91̽��Molecular Engineering Materials Center, the 91̽��Molecular Engineering & Sciences Institute, the 91̽��Institute for Nano-engineered Systems, the 91̽��Clean Energy Institute, the State of Washington, the Washington Research Foundation and the Air Force Office of Scientific Research.

For more information, contact Pauzauskie at peterpz@uw.edu and Holmberg at holmvc@uw.edu.

Scientists are excited about diamonds — not the types that adorn jewelry, but the microscopic variety that are less than the width of a human hair. These so-called “nanodiamonds” are made up almost entirely of carbon. But by introducing other elements into the nanodiamond’s crystal lattice — a method known as “doping” — researchers could produce traits useful in medical research, computation and beyond.

In a published May 3 in , researchers at the 91̽��, and announced that they can use extremely high pressure and temperature to dope nanodiamonds. The team used this approach to dope nanodiamonds with silicon, causing the diamonds to glow a deep red — a property that would make them useful for cell and tissue imaging.

The team discovered that their method could also dope nanodiamonds with , a and nonreactive element related to helium found in balloons. Nanodiamonds doped with such elements could be applied to — a rapidly expanding field that includes quantum communication and quantum computing.

“Our approach lets us intentionally dope other elements within diamond nanocrystals by carefully selecting the molecular starting materials used during their synthesis,” said corresponding author , a 91̽��associate professor of materials science and engineering and researcher at the Pacific Northwest National Laboratory.

There are other methods to dope nanodiamonds, such as ion implantation, but this process often damages the crystal structure and the introduced elements are placed randomly, which limits performance and applications. Here, the researchers decided not to dope the nanodiamonds after they had been synthesized. Instead, they doped the molecular ingredients to make nanodiamonds with the element they wanted to introduce, then used high temperature and pressure to synthesize nanodiamonds with the included elements.

In principle, it’s like making a cake: It is far simpler and more effective to add sugar to the batter, rather than trying to add sugar to the cake after baking.

The team’s starting point for nanodiamonds was a carbon-rich material — similar to charcoal, said Pauzauskie — which the researchers spun into a lightweight, porous matrix known as an . They then doped the carbon aerogel with a silicon-containing molecule called , which was chemically integrated within the carbon aerogel. The researchers sealed the reactants within the gasket of a diamond anvil cell, which could generate pressures as high as 15 gigapascals inside the gasket. For reference, 1 gigapascal is roughly 10,000 atmospheres of pressure, or 10 times the pressure at the deepest part of the ocean.

To prevent the aerogel from being crushed at such extreme pressures, they used argon, which becomes solid at 1.8 gigapascals, as a pressure medium. After loading the material to high pressure, the researchers used a above 3,100 F, more than one-third the surface temperature of the sun. In collaboration with , a 91̽��professor emeritus of chemical engineering, they saw that at these temperatures the solid argon melts to form a supercritical fluid.

Through this process, the carbon aerogel was converted into nanodiamonds containing luminescent point defects formed from the silicon-based dopant molecules. The nanodiamonds emitted a deep-red light at a wavelength of about 740 nanometers, which is useful in medical imaging. Nanodiamonds doped with other elements could emit other colors.

“We can throw a dart at the and — so long as the element we hit is soluble in diamond — we could incorporate it deliberately into the nanodiamond using this method,” said Pauzauskie, who is also a researcher with the 91̽�� and the . “You could make a wide spectrum of nanodiamonds that emit different colors for imaging purposes. We may also be able to use this molecular doping approach to make more complex point defects with two or more different dopant atoms, including completely new defects that have not been created before.”

Surprisingly, the researchers discovered that their nanodiamonds also contained two other elements that they didn’t intend to introduce — the argon used as a pressure medium and nitrogen from the air. Just like the silicon that the researchers had intended to introduce, the nitrogen and argon atoms had been fully incorporated into the nanodiamond’s crystal structure.

This marks the first time scientists have used high-temperature, high-pressure assembly to introduce a element — argon — into a nanodiamond lattice structure. It is not easy to force nonreactive atoms to associate with other materials in a compound.

“This was serendipitous, a complete surprise,” said Pauzauskie. “But the fact that argon was incorporated into the nanodiamonds means that this method is potentially useful to create other point defects that have potential for use in quantum information science research.”

Researchers hope next to dope nanodiamonds intentionally with , another noble gas, for possible use in fields such as quantum communications and quantum sensing.

Finally, the team’s method also could help solve a cosmic mystery: Nanodiamonds have been found in outer space, and something out there — such as supernovae or high-energy collisions — dopes them with noble gases. Though the methods developed by Pauzauskie and his team are for doping nanodiamonds here on Earth, their findings could help scientists learn which types of extraterrestrial events trigger cosmic doping far from home.

Lead author on the paper is , a former doctoral student in Pauzauskie’s laboratory and now a postdoctoral researcher in the 91̽��Department of Chemistry. Co-authors are former 91̽��postdoctoral researcher , now at the University of Napoli Federico II in Italy; doctoral student and professor in the 91̽��Department of Chemistry; former Department of Materials Science & Engineering doctoral students , now a postdoctoral researcher at Sandia National Laboratories, and , now a hardware system reliability engineer at Apple; and , head of the Nanoscale Materials Section at the Naval Research Laboratory. The research was funded by the National Science Foundation, the 91̽��, the U.S. Office of Naval Research, the Microanalysis Society of America and the Pacific Northwest National Laboratory.

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For more information, contact Pauzauskie at peterpz@uw.edu and Crane at +1 206-616-8754 or mjcrane@uw.edu. Pauzauskie is on sabbatical in Europe.

Grant numbers: DMR-1555007, CHE-1565520, CHE-1464497, DMR-171997

But to realize these applications, supercapacitors need better electrodes, which connect the supercapacitor to the devices that depend on their energy. These electrodes need to be both quicker and cheaper to make on a large scale and also able to charge and discharge their electrical load faster. A team of engineers at the 91̽�� thinks they’ve come up with a process for manufacturing supercapacitor electrode materials that will meet these stringent industrial and usage demands.

The researchers, led by 91̽��assistant professor of materials science and engineering , published a on July 17 in the journal describing their supercapacitor electrode and the fast, inexpensive way they made it. Their novel method starts with carbon-rich materials that have been dried into a low-density matrix called an aerogel. This aerogel on its own can act as a crude electrode, but Pauzauskie’s team more than doubled its capacitance, which is its ability to store electric charge.

These inexpensive starting materials, coupled with a streamlined synthesis process, minimize two common barriers to industrial application: cost and speed.

“In industrial applications, time is money,” said Pauzauskie. “We can make the starting materials for these electrodes in hours, rather than weeks. And that can significantly drive down the synthesis cost for making high-performance supercapacitor electrodes.”

Effective supercapacitor electrodes are synthesized from carbon-rich materials that also have a high surface area. The latter requirement is critical because of the unique way supercapacitors store electric charge. While a conventional battery stores electric charges via the chemical reactions occurring within it, a supercapacitor instead stores and separates positive and negative charges directly on its surface.

“Supercapacitors can act much faster than batteries because they are not limited by the speed of the reaction or byproducts that can form,” said co-lead author , a 91̽��doctoral student in the Department of Materials Science & Engineering. “Supercapacitors can charge and discharge very quickly, which is why they’re great at delivering these ‘pulses’ of power.”

“They have great applications in settings where a battery on its own is too slow,” said fellow lead author , a doctoral student in the 91̽��Department of Chemical Engineering. “In moments where a battery is too slow to meet energy demands, a supercapacitor with a high surface area electrode could ‘kick’ in quickly and make up for the energy deficit.”

To get the high surface area for an efficient electrode, the team used aerogels. These are wet, gel-like substances that have gone through a special treatment of drying and heating to replace their liquid components with air or another gas. These methods preserve the gel’s 3-D structure, giving it a high surface area and extremely low density. It’s like removing all the water out of Jell-O with no shrinking.

“One gram of aerogel contains about as much surface area as one football field,” said Pauzauskie.

Crane made aerogels from a gel-like polymer, a material with repeating structural units, created from formaldehyde and other carbon-based molecules. This ensured that their device, like today’s supercapacitor electrodes, would consist of carbon-rich materials.

Previously, Lim that adding graphene — which is a sheet of carbon just one atom thick — to the gel imbued the resulting aerogel with supercapacitor properties. But, Lim and Crane needed to improve the aerogel’s performance, and make the synthesis process cheaper and easier.

In Lim’s previous experiments, adding graphene hadn’t improved the aerogel’s capacitance. So they instead loaded aerogels with thin sheets of either molybdenum disulfide or tungsten disulfide. Both chemicals are used widely today in industrial lubricants.

The researchers treated both materials with high-frequency sound waves to break them up into thin sheets and incorporated them into the carbon-rich gel matrix. They could synthesize a fully-loaded wet gel in less than two hours, while other methods would take many days. After obtaining the dried, low-density aerogel, they combined it with adhesives and another carbon-rich material to create an industrial “dough,” which Lim could simply roll out to sheets just a few thousandths of an inch thick. They cut half-inch discs from the dough and assembled them into simple coin cell battery casings to test the material’s effectiveness as a supercapacitor electrode.

Not only were their electrodes fast, simple and easy to synthesize, but they also sported a capacitance at least 127 percent greater than the carbon-rich aerogel alone.

Lim and Crane expect that aerogels loaded with even thinner sheets of molybdenum disulfide or tungsten disulfide — theirs were about 10 to 100 atoms thick — would show an even better performance. But first, they wanted to show that loaded aerogels would be faster and cheaper to synthesize, a necessary step for industrial production. The fine-tuning comes next.

The team believes that these efforts can help advance science even outside the realm of supercapacitor electrodes. Their aerogel-suspended molybdenum disulfide might remain sufficiently stable to catalyze hydrogen production. And their method to trap materials quickly in aerogels could be applied to high capacitance batteries or catalysis.

Co-author was doctoral student Xuezhe Zhou in the Department of Materials Science & Engineering. The research was conducted with the help of , a 91̽��start-up company based in Seattle that was recently acquired by BASF. The research was funded by the 91̽��and the . Pauzauskie is also affiliated with the Fundamental and Computational Sciences Directorate at the Pacific Northwest National Laboratory.

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For more information, contact Pauzauskie at peterpz@uw.edu or 206-543-2303.

91̽�� scientists are participating in three of these endeavors, known as Multidisciplinary University Research Initiative (MURI) grants. One, an effort to , is a collaboration among five universities led by 91̽��electrical engineering professor . 91̽��professors Peter Pauzauskie and Alberto Aliseda are part of two other MURI-funded efforts to develop innovative approaches to cutting-edge fields of engineering.

Cool ideas for lasers

In the Department of Materials Science & Engineering, assistant professor and his team have their eyes focused on laser innovations. Last year they an approach to cooling liquids using laser light. Now, as part of a MURI grant led by Mansoor Sheik-Bahae at the University of New Mexico, Pauzauskie’s research group is joining a larger collaboration to develop self-cooling lasers. Their efforts would address a major limitation in today’s laser technology.

“Because of the heat they generate, every laser based on optical fibers will melt down at high operating powers,” said Pauzauskie. “As a result, today we have to either limit the power at which lasers operate or accept that they’ll eventually burn out.”

But new laser designs using self-cooling materials could operate at a much higher powers. 91̽��is one of four universities collaborating on this MURI grant, and they hope to create a prototype self-cooling laser that is significantly more powerful than what’s possible today.

In a laser pointer, a battery generates an electric current, which is converted into laser light through a semiconductor crystal. Researchers have also shown it is possible to amplify the power of conventional lasers by “stretching” laser materials into long optical fibers.

But even these devices are limited by the heat they generate. The MURI team will investigate materials that could both protect the fibers from mechanical damage and actively cool them as they operate. That, Pauzauskie says, could unlock a number of new applications for laser technologies, such as cutting and processing industrial materials or launching micro-satellites to remote parts of the solar system using the “radiation pressure” of light.

Out of the $7.5 million MURI grant to be shared among the five participating institutions, Pauzauskie’s group will receive $1.3 million over five years for experiments, equipment and personnel.

“I was over the moon to hear that we got the MURI grant,” said Pauzauskie. “This support will make it possible to bring at least three new graduate students or post-docs to our materials-science team to work specifically on this project.”

Spray secrets

Over in the Department of Mechanical Engineering, associate professor expressed similar elation. He and are part of a separate $7.5 million MURI collaboration among scientists at five universities to control the tiny liquid droplets that make up sprays.

“We want to take concepts from different approaches and disciplines and bring them together to address fundamental problems in controlling sprays,” said Aliseda. “Sprays form in many fast-moving liquids, and we want to control the droplets when they form and keep them from causing disruptions.”

While the sprays from ocean waves and spray bottles are generally harmless, sprays disrupt mechanical systems that depend on the reliable, predictable flow of liquids. Jet engines can stall if liquid fuel is injected improperly.

Led by Olivier Desjardins at Cornell University, the team wants to build upon past research in spray formation and apply that knowledge toward practical devices that can control the size and distribution of droplets in sprays.

One practical route for controlling sprays is the atomizer, the device that a liquid passes through to form a spray. Researchers can manipulate droplet size and concentration by modifying the atomizer’s design, such as the size of the injection needles. But the MURI team wants to explore other avenues to control the spray.

“We also want to take existing designs and modify their control, such as varying the pressure of the liquid or using acoustics or electrostatic forces to control spray droplets once they’re generated,” said Aliseda.

The team’s approaches will also include new sensors to monitor droplets and computational simulations of different sprays. The microscopic scale of manipulation they seek could increase control of liquid systems in a variety of settings, from diesel engines to ship wakes. Aliseda and his 91̽��team will receive $2.2 million over five years. Like Pauzauskie, he plans to recruit and hire several researchers to work on this project.

“People have been thinking about these ideas for over 50 years,” said Aliseda. “What we’re trying to do is to advance the state of the science and technology so we can reach manufacturers soon through better and more practical scientific practices.”

And that is precisely what the MURI grants are designed to do.

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For more information, contact Pauzauskie at 206-543-2303 or peterpz@uw.edu and Aliseda at 206-543-4910 or aaliseda@uw.edu.

But those concentrated beams of light have never been able to cool liquids. 91̽�� researchers are the first to solve a decades-old puzzle — figuring out how to make a laser refrigerate water and other liquids under real-world conditions.

In a published online Nov. 20 in the , the team used an infrared laser to cool water by about 36 degrees Fahrenheit — a major breakthrough in the field.

“Typically, when you go to the movies and see Star Wars laser blasters, they heat things up. This is the first example of a laser beam that will refrigerate liquids like water under everyday conditions,” said senior author , 91̽��assistant professor of materials science and engineering. “It was really an open question as to whether this could be done because normally water warms when illuminated.”

The discovery could help industrial users “point cool” tiny areas with a focused point of light. Microprocessors, for instance, might someday use a laser beam to cool specific components in computer chips to prevent overheating and enable more efficient information processing.

Scientists could also use a laser beam to precisely cool a portion of a cell as it divides or repairs itself, essentially slowing these rapid processes down and giving researchers the opportunity to see how they work. Or they could cool a single neuron in a network — essentially silencing without damaging it — to see how its neighbors bypass it and rewire themselves.

“There’s a lot of interest in how cells divide and how molecules and enzymes function, and it’s never been possible before to refrigerate them to study their properties,” said Pauzauskie, who is also a scientist at the U.S. Department of Energy’s in Richland, Washington. “Using laser cooling, it may be possible to prepare slow-motion movies of life in action. And the advantage is that you don’t have to cool the entire cell, which could kill it or change its behavior.”

The 91̽��team chose infrared light for its cooling laser with biological applications in mind, as visible light could give cells a damaging “sunburn.” They demonstrated that the laser could refrigerate saline solution and cell culture media that are commonly used in genetic and molecular research.

To achieve the breakthrough, the 91̽��team used a material commonly found in commercial lasers but essentially ran the laser phenomenon in reverse. They illuminated a single microscopic crystal suspended in water with infrared laser light to excite a unique kind of glow that has slightly more energy than that amount of light absorbed.

This higher-energy glow carries heat away from both the crystal and the water surrounding it. The laser refrigeration process was first demonstrated in vacuum conditions at Los Alamos National Laboratory in 1995, but it has taken nearly 20 years to demonstrate this process in liquids.

Typically, growing laser crystals is an expensive process that requires lots of time and can cost thousands of dollars to produce just a single gram of material. The 91̽��team demonstrated that a low-cost hydrothermal process can be used to manufacture a well-known laser crystal for laser refrigeration applications in a faster, inexpensive and scalable way.

The 91̽��team also designed an instrument that uses a laser trap — akin to a microscopic tractor beam — to “hold” a single nanocrystal surrounded by liquid in a chamber and illuminate it with the laser. To determine whether the liquid is cooling, the instrument also projects the particle’s “shadow” in a way that allows the researchers to observe minute changes in its motion.

As the surrounding liquid cools, the trapped particle slows down, allowing the team to clearly observe the refrigerating effect. They also designed the crystal to change from a blueish-green to a reddish-green color as it cools, like a built-in color thermometer.

“The real challenge of the project was building an instrument and devising a method capable of determining the temperature of these nanocrystals using signatures of the same light that was used to trap them,” said lead author , who recently received his doctorate from the 91̽��in materials science and engineering and now works at Intel Corp.

So far, the 91̽��team has only demonstrated the cooling effect with a single nanocrystal, as exciting multiple crystals would require more laser power. The laser refrigeration process is currently quite energy intensive, Pauzauskie said, and future steps include looking for ways to improve its efficiency.

One day the cooling technology itself might be used to enable higher-power lasers for manufacturing, telecommunications or defense applications, as higher-powered lasers tend to overheat and melt down.

“Few people have thought about how they could use this technology to solve problems because using lasers to refrigerate liquids hasn’t been possible before,” he said. “We are interested in the ideas other scientists or businesses might have for how this might impact their basic research or bottom line.”

The research was funded by the Air Force Office of Scientific Research and the UW, and benefitted from additional support from the National Science Foundation, Lawrence Livermore National Laboratory and Pacific Northwest National Laboratory.

Co-authors include 91̽��doctoral students in chemistry, in materials science and engineering and in chemical engineering.

For more information, contact Pauzauskie at peterpz@uw.edu or 206-543-2303.