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  • richardmitnick 1:55 pm on May 18, 2017 Permalink | Reply
    Tags: , Light,   

    From Princeton: “Bright future: Unlocking the potential of light” 

    Princeton University
    Princeton University

    Jan. 9, 2017 [Nothing like being prompt.]
    Bennett McIntosh for the Office of the Dean for Research

    One hundred years ago, Italian chemist Giacomo Ciamician predicted a future society that would run on sunlight.

    1
    Late at night in Princeton’s Frick Chemistry Laboratory, blue LED lights work overtime to catalyze new chemical reactions. The method, developed largely at Princeton, involves using light and a catalyst to join molecules that normally would not react with each other. The technique is already being used in industry to create medicines, solvents, plastics and other products. Shown above is Megan Shaw, a postdoctoral research associate in MacMillan’s group. Photo by Sameer A. Khan/Fotobuddy

    In a paper presented in 1912 to an international meeting of chemists in New York City, he foresaw a future of vibrant desert communities under “a forest of glass tubes and greenhouses of all sizes” where light-driven chemical reactions would produce not just energy but also wondrous medicines and materials.

    Ciamician’s vision has not yet arrived, but a handful of Princeton researchers have succeeded with one part of his legacy: they are harnessing light to perform previously impossible feats of chemistry. In Princeton’s Frick Chemistry Laboratory, blue LED lamps cast light on flask after flask of gently stirring chemicals that are reacting in ways they never have before to create tomorrow’s medicines, solvents, dyes and other industrial chemicals.

    The leader in this emerging field is David MacMillan, who arrived in Princeton’s chemistry department in 2006. He was intrigued by the potential for using light to coax new chemical reactions. Like most chemists, he’d spent years learning the rules that govern the interactions of elements such as carbon, oxygen and hydrogen, and then using those rules to fashion new molecules. Could light help change these rules and catalyze reactions that have resisted previous attempts at manipulation?

    Changing the rules

    The idea for using light as a catalyst had been explored since Ciamician’s time with limited success. Light can excite a molecule to kick loose one or more of its electrons, creating free radicals that are extremely reactive and readily form new bonds with one another. However, most chemists did not think this process could be controlled precisely enough to make a wide variety of precision molecules.

    But that changed in the summer of 2007.

    MacMillan and postdoctoral researcher David Nicewicz were working on a tough problem. The two scientists wanted to create chemical bonds between one group of atoms, called bromocarbonyls, and another group, known as aldehydes. “It was one of those longstanding challenges in the field,” MacMillan said. “It was one of those reactions that was really useful for making new medicines, but nobody knew how to do it.”

    Nicewicz had found a recipe that worked, but it involved using ultraviolet (UV) light. This high-energy form of light causes sunburn by damaging the molecules in the skin, and it also damaged the molecules in the reaction mixture, making the recipe Nicewicz had discovered less useful. MacMillan, who is Princeton’s James S. McDonnell Distinguished University Professor of Chemistry, asked Nicewicz to investigate how to do the transformation without UV light.

    Nicewicz recalled some experiments that he’d seen as a graduate student at the University of North Carolina-Chapel Hill. Researchers led by chemistry professor Malcolm Forbes had split water into oxygen and hydrogen fuel using visible light and a special molecule, a catalyst containing a metal called ruthenium. The approach was known as “photoredox catalysis” because particles of light, or photons, propel the exchange of electrons in a process called oxidation-reduction, or “redox” for short.

    Visible light is lower in energy than ultraviolet light, so Nicewicz and MacMillan reasoned that the approach might work without damaging the molecules. Indeed, when the researchers added a ruthenium catalyst to the reaction mixture and placed the flask under an ordinary household fluorescent lightbulb, the two scientists were astounded to see the reaction work almost perfectly the first time. “More times than not, the reaction you draw on the board never works,” Nicewicz said. Instead, the reaction produced astonishing amounts of linked molecules with high purity. “I knew right away it was a fantastic result,” he said.

    With support from the National Institutes of Health, MacMillan and Nicewicz spent the next year showing that the reaction was useful for many different types of bromocarbonyls and aldehydes, results that the team published in Science in October 2008. Research in the lab quickly expanded beyond this single reaction, and each new reaction hinted at a powerful shift in the rules of organic chemistry. “It just took off like gangbusters,” MacMillan said. “As time goes on you start to realize that there are nine or 10 different things that it can do that you didn’t think of.”

    Old catalysts, new tricks

    At the time that Nicewicz and MacMillan were making their discovery, chemistry professor Tehshik Yoon and his team at the University of Wisconsin-Madison found that combining the ruthenium catalyst with light produced a different chemical reaction. They published their work in 2008 in the Journal of the American Chemical Society the same day MacMillan’s paper appeared in Science. Within a year of MacMillan publishing his paper, Corey Stephenson, a University of Michigan chemistry professor, and his team found yet another photoredox-based reaction.

    With these demonstrations of the versatility of photoredox catalysts, other chemists quickly joined the search for new reactions. About 20 photoredox catalysts were already available for purchase from chemical catalogs due to previous research on water-splitting and energy storage, so researchers could skip the months-long process of building catalysts. However, by designing and tailoring new catalysts, the chemists unlocked the potential to use light to drive numerous new reactions, and today there are more than 400 photoredox catalysts available.

    The secret to these catalysts’ ability to drive specific reactions lies in their design. The catalysts consist of a central atom, often a metal atom such as ruthenium or iridium, surrounded by a halo of other atoms. Light frees an electron from the central atom, and the atoms surrounding the center act as a sort of channel that ushers the freed electrons toward the specific atoms that the chemists want to join.

    One scientist who became intrigued with the power of photoredox catalysts was Abigail Doyle, a Princeton associate professor of chemistry. Doyle, whose work is funded by the National Institutes of Health, uses nickel to help join two molecules. In 2014, she was searching for a way to conduct a reaction that had long eluded other scientists. She wanted to find a catalyst that could make perhaps the most common bond in organic chemistry — between carbon and hydrogen — reactive enough to couple to another molecule. Perhaps a photocatalyst could make a reactive free radical, allowing her to then bring in a nickel catalyst to attach the carbon-carbon bond.

    Unbeknownst to Doyle, the MacMillan lab had recently turned their attention to combining photoredox and nickel catalysts on a similar reaction, coupling molecules at the site of a carboxylate group, a common arrangement of atoms found in biological molecules from vinegar to proteins.

    Given the similarities in their findings, the MacMillan and Doyle labs decided to combine their respective expertise in nickel and photoredox chemistry. Together, the teams found a photocatalyst based on the metal iridium that worked with nickel to carry out both coupling reactions — at the carbon-hydrogen bond and at the carboxylate group. Their collaborative paper, published in Science July 25, 2014, showed the extent of photoredox catalysis’ power to couple molecules with these common features.

    The ability to combine molecules using natural features such as the carbon-hydrogen bond or the carboxylate group makes photoredox chemistry extremely useful. Often, chemists have to significantly modify a natural molecule to make it reactive enough to easily link to another molecule. One popular reaction — which earned a Nobel Prize in 2010 — requires several steps before two molecules can be linked. Skipping all these steps means a far easier and cheaper reaction — and one that is rapidly being applied.

    “It’s one of the fastest-adopted chemistries I’ve seen,” Doyle said. “A couple of months after we published, we were visiting pharmaceutical companies and many of them were using this chemistry.”

    The search for new drugs often involves testing vast libraries of molecules for ones that interact with a biological target, like trying thousands of keys to see which ones open a door. Pharmaceutical companies leapt at the chance to quickly and cheaply make many more kinds of molecules for their libraries.

    Merck & Co., Inc., a pharmaceutical company with research labs in the Princeton area, was one of the first companies to become interested in using the new approach — and in funding MacMillan’s research. The company donated $5 million to start Princeton’s Merck Center for Catalysis in 2006, and recently announced another $5 million in continued research funding.

    In addition to aiding drug discovery, photoredox-catalyzed reactions can produce new or less-expensive fine chemicals for flavorings, perfumes and pesticides, as well as plastic-like polymer materials. And the techniques keep getting cheaper. MacMillan published a paper June 23, 2016, in Science, showing that with the aid of a photoredox catalyst, a widely used reaction to make carbon-nitrogen bonds can be carried out with nickel instead of palladium. Because nickel is thousands of times cheaper than palladium, companies hoping to use the reaction were contacting MacMillan before the paper was even published.

    Spreading the light

    Doyle has continued to explore photoredox chemistry, as have other Princeton faculty members, including two new assistant professors, Robert Knowles and Todd Hyster.

    Hyster combines photoredox catalysis with reactions inspired by biology. Drugs often function by fitting in a protein like a hand fits in a glove. But just as placing a left hand in a right glove results in a poor fit, inserting a left-handed molecule into a protein designed for a right-handed molecule will give poor results. Many catalysts produce both the intended product and its mirror image, but by combining photoredox catalysts with artificial proteins, Hyster is finding reactions that can make that distinction.

    Hyster, who arrived at Princeton in summer 2015, was drawn to Princeton’s chemistry department in part because of the opportunities to share knowledge and experience with other groups researching photoredox catalysis. “The department is quite collegial, so there’s no barrier when talking to colleagues about projects that are broadly similar,” he said.

    Students from different labs chat about their work over lunch, teaching and learning informally — and formally, as the labs encourage collaboration and sharing expertise, said Emily Corcoran, a postdoctoral researcher who works with MacMillan. When Corcoran was trying to determine exactly how one of her reactions worked, she was able to consult with students in Knowles’ lab who had experience using sensitive magnetic measurements to find free radicals in the reaction mixture.

    “If you have a question, you can just walk down the hall and ask,” Corcoran said. “That really pushes all the labs forward at a faster pace.”

    A bright future

    After the graduate students go home at night, the blue LEDs continue to drive new chemical reactions and new discoveries. “This is really just the beginning,” Doyle said.

    Hyster thinks that within a few years, manufacturers may take advantage of photoredox chemistry to produce biological chemicals — such as insulin and the malaria drug artemisinin — to meet human needs. For his part, MacMillan envisions zero-waste chemical plants in the Nevada desert, driven not by fossil fuels but by the sun.

    MacMillan’s vision echoes that of the original photochemist, Ciamician. The Italian’s optimistic vision of a sunlit future is brighter than ever.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 9:05 pm on May 1, 2017 Permalink | Reply
    Tags: , Dimuon result, DZero, , heavy light and asymmetry, Light, Quantization - the particle that carries the electromagnetic force, Tevatron, Vector boson   

    From FNAL: “Light, heavy light and asymmetry” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    May 1, 2017
    Leo Bellantoni

    1
    Comparison of the forward backward asymmetry in Z → μ+ μ– for data (blue) and the best fit (red). The horizontal axis is the reconstructed mass of the muon pair; it is calculated from the energy and directions of the μ+ and μ–. DZero

    One of the major steps forward in particle physics was the development by Feynman, Tomonaga, Schwinger, Dyson and others of a theory of quantized electromagnetic forces in the late 1940s. The result of quantization, the particle that carries the electromagnetic force, is the photon, and it is an example — the first example, historically — of the type of particle that we call a vector boson. We use the symbol γ (gamma) for this particle.

    The weak nuclear force was discovered in the form of beta decay back in 1899 by Ernest Rutherford. Over the years, we came to realize that, like electromagnetic fields, these weak fields also have vector boson particles. Unlike electromagnetic forces, there are three different vector bosons for the weak force: One (the W+) has a positive charge, one (the W–) has a negative charge, and the third one, the Z boson, is uncharged. The weak vector bosons are also fairly heavy: They weigh about as much as an atom of krypton.

    Another difference between the electromagnetic boson and the weak force bosons is that, in many ways, the processes involving the weak force are asymmetric. For example, neutrinos, which respond only to the weak force, are for all practical purposes spinning in only one direction. It is sort of like how nearly every screw thread that you will see is right-handed.

    As you might have read in the May 1, 2014, DZero result, the γ and the Z are “actually formed from some blend of the more fundamental electroweak bosons, denoted b0 and w0.” Because of this blending, the Z is sometimes called a particle of heavy light. The amount of blending, or mixing as it is more usually called, is given by a number called the Weinberg angle or the weak mixing angle; the symbol is usually θW. Like the charge of the electron and the mass of Higgs boson, it is one of those fundamental constants that cannot be predicted and so must be measured.

    There are several ways of measuring the angle θW, and all rely on measuring processes involving the Z. In particular, the decays of a Z into positive and negative muons involve two competing effects (an “interference”) from the b0 and w0, which cause negative muons to be more forward than positive muons. “Forward” means having a tendency to be more aligned with the incoming proton direction than that of the incoming antiproton. These different rates thus cause a forward-backward directional asymmetry denoted AFB. The figure shows AFB plotted vs. a certain quantity, the “reconstructed mass” of the two muons. The interference creates an asymmetry at all masses, but near the mass of the Z boson (91 GeV), the asymmetry depends on the weak mixing angle.

    DZero has used this asymmetry in these dimuon events to measure the weak mixing angle. We find the square of the sine of that angle, sin2θW = 0.23002 ±0.00066. Previous sin2θW measurements at Stanford and at CERN had a puzzling discrepancy. Now, with this new dimuon result joining the previous DZero measurement with electrons and the CDF muon and electron results, the Tevatron will achieve a precision rivaling that of CERN and Stanford and gain the power to resolve this decades-old puzzle.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    FNAL Icon
    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 2:04 pm on December 3, 2016 Permalink | Reply
    Tags: , Light,   

    From Princeton: “Bright future: Princeton researchers unlock the potential of light to perform previously impossible feats” 

    Princeton University
    Princeton University

    November 11, 2016 [Just found this in social media.]
    Bennett McIntosh

    1
    No image caption. No image credit.

    One hundred years ago, Italian chemist Giacomo Ciamician predicted a future society that would run on sunlight.

    In a paper presented in 1912 to an international meeting of chemists in New York City, he foresaw a future of vibrant desert communities under “a forest of glass tubes and greenhouses of all sizes” where light-driven chemical reactions would produce not just energy but also wondrous medicines and materials.

    Ciamician’s vision has not yet arrived, but a handful of Princeton researchers have succeeded with one part of his legacy: they are harnessing light to perform previously impossible feats of chemistry. In Princeton’s Frick Chemistry Laboratory, blue LED lamps cast light on flask after flask of gently stirring chemicals that are reacting in ways they never have before to create tomorrow’s medicines, solvents, dyes and other industrial chemicals.

    The leader in this emerging field is David MacMillan, who arrived in Princeton’s chemistry department in 2006. He was intrigued by the potential for using light to coax new chemical reactions. Like most chemists, he’d spent years learning the rules that govern the interactions of elements such as carbon, oxygen and hydrogen, and then using those rules to fashion new molecules. Could light help change these rules and catalyze reactions that have resisted previous attempts at manipulation?

    Changing the rules

    The idea for using light as a catalyst had been explored since Ciamician’s time with limited success. Light can excite a molecule to kick loose one or more of its electrons, creating free radicals that are extremely reactive and readily form new bonds with one another. However, most chemists did not think this process could be controlled precisely enough to make a wide variety of precision molecules.

    But that changed in the summer of 2007.

    MacMillan and postdoctoral researcher David Nicewicz were working on a tough problem. The two scientists wanted to create chemical bonds between one group of atoms, called bromocarbonyls, and another group, known as aldehydes. “It was one of those longstanding challenges in the field,” MacMillan said. “It was one of those reactions that was really useful for making new medicines, but nobody knew how to do it.”

    Nicewicz had found a recipe that worked, but it involved using ultraviolet (UV) light. This high-energy form of light causes sunburn by damaging the molecules in the skin, and it also damaged the molecules in the reaction mixture, making the recipe Nicewicz had discovered less useful. MacMillan, who is Princeton’s James S. McDonnell Distinguished University Professor of Chemistry, asked Nicewicz to investigate how to do the transformation without UV light.

    Nicewicz recalled some experiments that he’d seen as a graduate student at the University of North Carolina-Chapel Hill. Researchers led by chemistry professor Malcom Forbes had split water into oxygen and hydrogen fuel using visible light and a special molecule, a catalyst containing a metal called ruthenium. The approach was known as “photoredox catalysis” because particles of light, or photons, propel the exchange of electrons in a process called oxidation-reduction, or “redox” for short.

    2
    David MacMillan is a leader in developing the use of light to catalyze chemical reactions — a technique called photoredox catalysis. (Photo by Sameer A. Khan/Fotobuddy)

    Visible light is lower in energy than ultraviolet light, so Nicewicz and MacMillan reasoned that the approach might work without damaging the molecules. Indeed, when the researchers added a ruthenium catalyst to the reaction mixture and placed the flask under an ordinary household fluorescent lightbulb, the two scientists were astounded to see the reaction work almost perfectly the first time. “More times than not, the reaction you draw on the board never works,” Nicewicz said. Instead, the reaction produced astonishing amounts of linked molecules with high purity. “I knew right away it was a fantastic result,” he said.

    With support from the National Institutes of Health, MacMillan and Nicewicz spent the next year showing that the reaction was useful for many different types of bromocarbonyls and aldehydes, results that the team published in Science in October 2008. Research in the lab quickly expanded beyond this single reaction, and each new reaction hinted at a powerful shift in the rules of organic chemistry. “It just took off like gangbusters,” MacMillan said. “As time goes on you start to realize that there are nine or 10 different things that it can do that you didn’t think of.”

    Old catalysts, new tricks

    At the time that Nicewicz and MacMillan were making their discovery, chemistry professor Tehshik Yoon and his team at the University of Wisconsin-Madison found that combining the ruthenium catalyst with light produced a different chemical reaction. They published their work in 2008 in the Journal of the American Chemical Society the same day MacMillan’s paper appeared in Science. Within a year of MacMillan publishing his paper, Corey Stephenson, a University of Michigan chemistry professor, and his team found yet another photoredox-based reaction.

    With these demonstrations of the versatility of photoredox catalysts, other chemists quickly joined the search for new reactions. About 20 photoredox catalysts were already available for purchase from chemical catalogs due to previous research on watersplitting and energy storage, so researchers could skip the months-long process of building catalysts. However, by designing and tailoring new catalysts, the chemists unlocked the potential to use light to drive numerous new reactions, and today there are more than 400 photoredox catalysts available.

    The secret to these catalysts’ ability to drive specific reactions lies in their design. The catalysts consist of a central atom, often a metal atom such as ruthenium or iridium, surrounded by a halo of other atoms. Light frees an electron from the central atom, and the atoms surrounding the center act as a sort of channel that ushers the freed electrons toward the specific atoms that the chemists want to join.

    One scientist who became intrigued with the power of photoredox catalysts was Abigail Doyle, a Princeton associate professor of chemistry. Doyle, whose work is funded by the National Institutes of Health, uses nickel to help join two molecules. In 2014, she was searching for a way to conduct a reaction that had long eluded other scientists. She wanted to find a catalyst that could make perhaps the most common bond in organic chemistry — between carbon and hydrogen — reactive enough to couple to another molecule. Perhaps a photocatalyst could make a reactive free radical, allowing her to then bring in a nickel catalyst to attach the carbon-carbon bond.

    Unbeknownst to Doyle, the MacMillan lab had recently turned their attention to combining photoredox and nickel catalysts on a similar reaction, coupling molecules at the site of a carboxylate group, a common arrangement of atoms found in biological molecules from vinegar to proteins.

    Given the similarities in their findings, the MacMillan and Doyle labs decided to combine their respective expertise in nickel and photoredox chemistry. Together, the teams found a photocatalyst based on the metal iridium that worked with nickel to carry out both coupling reactions — at the carbon-hydrogen bond and at the carboxylate group. Their collaborative paper, published in Science July 25, 2014, showed the extent of photoredox catalysis’ power to couple molecules with these common features.

    The ability to combine molecules using natural features such as the carbon-hydrogen bond or the carboxylate group makes photoredox chemistry extremely useful. Often, chemists have to significantly modify a natural molecule to make it reactive enough to easily link to another molecule. One popular reaction — which earned a Nobel Prize in 2010 — requires several steps before two molecules can be linked. Skipping all these steps means a far easier and cheaper reaction — and one that is rapidly being applied.

    “It’s one of the fastest-adopted chemistries I’ve seen,” Doyle said. “A couple of months after we published, we were visiting pharmaceutical companies and many of them were using this chemistry.”

    The search for new drugs often involves testing vast libraries of molecules for ones that interact with a biological target, like trying thousands of keys to see which ones open a door. Pharmaceutical companies leapt at the chance to quickly and cheaply make many more kinds of molecules for their libraries.

    Merck & Co., Inc., a pharmaceutical company with research labs in the Princeton area, was one of the first companies to become interested in using the new approach — and in funding MacMillan’s research.The company donated $5 million to start Princeton’s Merck Center for Catalysis in 2006, and recently announced another $5 million in continued research funding.

    In addition to aiding drug discovery, photoredoxcatalyzed reactions can produce new or less expensive fine chemicals for flavorings, perfumes and pesticides, as well as plastic-like polymer materials. And the techniques keep getting cheaper. MacMillan published a paper June 23, 2016, in Science showing that with the aid of a photoredox catalyst, a widely used reaction to make carbon-nitrogen bonds can be carried out with nickel instead of palladium. Because nickel is thousands of times cheaper than palladium, companies hoping to use the reaction were contacting MacMillan before the paper was even published.

    Spreading the light

    Doyle has continued to explore photoredox chemistry, as have other Princeton faculty members, including two new assistant professors, Robert Knowles and Todd Hyster.

    Hyster combines photoredox catalysis with reactions inspired by biology. Drugs often function by fitting in a protein like a hand fits in a glove. But just as placing a left hand in a right glove results in a poor fit, inserting a left-handed molecule into a protein designed for a right-handed molecule will give poor results. Many catalysts produce both the intended product and its mirror image, but by combining photoredox catalysts with artificial proteins, Hyster is finding reactions that can make that distinction.

    Hyster, who arrived at Princeton in summer 2015, was drawn to Princeton’s chemistry department in part because of the opportunities to share knowledge and experience with other groups researching photoredox catalysis. “The department is quite collegial, so there’s no barrier when talking to colleagues about projects that are broadly similar,” he said.

    Students from different labs chat about their work over lunch, teaching and learning informally — and formally, as the labs encourage collaboration and sharing expertise, said Emily Corcoran, a postdoctoral researcher who works with MacMillan. When Corcoran was trying to determine exactly how one of her reactions worked, she was able to consult with students in Knowles’ lab who had experience using sensitive magnetic measurements to find free radicals in the reaction mixture.

    “If you have a question, you can just walk down the hall and ask,” Corcoran said. “That really pushes all the labs forward at a faster pace.”

    A bright future

    After the graduate students go home at night, the blue LEDs continue to drive new chemical reactions and new discoveries. “This is really just the beginning,” Doyle said.

    Hyster thinks that within a few years, manufacturers may take advantage of photoredox chemistry to produce biological chemicals — such as insulin and the malaria drug artemisinin — to meet human needs. For his part, MacMillan envisions zero-waste chemical plants in the Nevada desert, driven not by fossil fuels but by the sun.

    MacMillan’s vision echoes that of the original photochemist, Ciamician. The Italian’s optimistic vision of a sunlit future is brighter than ever.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 11:20 am on June 16, 2016 Permalink | Reply
    Tags: Circularly polarized light, Delta undulator, Light,   

    From SLAC: “With Spiraling Light, SLAC X-ray Laser Offers New Glimpses of Molecules” 


    SLAC Lab

    June 15, 2016

    1
    The side-to-side motion of electrons in a beam can be circular, elliptical, or linear, depending on the position of the Delta undulator’s magnet rows. These different motions then create circular, elliptical, or linear polarization in the light pulse. (SLAC National Accelerator Laboratory)

    A new device at the Department of Energy’s SLAC National Accelerator Laboratory allows researchers to explore the properties and dynamics of molecules with circularly polarized, or spiraling, light.

    The use of polarized light is important in the study of many molecules and processes that affect our everyday lives. It can be used to tell the difference between chiral molecules that have “left-handed” and “right-handed” variations, which affects everything from your sense of smell and taste – such as the difference between oranges and lemons, or spearmint and caraway seeds – to life-altering drugs such as thalidomide, in which one version helps ease nausea, but the other can cause abnormal limb growth in unborn children.

    2

    The new Delta undulator produces spiraling X-ray light. (SLAC National Accelerator Laboratory)

    3
    SLAC staff assemble the Delta undulator. (SLAC National Accelerator Laboratory)

    With the new Delta undulator, the Linac Coherent Light Source (LCLS) X-ray laser can now be tailored to look at changes in magnetic materials happening faster than a trillionth of a second, as well as fleeting processes that involve chiral compounds central to areas of biological and chemical research. LCLS is a DOE Office of Science User Facility.

    SLAC/LCLS
    SLAC/LCLS

    “We have already used these X-rays in a couple of studies, and the researchers seemed quite happy with the result,” said James MacArthur, a physics graduate student at Stanford University and part of the SLAC team that built the Delta undulator.

    How Spiraling Light Is Made

    LCLS generates extremely short, bright pulses of X-ray laser light by sending an electron beam through what’s called an undulator. The undulator contains pairs of magnets that force the electrons to wiggle. This motion gives off energy in the form of X-rays, which interact with the electron beam to form laser pulses that can be used for experiments.

    Before the addition of the Delta, the light delivered to experimental stations was always linearly polarized. Polarization refers to the way a light wave vibrates as it travels forward, and linearly polarized light is restricted to one direction. But circularly polarized light vibrates in two directions, producing a pattern like a corkscrew.

    With the Delta, four rows of strong magnets shift to polarize X-rays in a linear, elliptical, or circular fashion.

    3
    5
    Above: Electrons wiggle between two rows of magnets in a traditional undulator, creating X-rays. These X-rays, or light waves, are linearly polarized. Below: With four moving rows of magnets, the Delta undulator can create circularly polarized, or spiraling, light. (SLAC National Accelerator Laboratory)

    Scientists can use the spiraling light to reveal the orientation of molecules in certain materials, and even provide subatomic details as fine as electron distribution and spin.

    Over the past few decades, the ability to control the polarization of light has led to many breakthroughs using optical lasers. Researchers in Italy recently extended this ability into the extreme ultraviolet regime, using the FERMI Free Electron Laser. The beam at LCLS now opens doors to experiments using X-rays, which are able to probe matter in wholly new ways.

    Studies With Spiraling Light

    There are several types of experiments made possible by circularly polarized light. People who study magnetic storage for computing, for example, use spiraling light to watch magnetization changes to develop new methods and materials for faster and more compact storage devices.

    Now, with the power of the world’s strongest X-ray laser, the spiraling light can be delivered in extremely short and intense pulses over a wide range of energies.

    “We can now study the dynamics of ultrafast magnetization in a more substantive and specific way than was previously possible,” said Daniel Higley, an applied physics graduate student at Stanford. Higley is part of the Stanford Institute for Materials and Energy Sciences (SIMES), a joint institute between Stanford and SLAC.

    “One of the key things about using X-rays is that they’re quite specific, tuned to distinct energies. So we can study, in this case, what the magnetization dynamics are for individual chemical elements,” Higley said. “And the short pulses produced by an X-ray laser allow you to take a snapshot of things that happen very fast.”

    The researchers can also gather the needed data quickly. The spiraling light produced by the Delta is nearly 100 percent polarized and orders of magnitude brighter than light produced by any other type of X-ray source with such short pulses. This enables measurement of ultrafast magnetism with unprecedented accuracy and speed. The team described such measurements in a recent Review of Scientific Instruments paper.

    Scientists can also use spiraling light to probe chiral molecules, those with “right-handed” or “left-handed” structures. These subtle differences in arrangement are key to understanding the function of many substances in biological and chemical research, including certain amino acids and sugars, pharmaceuticals and pesticides.

    This light can be used to study how X-rays trigger precise, fleeting changes in chiral molecules like amino acids, and researchers can create snapshots of how radiation damages the molecular building blocks of our bodies.
    Building the Delta

    The first Delta undulator was built at Cornell nearly a decade ago. For the LCLS version, the SLAC team, led by Heinz-Dieter Nuhn, wanted to build a much bigger version of the Cornell prototype.

    But they could not copy the original exactly; it needed adjustments to work at LCLS.

    “We started with some ideas, and found they weren’t as good as we thought,” said Alberto Lutman, head of SLAC’s Delta operations team. “It took us about a year to refine the design and work out the kinks during commissioning. But as a result of all that effort, it’s gotten better and better.”

    Bringing the device up to working condition also required a large collaboration. A Cornell scientist who designed and built the first Delta undulator, Alexander Temnykh, gave input on the blueprint and initial tests. Colleagues at Germany’s DESY and the European X-ray Free-Electron Laser helped provide the measurements needed to calibrate the new equipment.

    One of the design challenges related to size. Researchers at LCLS typically use 30 to 50 meters of undulators to produce a high-quality X-ray beam.

    “The Delta undulator is only 3.2 meters long,” MacArthur said. “So we had to come up with a way to produce a lot of radiation and create a high degree of circular polarization from a short undulator.”

    In a Nature Photonics paper published in May, the Delta team reported that the undulator can produce high-intensity light at nearly 100 percent polarization.

    “It wasn’t known how well the undulator would work as we were developing it,” Lutman said. “It works, and it works nicely.”

    What’s Next for the Delta

    Research and development is underway for multiple Delta-II undulators that will produce spiraling light compatible with the beam of LCLS-II, the next generation of LCLS. LCLS-II will be 10,000 times brighter, on average, than LCLS, enabling high precision studies of even finer aspects of ultrafast magnetism and chirality.

    SLAC/LCLS-II line
    SLAC/LCLS-II line

    The Delta team will develop even more ways to manipulate polarized light. One scheme involves delivering X-rays of different energies and polarizations in a single experiment.

    “The entire Delta team has worked hard to develop a way we can produce circularly polarized light that’s custom-made for research needs,” said Mike Dunne, LCLS director. “We’re excited to be able to offer this new capability to the scientific community.”

    Citations: Lutman et al., Nature Photonics, 09 May 2016 (10.1038/nphoton.2016.79); Higley et al., Review of Scientific Instruments, 22 March 2016 (10.1063/1.4944410).

    See the full article here .

    Please help promote STEM in your local schools.

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 12:07 pm on May 17, 2016 Permalink | Reply
    Tags: , , Light   

    From GIZMODO: “Scientists Discover Light That Travels Unlike Any Other” 

    GIZMODO bloc

    GIZMODO

    5.17.16
    Jamie Condliffe

    1
    Image by Reha Mark/Shutterstock
    _________________________________________________

    Not all light is made equal. Now, a team of physicists has discovered that photons can travel differently to any other light that scientists have seen in the past.

    The team from Trinity College Dublin has been studying the angular momentum of light. As a beam of light travels through space, it propagates forward in a straight line but it can be rotating about the axis along which it travels, like a corkscrew twirling through space. Until now, the angular momentum resulting from that rotation was always thought to be an integer multiple of Planck’s constant.

    But new experiments by the team show that it’s possible for photons to have angular momentum that is half of those values. The team initially predicted the phenomenon using theoretical models, then tested it using specially constructed experimental kit that could twist a light beam by passing it through crystals of material. Ultimately, they found that half-multiples of angular velocity were in fact possible. The research is published* in Science Advances.

    It’s a subtle but interesting finding, though one whose immediate impacts are hard to predict. “What I think is so exciting about this result is that even this fundamental property of light, that physicists have always thought was fixed, can be changed,” explained Assistant Professor Paul Eastham, one of the researchers, in a press release. The team does, however, reckon it could find application in light-based communications, to better encode and secure data in light beams

    Science paper:
    There are many ways to spin a photon: Half-quantization of a total optical angular momentum

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “We come from the future.”

    GIZMOGO pictorial

     
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