Hexbyte Glen Cove Fiber lasers poised to advance lab’s development of practical laser-plasma accelerators

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Berkeley Lab scientist Tong Zhou conducting fiber laser combination experiments. An ongoing multi-institutional project to coherently combine the output of fast-pulsing but low-energy fiber lasers could be the secret to having both high energy and high repetition rate—key to the next steps in laser-plasma accelerators. Credit: Marilyn Sargent/Berkeley Lab

The next phase in the development of laser-plasma particle accelerators (LPAs)—potentially game-changing tools for research and practical applications—is underway at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). A new approach to high-power lasers—combining the pulses from many fast-acting but lower-energy optical fiber lasers—will energize these super-compact accelerators.

Berkeley Lab researchers have zeroed in on the limitations of LPA development efforts and believe they have found a new path forward with optical fiber lasers.

Cameron Geddes, director of Berkeley Lab’s Accelerator Technology and Applied Physics (ATAP) Division, said, “With all the recent technological breakthroughs in fiber lasers and accelerators, it’s time to bring them together—to develop a next generation of compact and precision-controllable accelerators that can be used in a wide range of applications.”

LPAs: Small is the new big

LPAs, in which the Berkeley Lab Laser Accelerator (BELLA) Center is among the leaders, are a radically compact approach to particle acceleration, notable for achieving particle energies in centimeters that would require tens of meters with conventional technologies.

Conventional accelerators use microwaves in resonant metallic cavities to impart high energies to beams of subatomic particles. This mature technology, which can take several circular or linear forms, makes accelerators powerful engines of scientific discovery, in addition to numerous practical applications in medicine, industrial processing, and national security. Many of them are, however, large and costly.

LPAs offer an alternative way to accelerate and boost the energies of the particles. Rather than using microwaves, an intense beam of laser light fired through a gas will generate a plasma wave that charged can ride like a surfer.

Radically smaller than present-day means of achieving the same beam energy, LPAs would be attractive in many applications, ranging from biomedical treatment to free-electron-lasers research centers to nuclear nonproliferation. Ultimately they might even be the basis for a new generation of colliders, orders of magnitude smaller than today’s, for high-energy .

LPAs have been successfully demonstrated (BELLA Center holds the record, having accelerated electrons to an energy of 7.8 billion electron-volts in just 20 cm), but they require high laser power. A laser like the BELLA Petawatt produces output comparable to the entire output of the world’s electrical grid for an extremely brief instant, focused into a pulse the diameter of a human hair. However, it can only muster a pulse every second or so. Useful applications will require high laser power delivered in much more frequent pulses. That’s where the new fiber laser project comes in.

Combining laser beams so that they truly resemble one powerful beam is challenging. The next steps being taken by the project that recently commenced, headed by Zhou, a scientist in Berkeley Lab’s ATAP Division, and supported in part by the Gordon and Betty Moore Foundation, will build upon existing work on spatial combining, as well as amplification in doped fibers. Spectral beam combining (the subject of Zhou’s prestigious Early Career Research Program award from the Department of Energy’s Office of High Energy Physics) and temporal stacking are other ongoing aspects of the overall effort to produce a high-power kilohertz beam from fiber lasers. Credit: Russell Wilcox, Tong Zhou, Almantas Galvanauskas, Cameron Geddes

Laser teamwork means powerful pulses

Fiber lasers (based on optical fibers that are like those familiar from telecommunications and computer networking, but designed for optimal laser emission) are fast, but small. Each optical fiber provides a channel no wider than a human hair, and can only emit so much power. The project now getting underway—building upon several years of groundwork at Berkeley Lab, the University of Michigan, and Lawrence Livermore National Laboratory—will further develop a scheme called “coherent beam combining.” The goal is pulses energetic enough to drive an LPA, but delivered a thousand times a second.

The new project is led by Berkeley Lab researcher Tong Zhou. Berkeley Lab team members working on fiber laser development also include Russell Wilcox, Qiang Du, Thorsten Stezelberger, and Jeroen van Tilborg. Almantas Galvanauskas and his students at the University of Michigan and Leily Kiani at Lawrence Livermore National Laboratory also play important roles in the program.

The overall effort, continuing to build upon several years of progress, involves spatial, temporal, and spectral combining in a way that preserves “coherence” (a distinctive quality of laser beams, necessary for LPAs). It aims to bundle the relatively low-powered pulses from many fibers into 30-50 femtosecond long, 200-millijoule pulses with peak power much greater than one terawatt. This would be the highest energy and peak power ever obtained from a fiber laser, and more than sufficient for demonstrations of laser-plasma acceleration.

“Their power consumption would be improved compared to conventional lasers, and their ability to dissipate heat is excellent, addressing other challenges in building high-power lasers,” Zhou said.

The long-term goal is a for high-energy physics. For those purposes, an LPA would need laser energy on the order of 10 joules in short pulses (30 to 100 femtoseconds each), with a repetition rate greater than 10,000 pulses per second—specifications far beyond existing laser technology. Fiber lasers are a promising candidate for solving this problem, and could in the meanwhile power the many spinoff applications of LPAs.

Power isn’t the only important thing in a system that has to deliver a hair-thin beam into a capillary with an inside diameter just a few times larger than that. Measurement and active feedback for precision control of such attributes as pointing angle and position are the subjects of complementary work at BELLA Center. Machine learning is emerging as an important control technique.

“We want to not only build a laser system that sets power and energy records, but also state-of-the-art controls, then use it to realize the first high-average-power, high-repetition-rate, laser-driven accelerator in the world,” Geddes said.

Such a system, coherently combining ultrashort from many fiber lasers at a kilohertz repetition rate, is a frontrunner for the laser technology of kBELLA, the proposed next generation of the Berkeley Lab Laser Accelerator (BELLA) Center’s LPA drivers.

Fiber lasers poised to advance lab’s development of practical laser-plasma accelerators (2021, December 6)
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Hexbyte Glen Cove 'Sex, lasers and male competition:' fruit flies win genetic race with rivals thumbnail

Hexbyte Glen Cove ‘Sex, lasers and male competition:’ fruit flies win genetic race with rivals

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UC researchers studied the sex combs of the fruit fly Drosophilia bipectinata. Credit: Michal Polak/UC

Scientists have accepted natural selection as a driver of evolution for more than 160 years, thanks to Charles Darwin.

But University of Cincinnati biologist Michal Polak says Darwin’s book “The Descent of Man” only tells part of the story. Sometimes when the victor vanquishes his sexual rival, the quest to pass genes to the next generation is just beginning.

According to a new UC study published in the journal Current Biology, male flies with the most impressive sexual ornamentation also have super sperm that can outcompete that of rivals in the post-mating fertilization game.

UC studied Drosophila bipectinata, a tiny red-eyed fruit fly from the South Pacific. The male’s forelegs have a distinctive “sex comb,” dark bristles that female fruit flies find appealing—like the colorful train of a male peacock. Scientists previously found that female flies prefer males with more robust sex combs, which the males use to grasp the female’s abdomen before mating.

UC researchers found a strong link between the most impressive sex combs and that male’s competitive success at passing on his genes even after a female fly has mated with other flies. And this competitive edge persisted even after the male’s sex comb was surgically removed with a high-precision laser in UC experiments.

“This is the first robust demonstration of a genetic link between a traditionally Darwinian trait and success in postcopulatory sexual competition,” Polak said. “That’s the surprising link: precopulatory and postcopulatory fitness.”

In his groundbreaking 1859 book “On the Origin of Species,” Darwin framed the idea of by describing how the “fittest” animals pass on their genes to the next generation. This fitness is manifested in having the largest antlers, the most vibrant colors or the vigor to defend a territory.

But Darwin’s theory was incomplete, Polak said, because it failed to recognize that sexual selection continues during and after mating. Female fruit flies are promiscuous, often choosing multiple mates. Fruit flies are hardly alone in that regard, Polak said.

“Promiscuity is much more common across animal species than once was thought,” Polak said.

UC biologist Michal Polak studies the competitive race to pass on genes that takes place after multiple males mate with a female. Credit: Andrew Higley/UC Creative

Scientists living in prim and proper Victorian England did not give enough consideration to the microscopic race to fertilize that begins after mating among multiple successful suitors.

“You have to consider the social context in which Darwin was living,” Polak said.

What females gain from mating with multiple suitors is not always clear, Polak said. But when they do, postcopulatory sexual selection provides a competitive edge.

“It’s evident even in primates. Female chimpanzees and bonobos are promiscuous, so the males have large testes that produce big volumes of sperm,” Polak said.

“And you have species like gorillas where females are not promiscuous. Silverback males enforce monogamy. And lo and be hold, their testes are much smaller relative to body size compared to chimps.”

And if you’re wondering, the relative size of human testes falls somewhere between gorillas and chimps, Polak said.

Polak, a professor of biology in UC’s College of Arts and Sciences, decided to study this species of fruit fly after encountering it while conducting fieldwork in Queensland, Australia.

“I was watching these flies mate on a fruit and looked under the microscope and saw these beautiful sex combs. I thought it would make a good model system to study,” Polak said.

“Sexual selection picks up on these traits and they become really exaggerated,” he said.

UC researchers found a link between a fruit fly’s sexual ornamentation and its success over rivals in fertilizing eggs. Pictured are UC graduate Kassie Hooker, left, and UC biologists Joshua Benoit and Michal Polak. Credit: Andrew Higley/UC Creative

For their study, UC biologists artificially selected males with the largest and smallest sex combs in 11 successive generations of fruit flies to create high and low genetic lines.

Kassie Hooker from 2012 to 2015 worked in Polak’s lab as an undergraduate biology student, undertaking the arduous task of categorizing generations of male fruit flies based on the size of the sex combs on their legs. By counting the teeth in each comb, she separated the males with the largest and smallest sex combs to create distinct genetic lines.

To show that the male fruit fly’s sex comb doesn’t provide any reproductive benefit in mating, researchers used ultraprecise lasers to trim the sex in the high line males to mimic those found in the low line males. But these postsurgical males continued to fertilize more eggs even when females mated with lower-line males first.

The research was supported by the National Science Foundation.

UC assistant professor Joshua Benoit, a study co-author, analyzed the RNA of the flies and identified seminal fluid genes that may be responsible for giving high-line a fertilization advantage.

“There aren’t many studies more interesting than this one,” Benoit said. “Sex, lasers, and male competition, which could describe most 1980s action movies.”

Darwin proposed the theory of sexual selection to account for the evolution of male weaponry and extravagant ornamental displays, Polak said. But UC’s study found a far more complex and interesting battle among the sexes.

“We established a link between Darwinian traits and the postcopulatory arena, which Darwin didn’t recognize was important in evolution at all,” Polak said.

More information:
Michal Polak et al, Positive genetic covariance between male sexual ornamentation and fertilizing capacity, Current Biology (2021). DOI: 10.1016/j.cub.2021.01.046

‘Sex, lasers and male competition:’ fruit flies win genetic race with rivals (2021, February 12)
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Hexbyte Glen Cove Lasers and molecular tethers create perfectly patterned platforms for tissue engineering thumbnail

Hexbyte Glen Cove Lasers and molecular tethers create perfectly patterned platforms for tissue engineering

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Top view of two collagen hydrogels that researchers decorated with immobilized mCherry proteins, which glow red under fluorescent light. The team scanned near-infrared lasers in the shapes of a monster (left) and Seattle’s Space Needle (right) to create these patterns. Black regions were not scanned with the laser, and so the mCherry protein did not adhere to those portions of the hydrogel. Scale bar is 50 micrometers. Credit: Batalov et al., PNAS, 2021

Imagine going to a surgeon to have a diseased or injured organ switched out for a fully functional, laboratory-grown replacement. This remains science fiction and not reality because researchers today struggle to organize cells into the complex 3-D arrangements that our bodies can master on their own.

There are two major hurdles to overcome on the road to laboratory-grown organs and tissues. The first is to use a biologically compatible 3-D in which cells can grow. The second is to decorate that scaffold with biochemical messages in the correct configuration to trigger the formation of the desired organ or tissue.

In a major step toward transforming this hope into reality, researchers at the University of Washington have developed a technique to modify naturally occurring biological polymers with protein-based biochemical messages that affect cell behavior. Their approach, published the week of Jan. 18 in the Proceedings of the National Academy of Sciences, uses a near-infrared laser to trigger chemical adhesion of protein messages to a scaffold made from biological polymers such as collagen, a connective tissue found throughout our bodies.

Mammalian cells responded as expected to the adhered protein signals within the 3-D scaffold, according to senior author Cole DeForest, a UW associate professor of chemical engineering and of bioengineering. The proteins on these biological scaffolds triggered changes to messaging pathways within the cells that affect cell growth, signaling and other behaviors.

These methods could form the basis of biologically based scaffolds that might one day make functional laboratory-grown tissues a reality, said DeForest, who is also a faculty member with the UW Molecular Engineering and Sciences Institute and the UW Institute for Stem Cell and Regenerative Medicine.

The team used near-infrared lasers to create this intricate pattern in the shape of a human heart of immobilized mCherry proteins, which glow red under fluorescent light, within a collagen hydrogel. On the left is a composite image of 3D slices from the gel. On the right are cross-sectional views of the mCherry patterns. Scale bar is 50 micrometers. Credit: Batalov et al., PNAS, 2021

“This approach provides us with the opportunities we’ve been waiting for to exert greater control over cell function and fate in naturally derived biomaterials—not just in three-dimensional space but also over time,” said DeForest. “Moreover, it makes use of exceptionally precise photochemistries that can be controlled in 4-D while uniquely preserving and bioactivity.”

DeForest’s colleagues on this project are lead author Ivan Batalov, a former UW postdoctoral researcher in chemical engineering and bioengineering, and co-author Kelly Stevens, a UW assistant professor of bioengineering and of laboratory medicine and pathology.

Their method is a first for the field, spatially controlling cell function inside naturally occurring biological materials as opposed to those that are synthetically derived. Several research groups, including DeForest’s, have developed light-based methods to modify synthetic scaffolds with protein signals. But natural biological polymers can be a more attractive scaffold for tissue engineering because they innately possess biochemical characteristics that cells rely on for structure, communication and other purposes.

“A natural biomaterial like collagen inherently includes many of the same signaling cues as those found in native tissue,” said DeForest. “In many cases, these types of materials keep cells ‘happier’ by providing them with similar signals to those they would encounter in the body.”

They worked with two types of biological polymers: collagen and fibrin, a protein involved in blood clotting. They assembled each into fluid-filled scaffolds known as hydrogels.

A top view of a cylindrical fibrin hydrogel. By design, the right side of the hydrogel contains immobilized Delta-1 proteins, which activate Notch signaling pathways within cells. The left side does not contain immobilized Delta-1 (see insert). The team introduced human bone cancer cells, which were engineered to glow when their Notch signaling pathways are activated, into the hydrogel. The right side of the hydrogel glows brightly, indicating that cells in that region have activated their Notch signaling pathways. Cells on the left side of the hydrogel have not. Scale bar is 1 millimeter. Credit: Batalov et al., PNAS, 2021

The signals that the team added to the hydrogels are proteins, one of the main messengers for cells. Proteins come in many forms, all with their own unique chemical properties. As a result, the researchers designed their system to employ a universal mechanism to attach proteins to a hydrogel—the binding between two chemical groups, an alkoxyamine and an aldehyde. Prior to hydrogel assembly, they decorated the collagen or fibrin precursors with alkoxyamine groups, all physically blocked with a “cage” to prevent the alkoxyamines from reacting prematurely. The cage can be removed with ultraviolet light or a near-infrared laser.

Using methods previously developed in DeForest’s laboratory, the researchers also installed aldehyde groups to one end of the proteins they wanted to attach to the hydrogels. They then combined the aldehyde-bearing proteins with the alkoxyamine-coated hydrogels, and used a brief pulse of light to remove the cage covering the alkoxyamine. The exposed alkoxyamine readily reacted with the aldehyde group on the proteins, tethering them within the hydrogel. The team used masks with patterns cut into them, as well as changes to the laser scan geometries, to create intricate patterns of protein arrangements in the hydrogel—including an old UW logo, Seattle’s Space Needle, a monster and the 3-D layout of the human heart.

The tethered proteins were fully functional, delivering desired signals to cells. Rat liver cells—when loaded onto collagen hydrogels bearing a protein called EGF, which promotes cell growth—showed signs of DNA replication and cell division. In a separate experiment, the researchers decorated a fibrin hydrogel with patterns of a protein called Delta-1, which activates a specific pathway in cells called Notch signaling. When they introduced human bone cancer cells into the hydrogel, cells in the Delta-1-patterned regions activated Notch signaling, while in areas without Delta-1 did not.

These experiments with multiple biological scaffolds and protein signals indicate that their approach could work for almost any type of protein signal and biomaterial system, DeForest said.

“Now we can start to create scaffolds with many different signals, utilizing our understanding of cell signaling in response to specific combinations to modulate critical biological function in time and space,” he added.

With more-complex signals loaded on to hydrogels, scientists could then try to control stem cell differentiation, a key step in turning into science fact.

More information:
Ivan Batalov el al., “Photopatterned biomolecule immobilization to guide three-dimensional cell fate in natural protein-based hydrogels,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.2014194118

Lasers and molecular tethers create perfectly patterned platforms for tissue engineering (2021, January 18)
retrieved 19 January 2021
from https://phys.org/news/2021-01-lasers-molecular-tethers-perfectly-patterned.html

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