Jamie Raskin to Give Milchberg Lecture on March 28

Congressman Jamie Raskin of Maryland’s 8th Congressional District will give the fourth Irving and Renee Milchberg Endowed Lecture on Thursday, March 28 at 1 p.m. in the lecture hall (1412) of the John S. Toll Physics Building. Rep. Raskin will discuss Democracy, Autocracy and the Threat to Reason in the 21st Century.

University of Maryland Professor of Physics and Electrical and Computer Engineering Howard Milchberg, his wife Rena, and their three children Moses, Mollie, and Max, established the lecture in memory of Howard's late parents, Renee and Irving Milchberg. Renee and Irving were witnesses to and victims of what can happen to society when ideology and lies are accepted in lieu of facts.

The talk is free and open to the public. Please register: https://science.umd.edu/events/milchberg-2024.html

Rep. Raskin is serving his fourth term representing the eighth district, which includes most of Montgomery County and a small part of Prince George's County.  He is the Ranking Member of the House Committee on Oversight and Accountability in the 118th Congress. 

Rep. Jamie RaskinRep. Jamie Raskin

Previously Rep. Raskin served three terms on the House Judiciary Committee and the Committee on House Administration. He served two terms on the Rules Committee and the Coronavirus Select Subcommittee. During the 117th Congress he served as Chair of the Oversight Subcommittee on Civil Rights and Civil Liberties and Chair of the Rules Subcommittee on Expedited Procedure. Rep. Raskin was the lead impeachment manager in the second impeachment trial of former president Donald Trump and served on the Select Committee to Investigate the January 6th Attack on the United States Capitol.

Prior to his time in Congress, Raskin was a three-term State Senator in Maryland, where he also served as the Senate Majority Whip. Congressman Raskin is a graduate of Harvard College and Harvard Law School and is a former editor of the Harvard Law Review. He is the author of Unthinkable: Trauma, Truth, and the Trials of American Democracy.

 Irving and Renee Milchberg Endowed Lecture Speakers:

2024:  Congressman Jamie Raskin, "Democracy, Autocracy and the Threat to Reason in the 21st Century"
2023: Jonathan Moreno, University of Pennsylvania, "Bioethics and the Rules-Based International Order"  
2021: James Glanz, reporter for the New York Times, "The Public Relations Machine in Science: A Self-Inflicted Wound?"
2019: Susan Eisenhower, President and CEO of the Eisenhower Institute, "Lessons from 1945: Ethics, the War in Europe, and its Enduring Legacy"

New Laser Experiment Spins Light Like a Merry-go-round

In day-to-day life, light seems intangible. We walk through it and create and extinguish it with the flip of a switch. But, like matter, light actually carries a little punch—it has momentum. Light constantly nudges things and can even be used to push spacecraft. Light can also spin objects if it carries orbital angular momentum (OAM)—the property associated with a rotating object’s tendency to keep spinning.

Scientists have known that light can have OAM since the early 90s, and they’ve discovered that the OAM of light is associated with swirls or vortices in the light’s phase—the position of the peaks or troughs of the electromagnetic waves that make up the light. Initially, research on OAM focused on vortices that exist in the cross section of a light beam—the phase turning like the propeller of a plane flying along the light’s path. But in recent years, physicists at UMD, led by UMD Physics Professor Howard Milchberg, have discovered that light can carry its OAM in a vortex turned to the side—the phase spins like a wheel on a car, rolling along with the light. The researchers called these light structures spatio-temporal optical vortices (STOVs) and described the momentum they carry as transverse OAM.

“Before our experiments, it wasn’t appreciated that particles of light—photons—could have sideways-pointing OAM,” Milchberg says. “Colleagues initially thought it was weird or wrong. Now research on STOVs is rapidly growing worldwide, with possible applications in areas such as optical communications, nonlinear optics, and exotic forms of microscopy.”

In an article published on Feb. 28, 2024, in the journal Physical Review X, the team describes a novel technique they used to change the transverse OAM of a light pulse as it travels. Their method requires some laboratory tools, like specialized lasers, but in many ways, it resembles spinning a playground merry-go-round or twisting a wrench.Similarities exist between spinning everyday items, like a playground merry-go-round, and spinning vortices of light. Image credit: Martin VorelSimilarities exist between spinning everyday items, like a playground merry-go-round, and spinning vortices of light. Image credit: Martin Vorel

“Because STOVs are a new field, our main goal is gaining a fundamental understanding of how they work. And one of the best ways to do that is to mess with them,” says Scott Hancock, a UMD physics postdoctoral researcher and first author of the paper. “Basically, what are the physics rules for changing the transverse OAM of a light pulse?”

In previous work, Milchberg, Hancock and colleagues described how they created and observed pulses of light that carry transverse OAM, and in a paper published in Physical Review Letters in 2021, they presented a theory that describes how to calculate this OAM and provides a roadmap for changing a STOV’s transverse OAM.

The consequences described in the team’s theory aren’t so different from the physics at play when kids are on a playground. When you spin a merry-go-round you change the angular momentum by pushing it, and the effectiveness of a push depends on where you apply the force—you get nothing from pushing inwards on the axle and the greatest change from pushing sideways on the outer edge. The mass of the merry-go-round and everything on it also impact the angular momentum. For instance, kids jumping off a moving merry-go-round carry away some of the angular momentum, making the merry-go-round easier to stop.

The team’s theory of the transverse OAM of light looks very similar to the physics governing the spin of a merry-go-round. However, their merry-go-round is a disk made of light energy laid out in one dimension of space and another of time instead of two spatial dimensions, and its axis is moving at the speed of light. Their theory predicts that pushing on different parts of a merry-go-round light pulse can change its transverse OAM by different amounts and that if a bit of light is scattered off a speck of dust and leaves the pulse then the pulse loses some transverse OAM with it.

The team focused on testing what happened when they gave the transverse OAM vortices a shove. But changing the transverse OAM of a light pulse isn’t as easy as giving a merry-go-round a solid push; there isn’t any matter to grab onto and apply a force. To change the transverse OAM of a light pulse, you need to flick its phase.

As light journeys through space, its phase naturally shifts, and how fast the phase changes depends on the index of refraction of the material that the light travels through. So Milchberg and the team predicted that if they could create a rapid change in the refractive index at selected locations in the pulse as it flew by, it would flick that portion of the pulse. However, if the entire pulse passes through the area with a new index of refraction, they predicted that there would be no change in OAM—like having someone on the opposite side of a merry-go-round trying to slow it down while you are trying to speed it up.

To test their theory, the team needed to develop the ability to flick a small section of a pulse moving at the speed of light. Luckily, Milchberg’s lab already had invented the appropriate tools. In multiple previous experiments, the group has manipulated light by using lasers for the rapid generation of plasmas—a phase of matter in which electrons have been torn free from their atoms. The process is useful because the plasma brings with it a new index of refraction.

In the new experiment, the team used a laser to make narrow columns of plasma, which they called transient wires, that are small enough and flash into existence quickly enough to target specific regions of the pulse mid-flight. The index of refraction of a transient wire plays the role of a child pushing the merry-go-round.

The researchers generated the transient wire and meticulously aligned all their beams so that the wire precisely intercepted the desired section of the OAM-carrying pulse. After part of the pulse passed through the wire and received a flick, the pulse reached a special optical pulse analyzer the team invented. As predicted, when the researchers analyzed the collected data, they found that the refractive index flick changed the pulse’s transverse OAM.

They then made slight adjustments in the orientation and timing of the transient wire to target different parts of the light pulse. The team performed multiple measurements with the transient wire crossing through the top and bottom of two types of pulses: STOVs that already carried transverse OAM and a second type called a Gaussian pulse without any OAM at all. For the two cases, corresponding to pushing an already spinning or a stationary merry-go-round, they found that the biggest push was achieved by applying the transient wire flick near the top and bottom edges of the light pulse. For each position, they also adjusted the timing of the transient wire laser on various runs so that different amounts of the pulse traveled through the plasma and the vortex received a different amount of kick.Researchers who previously generated vortices of light that they describe as “edge-first flying donuts” have now performed experiments where they disturb the path of the vortices mid-flight to study changes to their momentum.  Image credit: Intense Laser-Matter Interactions Lab, UMDResearchers who previously generated vortices of light that they describe as “edge-first flying donuts” have now performed experiments where they disturb the path of the vortices mid-flight to study changes to their momentum. Image credit: Intense Laser-Matter Interactions Lab, UMD

The team also showed that, like a merry-go-round, pushing with the spin adds OAM and pushing against it removes OAM. Since opposite edges of the optical merry-go-round are traveling in opposite directions, the plasma wire could fulfill both roles by changing its position even though it always pushed in the same direction. The group says the calculations they performed using their theory are in excellent agreement with the results from their experiment.

“It turns out that ultrafast plasma provides a precision test of our transverse OAM theory,” says Milchberg. “It registers a measurable perturbation to the pulse, but not so strong a perturbation that the pulse is completely messed up.”

The team plans to continue exploring the physics associated with transverse OAM. The techniques they have developed could provide new insights into how OAM changes over time during the interaction of an intense laser beam with matter (which is where Milchberg’s lab first discovered transverse OAM). The group plans to investigate applications of transverse OAM, such as encoding information into the swirling pulses of light. Their results from this experiment demonstrate that the naturally occurring fluctuations in the index of refraction of air are too slow to change a pulse’s transverse OAM and distort any information it is carrying.

“It's at an early stage in this research,” Hancock says. “It's hard to say where it will go. But it appears to have a lot of promise for basic physics and applications. Calling it exciting is an understatement.”

Story by Bailey Bedford

In addition to Milchberg, and Hancock, graduate student Andrew Goffin and UMD physics postdoctoral associate Sina Zahedpour were co-authors.

Philippov Awarded Sloan Research Fellowship

Assistant Professor Sasha Philippov is one of 126 scientists in the United States and Canada to receive a 2024 Sloan Research Fellowship.

Granted by the Alfred P. Sloan Foundation, the $75,000 award recognizes scientists who have made important research contributions and have demonstrated “the potential to revolutionize their fields of study.” The fellowship, introduced in 1955, is considered one of the most competitive and prestigious awards that an early-career scientist can receive. To date, 71 UMD faculty members have earned this distinction, including 14 from UMD’s College of Computer, Mathematical, and Natural Sciences since 2015.

Fellows are nominated by other scientists and selected by independent panels of senior scholars. Philippov was nominated by Eliot Quataert, a theoretical astrophysicist at Princeton University who said that Philippov’s research “stands out” from his peers covering similar topics.

“Sasha has a combination of physical intuition, physics depth, code development skills and computational acumen that is characteristic of the very best computational astrophysicists I have interacted with in my career,” Quataert said.Sasha PhilippovSasha Philippov

Philippov, who holds a Ph.D. in astrophysical sciences from Princeton, was previously named a NASA Einstein and Theoretical Astrophysics Center Fellow at UC Berkeley, where he completed a postdoctoral fellowship from 2017 to 2018.

After his postdoc, Philippov worked as an associate research scientist at the Simons Foundation’s Flatiron Institute, where he constructed the first models capable of explaining the mysterious coherent emission of pulsars—magnetized neutron stars that rapidly rotate.

Since joining UMD in 2022, Philippov has been busy with several research projects. He used simulations to show the production of gamma-ray flares from the black hole in galaxy M87, which was the first black hole to be pictured. He also demonstrated how kinetic effects change the flow of plasma and produced proof-of-concept simulations of radiative plasma turbulence.

Philippov also serves as deputy director of a Simons Foundation project called the Simons Collaboration on Extreme Electrodynamics of Compact Sources that models electrodynamic processes related to neutron stars and black holes.

Looking ahead, the two-year Sloan Research Fellowship will enable Philippov to delve deeper into the study of plasmas—hot, ionized gas that surrounds neutron stars and black holes, which he describes as “some of the most mysterious and exotic objects in the universe.”

Part of Philippov’s research will involve the study of magnetars, which are neutron stars with the strongest magnetic fields in the universe. He plans to use advanced 3D simulations to better understand the powerful magnetic flares that occur when pulsars release magnetic energy, enabling scientists to connect the dots between what is observed through telescopes and what is actually occurring at a magnetar’s surface.

He will also investigate black holes that accrete plasma “very efficiently,” meaning more plasma falls into those black holes than ones that accrete low-density plasma, such as the one in M87.

“Depending on how much falls in, the properties of the plasma are quite different because their temperatures and density are different,” Philippov explained.

For Philippov, more plasma means more opportunities to study neutrinos, which are weakly interacting particles that can be generated in the environment surrounding black holes. Philippov’s ultimate goal is to create models that explain how protons accelerate and end up producing neutrinos.

The timing is ideal, considering that the IceCube Neutrino Observatory at the South Pole recently detected neutrinos from a spiral galaxy called NGC 1068.

“There will be more observations with IceCube and future detectors, so it’s a good time to work on theoretical models,” Philippov said.

Ultimately, Philippov is excited to study the phenomena that help illuminate objects like black holes, which do not emit light on their own. In pictures of black holes, what we sometimes see are accretion disks, or rotating rings of plasma that create a glow.

“We haven’t learned much about black holes themselves yet, but we are able to learn a lot about how they shine,” Philippov said of the study of plasmas surrounding black holes. “Our goal is to understand how all the emission that we see is produced. We can see it, but we cannot really explain why and how, so that’s the underlying question.”

 

Original story by Emily C. Nunez: https://cmns.umd.edu/news-events/news/umd-astrophysicist-sasha-philippov-awarded-2024-sloan-research-fellowship

Losert Named MPower Professor

Wolfgang Losert has been named an MPower Professor.  Three professors from UMD and from the University of Maryland, Baltimore (UMB)  received this distinction from the University of Maryland Strategic Partnership: MPowering the State (MPower), which recognizes, incentivizes, and fosters collaborations between the two institutions.

Losert holds a joint appointment in physics and the Institute for Physical Science and Technology (IPST). He also holds an affiliate appointment in the Fischell Department of Bioengineering, andan adjunct appointment with the University of Maryland Medical System's Greenebaum Comprehensive Cancer Center. He is co-director of the National Cancer Institute-University of Maryland Partnership for Integrative Cancer Research. Losert's research — supported by $2 million-plus a year in funding for the past seven years — is at the convergence of physics, biology, and artificial intelligence and focuses on the nonlinear dynamics of living systems.
Wolfgang Losert. Credit: UMD/Lisa Helfert. Wolfgang Losert. Credit: UMD/Lisa Helfert.

In his research, Losert aims to discover emergent dynamic properties of complex systems at the interface of physics and biology. He currently leads a Multidisciplinary University Research Initiative program funded by the Air Force Office of Scientific Research that transformed our understanding of how cells sense their physical environment. He also serves as co-principal investigator on a Brain Research through Advancing Innovative Neurotechnologies (BRAIN) initiative center grant from the National Institutes of Health focused on information processing in sensory brain circuits.

Losert actively fosters cross-disciplinary interactions and new research and educational opportunities on campus and beyond. He helped launch and currently co-leads the American Physical Society Group on Data Science. He was part of a trans-university initiative of the Howard Hughes Medical Institute (called NEXUS) that developed new science and math courses for biology majors and pre-health care students that are being widely adopted. He led the development of and co-directs the NCI-UMD Partnership for Integrative Cancer Research, which provides UMD faculty members and graduate students the opportunity to tackle pressing problems in cancer research in collaboration with National Cancer Institute experts. 

A Fellow of the American Physical Society and the American Association for the Advancement of Science, Losert joined UMD in 2000 as an assistant professor and served as an associate dean in CMNS (2014-22) and as interim IPST director (2019-20). He earned his Ph.D. in physics from the City College of the City University of New York in 1998 and his diplom in applied physics from the Technical University of Munich in Germany in 1995.

Also selected were Jessica Magidson and Steven Prior from UMD and Lisa Berlin, Osamah Saeedi and James Polli from UMB.