Zhang to Explore Novel Property of Laser-Induced Plasmas with ECLIPSE Grant
Just as flicking on a flashlight reveals the objects in a dark room, pointing a laser at a cloud of gas can reveal a lot about the atoms and molecules floating in it.
Zhili Zhang, a B. Ray Thompson professor in the Department of Mechanical, Aerospace, and Biomedical Engineering, has been using lasers to research gases for more than 20 years.
"When you focus a laser in a gas medium, it creates a small plasma that reflects the gas's properties," Zhang explained. "We use the laser-material interactions to probe qualities like elemental species, temperature, pressure, magnetism, and particle velocity."
Typically, scientists shine lasers into gases for a nanosecond (one billionth of a second) at a time to produce small, intense plasmas that can be used to study phenomena like fuel combustion or the airflow around hypersonic jets (which travel at speeds at or above Mach 5).
However, in a recent study funded by the National Science Foundation (NSF), Zhang made an incredible discovery.
He found that even shorter laser bursts—ranging from one quadrillionth to one trillionth of a second—create thin, stable channels of plasma called filaments that can still be used to study gases. In fact, those pulses are so short that no molecular collisions can happen while the laser is on.
"You can literally take a snapshot of the molecules," Zhang said. "It's the instantaneous velocity and temperature of all the species in the gas."
Even more incredible, Zhang found that by changing the dynamics of these extremely brief pulses, he can induce plasmas far from the source of the light. How far?
"These filaments can propagate kilometers away from the laser," said Zhang. "It is an astonishing phenomenon."
Funding for Fundamental Plasma Science
This fall, Zhang received a $376,000 grant from the NSF to further investigate the laser-induced plasma filaments. The grant comes from the ECosystem for Leading Innovation in Plasma Science and Engineering (ECLIPSE) program, which emphasizes fundamental plasma science to impact broader technological problems.
For the next three years, Zhang will investigate how different laser parameters like light intensity, wavelength or color, and repetition rate impact the filament and its ability to propagate over long distances. Understanding how to make and maintain the long-distance plasmas could allow for remote detection of magnetic fields, such as those that form around power generators, among other uses.
Zhang will also create a physics-informed neural network to make plasma kinetic models, which he will validate with experimental measurements.
"AIs are super powerful right now, but they need data," Zhang said. "You need to measure the gas properties accurately so you can make predictions."
Involving Students in Plasma Research
Zhang's ECLIPSE grant also includes funding for several students, reflecting his desire to broaden student participation in plasma physics research.
"Involving the students in research is very important," he said. "The textbook hasn't changed in maybe 30 years, but there are all kinds of new techniques, and students should learn them. It gives them the creativity to tackle problems in different ways. Seeing students thinking outside of the box is very, very rewarding for me."
In addition to the work students do in his lab on UT's Knoxville campus, Zhang enjoys bringing them to the UT Space Institute (UTSI) in Tullahoma, Tennessee, where he has many collaborators researching hypersonic vehicles. Zhang brings his equipment and lab members to UTSI's wind tunnels multiple times each year to characterize the airflow around jets undergoing tests.
"In engineering, when we produce results, we want to use them. I want to see my work make a real-world impact," Zhang said. "At UT, I can develop a new diagnostic tool or fundamental laser technique and then test it in a real-world environment. I don't think there are many universities that have the kind of capability."
Provided by University of Tennessee at Knoxville