Dynamic duo laser in on physics’ deepest questions

Rainer Grobe and Q. Charles Su have become more than colleagues. For the last 23 years, the Distinguished Professors of physics have worked side by side on the cutting edge of laser research while mentoring scores of undergraduate students at Illinois State University.

When either professor tries to describe their work as scientists, researchers, teachers, and founders of the Intense Laser Physics Theory Unit, the other interrupts. Nothing about these interruptions is rude, and they all fit a pattern. As one speaks, the other makes a quiet remark that brings laughter.

“Because we work together so intensively we probably have spent more time together than with our wives,” Grobe said.

The laughter has not always been welcome. “One new faculty member actually had to switch his office to another part of the building because it was always so loud here,” Grobe said, smiling. “The poor soul couldn’t work. We do laugh a lot. We like to laugh a lot about ourselves.”

Their work, however, is no joking matter. Last year, the Research Corporation for Science Advancement (RCSA) named them among the top physics scholars in the country. The pair received RCSA’s annual Singular Exceptional Endeavors of Discovery (SEED) Award and $50,000 for “exceptionally creative new research or educational activities with potential high impact.”

This is just the latest award in a career richly rewarded by prominent institutions, such as the National Science Foundation (NSF) and U.S. Department of Energy. Since 1996, Grobe and Su have received more than $2.8 million in research funding through the competitive granting process. It basically makes their funding level among the highest in the nation for theoretical atomic physics for undergraduate-only institutions.

So what, besides levity, goes on in the Intense Laser Physics Theory Unit located in Moulton Hall? It’s where Grobe and Su research the interaction of laser light with matter. One current project involves trying to understand how light interacts with the vacuum and using the properties of matter to impact the property of the light itself.

“It’s all about this two-way stream of manipulating matter with external laser light,” Grobe said. “We are studying laser-induced vacuum breakdown using computer simulation.”

Su said it makes sense to perceive the vacuum as an empty volume of space, but he added that things change when that space is probed with an intense laser field. “Quite remarkably, when laser intensity exceeds a certain threshold value, the vacuum becomes unstable—like blowing too much air into a balloon.” This causes the vacuum to decay, “like bursting a balloon.”

Such work, he said, has revealed new aspects of the process that may serve as a guide to possible future experiments related to vacuum breakdown.

Grobe and Su’s SEED Award was for their work “A Non-Perturbative Approach to Identify Electron-Positron Pairs in Relativistic Interaction Zones.” Grobe and Su proposed several independent ways to determine what kinds of particles—electrons or positrons—are produced and where.

“With these ways of detecting particles, we can, for the first time, step inside the matter creation zone to see pair creation as it happens,” Su said. “In an initial investigation, we found, very much to our surprise, in locations where the force field is strongest, not a single particle is created.”

As often happens with their research, this work leads to more fascinating questions that will need to be examined. The researchers explore subjects in the very early stage of early discovery. “It’s more like curiosity,” Su said. “We’re not thinking of those (real-world) applications at the time of a discovery. It’s more like, ‘I want to find out what that is and how it works.’”

One of their former students, Samantha Norris ’16, said her favorite part about working with the professors was when at the end of long days they would come up with a nice graph or equation describing how electrons are born out of thin air, or how they react to a particular force. “It was then that we would step back and realize that we were the first ones in the world to understand this particular phenomenon,” Norris said.

Most semesters Su and Grobe work with seven or eight undergraduate students on research projects. The mentoring starts as early as a student’s freshman year and involves one-on-one instruction that is a natural extension of classroom teaching.

“What makes ISU special is we have a nice marriage between good teaching and good scholarship,” Su said. “And I think to motivate yourself to be a better teacher to make these undergraduate students understand is somehow a challenge.

“It forces you to come down from your research level and to explain. That sometimes helps us to articulate precisely our problems, and then it helps to solve those problems.”

Norris worked in Su and Grobe’s lab while pursuing a bachelor’s degree in physics. She is now a graduate student at Cornell University.

“Of course Dr. Su and Dr. Grobe taught me a lot about physics, computer modelling, math, and all of the things that come with a research-focused undergrad education in physics,” Norris said. “What I didn’t realize until after graduation is how much they taught me how to be a better scientist and researcher, and how to think critically about the problems I encounter.”

Norris said the professors encouraged her to ask, “Why are things done this way?” Their influence has caused her to question current techniques and methods as a grad student, which has proved to be invaluable in trying to make new developments. It was also invaluable for Norris to have published several papers during her time at Illinois State.

One of her favorite things about Su and Grobe is their ability to explain things in an intuitive way. “Instead of writing equations to model a quantum mechanical wave function, their favorite analogy was a bag of bumblebees,” Norris said. “As in, ‘Some are moving left, some are moving right, just like electrons.’”

Both men simplify complex topics to help students learn efficiently.

“We hate the show business when you hide behind jargon,” Grobe said. “Often in the sciences, insecure people hide themselves behind jargon.”

Many of the lessons Grobe and Su share with their students, they learned from their mentor, Professor Joe Eberly at the University of Rochester in New York. They met at that university in the early 1990s while Su, a native of China, was a graduate student, and Grobe, who is from Germany, was a postdoctoral research fellow. Su came to Illinois State in 1994, and Grobe followed in 1995.

Eberly taught them how to think about physics. “The Eberly approach is throwing away everything which is irrelevant and focusing really on the very essentials,” Grobe said. “And, if you do this, then you realize that there are suddenly so many open fundamental questions nobody actually knows the answer to.”

Their projects can span the length of a career to investigate. That decades-long arc from research to practical application is nothing new to the duo or to other practitioners of physics.

Su cited Albert Einstein—whose early work inspired the development of a number of modern innovations including scanners, GPS navigation, and solar energy technology—for his theory of relativity and for his discovery of the law of the photoelectric effect. Best known for his work on relativity, Einstein received the Nobel Prize in Physics in 1921 for figuring out the photoelectric effect, a subject he was writing about as far back as 1905.

“We probably will not finish either,” Grobe said. “This will never end. Look at Professor Eberly: He is 82 years old and still doing it because he has the drive. He is still active as ever.”

They also believe that dissent and questioning from their students is healthy.

“The only difference between them and us is we have been indoctrinated with this stuff much, much longer than they have, and that’s the only difference,” Grobe said. “We are not smarter than they are, not more intelligent. It’s just that we have more knowledge. If a student points out that we are wrong, that’s fantastic. We love that.”

Reid Gramm, a sophomore physics engineering major and mathematics minor, began researching with Su and Grobe his freshman year despite knowing very little about physics.

Gramm, who has already had one journal publication, praised the unique opportunities for undergrads studying physics at Illinois State.

“Since there is no physics graduate program at ISU, student research assistant positions are available exclusively to undergraduates—something rare at other physics departments,” Gramm said. “Dr. Su and Dr. Grobe are great at seeking out students for research, and that’s how they got me hooked.

“They want to keep science moving forward. Students like myself are lucky to be able to join them on their many journeys toward new unknowns.”

John Moody can be reached at jemoody2@IllinoisState.edu.