Fifty million dollars can do a lot of good for the world, and for a team of researchers at the University of Michigan, that good comes from building a lab facility that currently houses the most powerful laser in the United States.
Based on the work of Gérard Mourou, founding director of the Center for Ultrafast Optical Science (CUOS) at Michigan Engineering, a team of U-M researchers submitted a proposal in 2019 to the National Science Foundation (NSF) to upgrade its HERCULES laser system, which at the time was the highest-focused intensity laser system in the world. Intensity is a measure of total power transferred per area, and the world record is now held by the Center for Relativistic Laser Science (CoReLS) in Gwangju, South Korea.
Despite losing its world record status, HERCULES is still housed on the University’s North Campus. Upon receiving a $40 million grant from the NSF in 2019, the University upgraded HERCULES and built the “Zettawat Equivalent Ultrashort pulse laser System,” or ZEUS, which is now the most powerful laser in the nation.
But what does it mean for a laser to be “the most powerful?” Karl Krushelnick, engineering professor and CUOS director, sat down with The Michigan Daily to get to the bottom of it.
Krushelnick said ZEUS is not the kind of laser you see in movies drilling holes in the wall, and it won’t look anything like a lightsaber from Star Wars. The laser emits radiation when it’s fired, according to Krushelnick, so researchers have to take certain precautions while using it. Despite that, he said the laser is not dangerous in the ways people might expect. The laser is fired in a highly secured environment, and only for fractions of a second at a time, so Krushelnick said any efforts to weaponize the laser would be extremely hard to do.
Krushelnick broke down how to increase power emitted by the laser by explaining that power is equal to energy divided by time. Thus, researchers have two options: either increase the energy emitted, or reduce the amount of time that the laser fires. In the case of Krushelnick and his team, they chose the latter.
“The laser pulses that we use for ZEUS have extremely short pulses,” Krushelnick said. “They’re 25 femtoseconds, and a femtosecond is 10 to the minus 15 seconds.”
A femtosecond is one quadrillionth of a second — a period so short that the research team must use a series of speciality cameras just to record their experiments.
ZEUS Research Scientist John Nees, walking through the space where the laser is housed in Engineering Research Building 1 on North Campus, said the lab is about the size of half a football field. Because the laser is only fired for a duration of femtoseconds, it is fired in a vacuum so that it can be properly observed. Nees said since the laser pulse is so short, if the laser were not fired in a vacuum it would self-combust.
“It’ll collapse itself in the filaments and burn everything, but by keeping it in vacuum the beam can propagate smoothly,” Nees said.
Krushelnick said the research team is still testing the laser and running preliminary experiments with it to prepare for more frequent use in the coming years. The research is fundamental and theoretical in its nature, meaning the work Krushelnick and his team does won’t appear in the commercial world anytime soon.
“In our case, we’re still doing basic research,” Krushelnick said. “We’re just trying to make these beams. Mainly we want to be able to take the beams and make them more compact and make higher energy beams in a smaller space using a laser and then to make them eventually more available.”
Krushelnick said when the laser is ready for other scientists to use, a board of third-party adjudicators will be responsible for evaluating applications from researchers all over the world who want to use the laser for their experiments and research. He said both the NSF and the University hope to test several different research theses with ZEUS in the coming years, so they will be granting access to a host of diverse proposals.
“The National Science Foundation wants as many people as possible to use the facility and have access to it and there’s a community already that exists who are interested in and will apply to use the facility,” Krushelnick said. “But then the NSF wants people from outside that community as well who don’t necessarily know that their research could be helped by the facility. We’re trying to approach biologists and chemists and material scientists and say, ‘Well, you can do this, you can use this facility.’”
Krushelnick said while the research is theoretical, there are real-world applications for studies involving the laser.
“The kind of beams that we make actually make super high resolution x-ray images, and that has an application for medicine,” Krushelnick said. “We also make ions, so we’re also trying to control the ion beams so that we can use them for cancer therapy. Ion radiotherapy is one of the most effective ways of treating cancer.”
When asked about how students are involved in this research, Krushelnick indicated that the majority of the research and work surrounding the laser has been completed by his staff, with the assistance of graduate students. One undergraduate student also helped out during the early days of the ZEUS laser, Krushelnick added.
Engineering senior Carl Gerisch was the undergraduate who worked with the laser last year. Gerisch told The Daily that his first project with the laser involved working with the angle of the mirrors to adjust how they reflect light and beams.
“They needed a light source that they could use to align devices,” Gerisch said. “You have to have everything lined up perfectly. If it’s a slight angle wrong then (the laser) will miss a mirror way down the chain … I just aligned a basic light source that is at the same wavelength as the ZEUS laser and … It doesn’t expand or contract so they could use that to align a bunch of different components.”
Gerisch said working with the laser was an incredible experience. He said the research helped him apply the electrical engineering principles he has learned in his classes and contextualize his coursework in the real world.
“There’s a lot of math, there’s a lot of calculations, but then when you actually take it to the lab and do research, it becomes real, and you can see the applications of what you’re learning and you can see what the meaning behind it is,” Gerisch said.
Daily Staff Reporter Bobby Housel can be reached at bhousel@umich.edu.