New laser will put US back in the game of high-peak-power devices

With a $16 million grant from NSF, the University of Michigan will build a laser that has the highest peak power of any laser in the US. The 3 petawatt system is expected to advance fundamental and applied research with work ranging from testing fundamental quantum electrodynamics to developing lower-cost proton beams for cancer therapy.

The ZEUS laser will be an upgrade of Michigan’s HERCULES 500 terawatt laser, which has been in operation since 2006. It will be open to researchers from other institutions on a competitive basis when completed in about three years, says Karl Krushelnick, director of the university’s Gérard Mourou Center for Ultrafast Optical Science. Center namesake Mourou, an emeritus University of Michigan professor, shared half of the 2018 Nobel Prize in Physics with Donna Strickland of the University of Waterloo in Ontario for their development of chirped pulse amplification, a technology that enabled construction of compact high-power lasers (see Physics Today, December 2018, page 18 ).

The US’s top high-power lasers, both rated at 1 PW, are located at Lawrence Berkeley National Laboratory and the University of Texas at Austin. Each is dedicated to a specific line of research; ZEUS will be a general-purpose machine.

Although the US built the world’s first petawatt laser in 1996, it hasn’t kept pace with other parts of the world. The current world record of 5.3 PW is held by China’s Shanghai Superintense Ultrafast Laser Facility. In Europe, three 10 PW systems are being built in Romania and the Czech Republic as part of the European Union’s €850 million ($938 million) Extreme Light Infrastructure program. China has longer-term plans for a 100 PW machine.

A 2018 National Academies of Science, Engineering, and Medicine report called for a national strategy in support of the science, technologies, and applications of intense and ultrashort lasers. The University of Michigan laser project was one of several midscale research infrastructure projects selected under a February NSF solicitation.

One experiment already planned for ZEUS will probe quantum electrodynamics by colliding a laser beam with an electron beam. Pulses from the laser should concentrate enough power per unit area to spur the creation of electron–positron pairs in the vacuum. Sensors on the walls of the chamber will detect the high-energy antimatter. A 1998 experiment at SLAC measured some pair output by colliding a 50 GeV electron beam with a laser, but scientists have had trouble carrying out the experiment with a very intense laser system, Krushelnick says.

Quantum electrodynamics also predicts that the electric field from the laser could become so strong that it would make seemingly empty space behave like a lens for light (see Physics Today, March 2014, page 16 ).

Outside of fundamental research, medical physicists suspect that proton beams driven by high-power lasers could have sufficient energy to treat deep-seated tumors. If petawatt lasers on the scale of ZEUS are further developed and engineered, they may replace costly accelerators used at today’s proton-beam cancer-therapy centers, enabling more hospitals to acquire them (see the article by Jerimy Polf and Katia Parodi, Physics Today, October 2015, page 28 ). In another potential application, a high-power beam could generate high-energy x rays capable of probing inside shipping containers to determine whether a high-density mass is lead or a fissile material.

At 20 femtoseconds in length, the ZEUS pulses will be ultrashort. In experiments known as pump–probe measurements, the use of short-duration laser, radiation, and particle beams enables observation of the dynamics of matter at those time scales, says Krushelnick.

In full-power mode, ZEUS will be able to fire a shot per minute; pulses at a rate of 5 Hz will be available in the terawatt regime.