Using the Petawat laser from the Center for Relativity Laser Science (CoReLS), a Korean Institute of Basic Science, the researchers demonstrated a record high laser pulse intensity of more than 1023 W/cm2. It took more than a decade to reach this laser intensity, ten times the record set by a team at the University of Michigan in 2004. These ultra-high-intensity light pulses will allow people to explore complex interactions between light and matter in ways previously impossible.
This powerful laser can be used to study phenomena considered high-power cosmic rays that have more energy than gigabit (1015) electron volts (eV). Although scientists know that these rays come from somewhere outside our solar system, it remains a long-standing mystery how and what formed them.
Chang Hee Nam, director of CoReLS and a professor at the Gwangju Institute of Technology, said: “This high-intensity laser will allow us to study astrophysical phenomena such as electron-photons and photon scattering in the laboratory. “We can use it to experiment with testing and acquiring theoretical ideas, some of which was first put forward nearly a century ago.”
In Optics, a high-impact research journal of the Optical Society (OSA), researchers report on years of efforts to increase the pulse intensity of lasers in CoReLS lasers. Studying the physical interactions of lasers requires a tightly focused laser, and researchers can focus laser pulses on spots just over a micron in size, less than one-fiftieth of the diameter of a human hair. The new record-breaking laser is equivalent to focusing all the light from the sun to Earth into a 10-micron spot.
The new achievement extends previous work by showing a Ti: Sapphire-based femtosecond laser system that produces 4 petawatt (PW) pulses that last less than 20 femtoseconds while focusing on a 1-micron point. The laser was reported in 2017 to produce about 1,000 times as much power as all the electricity on Earth in a laser pulse that lasts only two hundred trillionths of a second.
To produce a high-intensity laser pulse at the target, the resulting light pulse must be focused extremely tightly. In the new work, researchers used an adaptive optical system to accurately compensate for optical distortion. The system involves a deformable mirror with a controlled, reflective surface shape to accurately correct the laser’s distortion and produce a beam of light with very good control of the front of the wave. They then use a large off-axis parabolic mirror to achieve an extremely tight focus. This process requires fine handling of the focusing optical system.
Researchers are using these high-intensity pulses to generate electrons with more than 1 GeV (109 eV) of energy and to work with nonlinear systems, one of which collides with hundreds of laser photons at the same time. This process is a strong field quantum electrodynamic called nonlinear Compton scattering, which is thought to contribute to the production of very high-energy cosmic rays.
They will also use radiation pressure from ultra-high-intensity lasers to accelerate protons. Understanding how this process occurs could help develop a new laser-based proton source for cancer treatment. The sources used in today’s radiation therapy are generated using accelerators and require a huge radiation shield. Laser-driven proton sources are expected to reduce system costs and become more widely acceptable to patients.
Researchers continue to develop new ideas to increase laser intensity without significantly increasing the size of the laser system. One way to achieve this is to find a new way to reduce laser pulse time. With lasers with peak power from 1 to 10 PW now in service and several facilities up to 100 PW in the pipeline, there is no doubt that high-intensity physics will make great progress shortly.