Researchers work on a fiber-laser beam-combining experiment

Researchers work on a fiber-laser coherent beam-combining experiment meant to combine high average power and high peak power.

LPAs require high peak laser power to drive the plasma wakefields for acceleration. Lasers like the BELLA Petawatt produce tremendous power at a pulse rate once every second. Future LPAs will require high peak power at a high repetition rate, giving high average power. Surveying emerging laser technologies in search of the best approaches, we began exploring fiber lasers, a promising and rapidly developing technology. Fiber lasers are the most efficient high-power lasers, representing a highly efficient, compact, and robust monolithic laser architecture with excellent thermal management.

Our collaboration with colleagues at the University of Michigan, Lawrence Livermore National Laboratory, and ATAP’s Berkeley Accelerator Controls and Instrumentation Program is developing a fundamentally new approach called coherent beam combining. It melds the individually low-powered pulses from many fiber-optic lasers into a single high-quality pulse coherent in space and time (as if from a single laser). It is energetic enough to drive an LPA—and does this a thousand times a second.

The pulse durations of today’s fiber lasers are longer than those needed by LPAs. Our comprehensive solution includes spectral combining and shortening the fiber laser pulses to tens of femtoseconds to meet accelerator needs.

Diagram of coherent beam combining, with inset showing several red laser beams in a Z shape as they go through some of it

By incorporating coherent combination schemes in the spectral, spatial, and temporal domain, a single high-peak-power laser pulse can be generated out of many mJ-class beamlets, at multi-kHz repetition rates.

We look to this approach for a future facility, called kBELLA for its kHz repetition rate and kW average power, that will push the power limits of ultrafast lasers from today’s tens of watts to kilowatts and beyond, enabling LPAs and other high-impact laser applications in discovery science, medicine, and industry.