Petawatt Laser Achieves Record Power

The Berkeley Lab Laser Accelerator (BELLA) laser system has generated a record petawatt of power in a pulse just 40 fs long at a pulse rate of 1 Hz — one pulse every second.

The BELLA design is based on years of laser plasma accelerator research performed by the US Department of Energy’s Lawrence Berkeley National Laboratory’s Accelerator and Fusion Research Div.’s (AFRD) Lasers and Optical Accelerator Systems Integrated Studies (LOASIS) program. In contrast to conventional accelerators, laser plasma accelerators produce electron density waves that move through a plasma, using laser beams to either heat and drill through a plume of gas or moving through plasma enclosed in a thin capillary in a crystalline block such as sapphire. Some of the plasma’s free electrons are trapped by the waves, accelerating them to very high energies within very short lengths.

The BELLA laser during construction. In the foreground, units of the front end stretch and amplify short, relatively weak laser pulses before further amplification in the long central chamber. Amplification is done by titanium sapphire crystals boosted by a dozen pump lasers. At the far end of the hall, the now highly energetic stretched pulse is compressed before being directed to BELLA’s electron-beam accelerator component. (Image: Roy Kaltschmidt, LBNL)

The first high-quality electron beams of 100 MeV were reported by LOASIS in 2004, followed by the first beam of 1 GeV in a 3.3-cm-long sapphire block in 2006.

The laser is expected to be the first plasma accelerator to produce a beam of electrons with an energy of 10 GeV. Unlike the Stanford Linear Accelerator Center (SLAC) — which achieved 50 GeV electron beams with traditional technology using a linear accelerator 2 miles long — the BELLA accelerator measures only 1 mile long and is supported by its laser system in an adjacent room.

Simulation of a laser wake field accelerator: Bunches of electrons (yellow and green) are injected and accelerated by surfing the plasma waves (blue surfaces) generated by a laser pulse. (Simulation: Cameron Geddes, LOASIS Program at NERSC)

The scientists have demonstrated the laser’s compressed output energy of 42.4 J in about 40 fs at 1 Hz. Its initial 1 PW of peak power is twice that of lasers capable of generating more intense pulses than those used by the entire US “at any instant time.” BELLA’s average power is just 42.4 W, the typical power for a household lightbulb. By packing the modest average power into a very short pulse, this high peak power can be achieved.

The laser system, developed by Thales of France, is fully integrated with Berkeley Lab equipment and personnel protection systems. Experiments to demonstrate BELLA’s ability to attain 10 GeV beams will begin this fall.

“BELLA will be an exceptional tool for advancing the physics of laser and matter interactions,” said Wim Leemans of Berkeley Lab’s AFRD, who conceived the laser system in 2006. “The laser’s peak power will give us access to new regimes, such as developing compact particle accelerators for high-energy physics, and tabletop free electron lasers for investigating materials and biological systems.”

For more information, visit: www.lbl.gov