Performance improvement of a 200TW/1Hz Ti:sapphire laser for laser wakefield electron accelerator

Abstract For investigations on laser wakefield electron acceleration, there is a strong demand for driving laser exhibiting high stability and good spatial-temporal quality. Here we present an upgraded 200TW/1Hz Ti:sapphire laser with following key characteristics. The fluctuation of pulse energy and beam pointing for consecutive 5400 pulses in 90 min are as low as 0.55% and 1.5μrad respectively. The compressed pulse duration is 23.7 fs, which is about 1.1 times of the Fourier-transform limit. The focal spot obtained by an f/30 off-axis parabolic mirror is 54 μm × 52 μm at 1/e2, which is very close to the diffraction limit. Moreover, in the laser wakefield electron acceleration experiments driven by this upgraded 200TW/1Hz laser, quasi-mono-energetic electron beams are reproduced in consecutive shots. For successive 300 shots, the average peak energy of produced electron beams is 667 MeV, and the peak energy fluctuation is only 3.4%. The progresses on both driving laser and laser wakefield electron acceleration make the realization of compact X-ray free electron laser possible.