Wavefront Measurement for Laser-Guiding Diagnostic

The wavefront of a short laser pulse after interaction in a laser‐plasma accelerator (LPA) was measured to diagnose laser‐guiding quality. Experiments were performed on a 100 TW class laser at the LOASIS facility of LBNL using a hydrogen‐filled capillary discharge waveguide. Laser‐guiding with a pre‐formed plasma channel allows the laser pulse to propagate over many Rayleigh lengths at high intensity and is crucial to accelerate electrons to the highest possible energy. Efficient coupling of laser energy into the plasma is realized when the laser and the channel satisfy a matched guiding condition, in which the wavefront remains flat within the channel. Using a wavefront sensor, the laser‐guiding quality was diagnosed based on the wavefront of the laser pulse exiting the plasma channel. This wavefront diagnostic will contribute to achieving controlled, matched guiding in future experiments.