In-situ measurement and compensation of complex spatio-temporal couplings in ultra-intense lasers

Diffraction wavefront errors of large-scale Treacy compressors may induce complex spatio-temporal couplings (CSTCs) in chirped pulse amplification and degrade the quality of the pulsed beam in both near and far fields. This problem is particularly pronounced in petawatt laser facilities that require tiled compressor gratings. Here, to the best of our knowledge, we present the first in-situ measurement method named pseudo lateral shearing interferometry (PLSI) for the CSTC wavefront error and manufacture a continuous phase plate (CPP) according to the measurement to reduce the distortion. A Shark-Hartmann wavefront sensor is used to characterize wavefronts of the entire system at two different wavelengths, and the CSTC wavefront error can be reconstructed similarly to lateral shearing interferometry (LSI). Our approach strongly reduces systematic errors and the impact of other optics. The root-mean-square (RMS) value of the resulting error is 40 nm in a single measurement, and the day-to-day repeatability is 55 nm. The employed CPP reduces the peak-to-valley (PV) value of the CSTC wavefront error from 675 to 312 nm, and the focused peak intensity is improved by 51%.