Spatiotemporal Dynamics in the Near-Field of Mosaic Grating Compressors with Different Pulse Durations for Kilojoule–petawatt Laser System

In kilojoule-petawatt laser systems, grating mosaic is a common approach for fabricating meter-sized multilayer dielectric gratings (MLDGs) [11-14], but the imperfections such as mosaic gap increase the risk of damage to the final grating. It has been revealed that the short-pulse damage initiation in such grating exhibits a strong dependence on laser intensity [31,32,39]. In this paper, we investigate the three-dimensional near-field dynamics at the final grating of the mosaic grating compressors for both Fourier-transform-limited (FTL) and chirped pulses, based on the single-pass symmetric and asymmetric configurations. In the symmetric configuration, the near-field intensity fluctuations caused by errors of the second and third gratings (G2-G3) are effectively smoothed for FTL pulse, which is attributed to frequency-dependence of these fluctuations induced by the spatial dispersion between G2-G3. For chirped pulses, the instantaneous intensity distribution directly reflects the spatial profiles of corresponding chirped frequency components, thereby eliminating the smoothing effect, and the cross-influences of errors from all upstream gratings (G1-G2-G3) significantly deteriorated the intensity fluctuations. The asymmetric configuration introduces uncompensated spatial dispersion in the G4 near-field, results in frequency-dependence for the intensity fluctuations induced by G1 errors, hence the intensity distributions are smoothed for the FTL pulse. For the chirped pulse, this smoothing effect is similarly absent, and the intensity deterioration caused by cross-influences of G1-G2-G3 errors remains unmitigated. These results provide a crucial reference for configuration optimization of mosaic grating compressors.