Dataset for Characteristics and mitigation analysis of near-field modulation of mosaic grating compressor for kilojoule petawatt laser system

The implement of chirped-pulse amplification (CPA) technology overcomes the damage limitation of the amplifiers, enabling the generation of kilojoule-petawatt (PW) lasers, but the damage of the last grating in the compressor becomes a critical constraint to further enhance the output performance. The near-field intensity and fluence modulations induced by upstream grating imperfections are the main reason increasing the risk of damage to the last grating. SG-II UP PW picosecond system employs meter-sized gratings fabricated by optical mosaic approach, the grating imperfections can be classified into two categories, the first is amplitude errors such as mosaic gaps of grating, which is originated from the movement of substrate during multiple-exposure process, the diffraction effects of grating gaps would induce severe near-field modulation. The second is diffracted wavefront errors caused by the imperfect exposure system and surface, it would result in near-field modulation during the propagation within the compressor, which is known as the Talbot effect. In this study, according to the characteristics of near-field modulation in the last grating of single-pass mosaic grating compressor, we investigate the mitigation method and control requirement for grating imperfections. The impacts of position misalignment of all upstream grating gaps on near-field modulation are evaluated, and the beam-shaping method utilized a nested inverted super-Gaussian profile is employed to mitigate the fluence modulation. Based on the Talbot effect, the mid-spatial frequency (MSF) wavefront errors of gratings are the primary factor inducing the near-field modulation under the working distance. To quantitatively analyze the near-field modulation caused by MSF wavefront errors, the random power spectral density (PSD) curves are employed to generate simulated wavefront distributions. The position misalignment of the second and third grating (G2-G3) gaps causes negligible impacts on the near-field modulation, which originates from the transverse spatial chirp between G2-G3, it causes the gap positions of these gratings sweep with beam frequency, thereby the influences of position misalignment are shadowed. Meanwhile, due to the frequency-dependent positions of the second and third grating gaps, the resulting near-field fluence modulations are smoothed, whereas the first grating gap result in severe modulation. To mitigate the fluence modulation induced by the first grating gap, the beam-shaping method is employed to shadow it, utilizing a nested inverted super-Gaussian profile to achieve a low energy loss, which comprises the inner fourth-order and outer tenth-order inverted super-Gaussian layer, the fluence modulation can be mitigated below 1.2 by parameter optimization. Additionally, the control requirements of MSF wavefront errors for different upstream gratings are determined with a target near-field modulation index of 1.2. In conclusion, this study summarizes the impacts of upstream grating imperfections on the near-field at the last grating of compressor for kilojoule petawatt laser system, based on the characteristics of the near-field modulations, the mitigation method and control requirement for the mosaic gaps and wavefront errors are investigated, respectively. Furthermore, it is noteworthy that the frequency-dependent errors of compressor can deteriorate the temporal properties, which necessitates thorough investigation.