Study On The Misalignment And Tiling Of The Gratings In Pulse Compression

The high-energy, short pulse laser systems provide chances to study the interaction of the light and the matter. At the same time, they also develop the study on inertial confinement fusion (ICF). To achieve high-energy, high-power, short pulse output, the chirped-pulse amplification (CPA) technology is used. It contains three stages: stretch, amplification and compression. In this paper, the space-time properties of pulsed super-Gaussian beam through grating-pair compressor in the case of finite beam size and the effect of the misalignment of the tiled grating to the pulse compression are analyzed.1 Starting with the Fourier angle spectrum of the pulsed beam, the analytical expression of the field distribution of the pulsed super-Gaussian beam passing through the grating-pair compressor in the case of finite beam size is derived. The results show that the high order dispersions stretch the pulse-width, distort the pulse and induce aberration to the pulse's space-time profile. When the pulsed super-Gaussian beam single passes through the grating-pair, the time-dependent spatial shift will be introduced in the output pulse by the transverse spectrum shift. The pulse front distortion increases with the distance between the incidence beam waist and the grating-pair. When double passed, the pulse-width obviously narrows. High-order dispersions bring the pulse wings. The third-order dispersion makes the pulse asymmetry, but the fourth-order dispersion makes the pulse distortion symmetry.2 The analytical expressions of the first- to fourth-order dispersions were derived, when there is misalignment between the two gratings of the compressor. When there is planar error, the compressed pulse is much wider and the SNR (signal noise ratio) decreases. The pulse distorts very much when single passing through the grating-pair. The pulse peak goes ahead and the wings appear when double passing through the grating-pair. When the grooves are unparallel, the position of the light-spot will shift due to the vertical spectrum displacement and the shift increases with the distance between the two gratings. So gratings with low groove density are superior to that of high density ones, if the groove misalignment is unavoidable.3 Theoretical models including groove-width difference and various angular errors are discussed for the optical design of the tiled-grating compressor. We propose some problems in the design of grating tiling. The duration variation of the compressed pulse at the focus is the primary effect for the large-scale laser beam. For a 140mm beam diameter and a 0.3ps pulse duration, we found that the groove-width difference Δd/d₁ must be less than 1.64×10^-4 in order to ensure stretch in duration below 20%. In addition, angular tilt errors between different segmental gratings in the tiled-grating must be less than 0.36mrad. The analytical method and design results are also suitable for the fabrication of a single grating with a large scale.All of above results have important referenced value to the adjustment of the parallelism of the grating-pair and the design of the tiled-grating.