Smoothing of small on-target spots produced by frequency-tripled beams using lens arrayand spectral dispersion
采用透镜列阵与光谱色散改善三倍频小焦斑辐照均匀性

The performances of the smoothing of small target spots with a lens array (LA) and two-dimensional smoothing by spectral dispersion (2D SSD) in frequency-tripled high-power laser driver are numerically studied. Intensity distributions and spatial power spectra of the spots are analyzed. Simulative results show that LA can reduce the near-field nonuniformity of the beam and control the envelope of on-target intensity distribution. The 2D SSD has obvious effects in eliminating high-contrast intensity modulation, even in the case that the spots are very small. The results indicate that SSD mainly smoothes the intensity modulation at low-to-middle spatial frequency for small spots, and this would lead to the modifying of the spot profile, while for large spots, SSD sweeps the fine speckle structure to reduce nonuniformity at middle-to-high frequency. These results are valuable for choosing the suitable beam smoothing method in indirect-drive experiment.