采用透镜列阵与光谱色散改善三倍频小焦斑辐照均匀性

Smoothing of small on-target spots produced by frequency-tripled beams using lens array and spectral dispersion

通过数值模拟研究了高功率激光驱动器的光束均匀辐照情况,分析了三倍频激光辐照下小焦斑的光强分布及空间功率谱.采用透镜列阵可降低光束近场畸变的影响并控制靶面焦斑的包络形状;采用二维光谱色散匀滑技术可明显地消除焦斑内部大反衬度的强度调制,且该方法在焦斑非常小的情况下也仍然有效.大量的数值模拟结果表明,光谱色散匀滑技术应用于尺寸不同的焦斑时,其效果是有差异的.对大焦斑而言,光谱色散匀滑主要抹平其内部细密的条纹,即消除中高空间频率范围的强度调制;对小焦斑而言,光谱色散匀滑主要消除中低空间频率范围的强度调制,故将影响焦斑的整体包络形状.本文所得的数值结果对间接驱动实验中激光束匀滑方案的选择和优化具有参考价值.

The performances of the smoothing of small target spots with a lens array （LA） and two-dimensional smoothing by spectral dispersion （2-D 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 2-D 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.