Zhang Yinrui, Huang Yuan, Zhong Zheqiang, Zhang Bin
Appl Opt. 2020 May 20;59(15):4624-4633. doi: 10.1364/AO.389738.
In order to improve the irradiation uniformity on the target plane and reduce the parametric backscattering in indirect-drive inertial confinement fusion facilities, a rapid polarization rotation smoothing scheme is proposed. In this scheme, there is a central wavelength shift between adjacent beams in a laser quad. Two of these beams are transformed into left-rotating circularly polarized beams by using polarization control plates, and the other two are transformed into right-rotating circularly polarized beams. Moreover, conjugate spiral phase plates are adopted to transform the beams into conjugate Laguerre-Gaussian beams. As a result of the frequency beat among the beams with counter-rotating polarization and conjugate spiral phases, both the intensity distribution and polarization of the focal spot would rotate rapidly on the picosecond timescale. The physical model of the rapid polarization rotation smoothing scheme is built up, and the smoothing performance affected by the parameters of spiral phase plates, polarization control errors, wavelength shift, and wavefront distortions is analyzed in detail. The results indicate that the rapid polarization rotation smoothing scheme has a relatively wide tolerance to the polarization errors and the spiral phase plates, and can improve the smoothing performance effectively with the combination of the smoothing by spectral dispersion scheme.
为了提高间接驱动惯性约束聚变装置中靶平面上的辐照均匀性并减少参数背散射，提出了一种快速偏振旋转平滑方案。在该方案中，激光四路中的相邻光束之间存在中心波长偏移。其中两束光通过偏振控制板转换为左旋圆偏振光束，另外两束光转换为右旋圆偏振光束。此外，采用共轭螺旋相位板将光束转换为共轭拉盖尔 - 高斯光束。由于具有反向旋转偏振和共轭螺旋相位的光束之间的拍频，焦斑的强度分布和偏振都会在皮秒时间尺度上快速旋转。建立了快速偏振旋转平滑方案的物理模型，并详细分析了螺旋相位板参数、偏振控制误差、波长偏移和波前畸变对平滑性能的影响。结果表明，快速偏振旋转平滑方案对偏振误差和螺旋相位板具有相对较宽的容差，并且与光谱色散平滑方案相结合可以有效提高平滑性能。
