多光束消偏振叠加对焦斑特性的影响

Influence of depolarized superposition of multi-beams on characteristics of focal spot

在惯性约束聚变(ICF)驱动器设计中,利用正交偏振板改变光束内部偏振态,实现靶面消相干叠加,以进一步改善靶面辐照均匀性。建立了正交偏振板的透过率函数,分别对单光束和多光束叠加两种情况下的焦斑偏振特性及均匀性进行数值模拟和分析。结果表明,利用正交偏振板能较好地实现光束消偏振叠加,焦斑在时间统计上表现为部分偏振光;采用正交偏振板互补组合方式时,消偏振效果随偏振板单元数的变化不敏感,因而可以选取单元数较少的正交偏振板,以降低对加工工艺的要求。

In inertial confinement fusion （ICF） driver design, by varying the polarization of beamlets, a orthogonal polarization control plate （OPCP） is applied to achieve incoherent superposition of beamlets on target for improving illumination uniformity. The model for the transmittance function of OPCP was built up. The depolarizing characteristics and uniformity of focal spot of single beam and of multi-beam superposition were simulated numerically and analyzed. The effects of the element number of OPCP on the characteristics of focal spot were further discussed. The results show that, the depolarized laser beam could be achieved by using the orthogonal polarization control plate, and the light field exhibits partially polarization in time scale. The complementary combination of orthogonal PCPs is better for the superposition of depolarized multi-beams. Moreover, the depolarizing effect remains almost unchanged with the element number of OPCP. Thus, the number of elements could be fewer to reduce requirements of processing technology.