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

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.