Analysis of the smoothing performance of a rapid polarization rotation smoothing scheme.

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.