Polarization state control for high peak power applications

Abstract: Numerous applications in the extreme field science are possible with circularly polarized high peak power ultrashort pulses. Commonly used quarter wave plates are not applicable here, while multi-mirror schemes are very complicated. We showed that the simple PET film $\approx$20 $\mu$m thick can be used to control the polarization state of the high peak power beam and achieve ellipticity of $\approx$0.8 with negligible nonlinear phase distortion. The film can withstand $10^3$ shots at intensity of $I = 3 \cdot 10^{12}$ W/cm$^2$ without visible damage. Thus, for a PW laser system and beam diameter of 20 cm the PET film can be used for quite a long time. We proved this experimentally using 1 TW femtosecond Ti:Sa laser measuring the angular distribution of the second harmonic from the plasma channel created in an undercritical gas plume.