Polarization state control for high-peak-power applications

The use of circularly polarized high-peak-power ultrashort pulses has various applications in extreme field science. Commonly used quarter-wave plates are unsuitable here, while multi-mirror schemes are technically complicated. We have demonstrated that simple PET film, 20.5µ<i>m</i> thick, can be used to manipulate the polarization state of the high-peak-power beam and achieve ellipticity of up to 0.8 with negligible nonlinear phase distortion. Furthermore, the film can withstand 10³ shots at an intensity of <i>I</i>=3⋅10¹²<i>W</i>/<i>c</i><i>m</i>² without sustaining visible damage. Thus, PET film is suitable for long-term use in a PW laser system, with a 20 cm beam diameter. We confirmed this experimentally by measuring the angular distribution of the second harmonic from the plasma channel created in an undercritical gas plume, with a 1 TW femtosecond Ti:Sa laser.