  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.
