Polarization behaviour and damage thresholds of long-period diffractive samplers

Recently (Ciofini et al 2003 J. Opt. A: Pure Appl. Opt. 5 186-91) we introduced the use of very low-frequency diffraction gratings to extract good-quality, low-power copies of a high-power laser beam. We proved that beam propagation parameters are consistently measured for low-power sampled beams. In this paper we show that this type of optical sampler does not introduce any sizable perturbation in the field polarization. Moreover, it is shown that the polarization state is substantially preserved in the sampled beams, with the result that it can be conveniently measured at a low power level. Finally, our experimental tests prove that the limited number of surface steps used to sample the beam do not significantly reduce the CW laser-induced damage threshold (LIDT). Our tests show that the CW LIDT of this component differs by less than 10% from that of a flat mirror with the same multilayer coating. This confirms the ruggedness of these samplers and their suitability for use in high-power laser beam measurements.