The impact of compressor gratings and transport optics imperfections on the power contrast ratio (PCR) is considered analytically, taking into account diffraction and all dispersion orders. All types of imperfections, including surface roughness, reflectivity fluctuations and surface dirt/damage/obscuration as well as the roughness and obscuration on the optics used to write holographic gratings are allowed for. For the same roughness and obscuration, the contribution to the PCR of the latter is significantly greater than the contribution of the gratings. Comparison of the PCR caused by obscuration and by roughness showed that at short times the latter prevails, whereas at long times the obscuration is dominant. The radiation scattered by the second and third gratings arrives at the target before the main pulse in the form of a vertical strip near the beam axis. Then this strip moves uniformly towards the axis, reaching it simultaneously with the main pulse.
