Calculated transmission of the optical pulse of a wavelength of 630 nm, for the average absorbed dose of 0.8 eV/atom, in the layer thickness of 38 nm (at the time instance of 400 fs; red solid line). FEL photon energy was 47.4 eV, pulse duration was 52.5 fs (FWHM, magenta dashed line). It is compared to the experimental data (open black squares with errorbars). Intervals (i)–(iii) denote different stages of graphitization. The figure is reproduced from reference [10].