Measurements of the total energy reflected from crystalline and amorphous silicon illuminated by a femtosecond laser pulse are reported, for wavelengths of 0.62 and 0.31 {μ}m. The results are interpreted by use of a highly nonlinear regime of light propagation in the dense plasma of electrons and holes (e-h). Densities higher than 10²² cm^-3 are reached. We demonstrate that free-carrier absorption is dominated by e-h collisions.
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Hulín et al. (1984) studied this question.