Features of the laser ionization of crystalline broad-band insulators

Based on the procedure proposed by L. V. Keldysh, the ionization rate is calculated for a two-band cosine model of the energy structure of a crystal corresponding to the strong-coupling approximation. The main difference from earlier papers is that it directly takes into account the contribution of Bragg reflections of electrons at the boundaries of the Brillouin zone due to the specific choice of the dispersion relation. As a result of the calculation, a singularity is obtained on the intensity dependence of the ionization rate, which occurs at intensities around 10 TW/cm2 for broad-band insulator crystals. The meaning and physical causes of this singularity are analyzed, as well as the degree to which it is affected by the mathematical procedure used for the calculation.