Absorption of powerful light by free electrons in crystals: intraband electron–phonon Rabi oscillations

The absorption of high-power visible or near-IR laser radiation by free electrons is calculated using the modified resonance approximation. The probabilities $W_{\operatorname{exc}}$ of intraband transitions at which the electron energy changes by $\hbar(\omega\pm\omega_{l})$, where $\omega$ is the frequency of light and $\omega_l$ is the frequency of longitudinal optical phonons involved in the process, are determined. It is shown that specific electron–phonon Rabi oscillations at a frequency of $\Omega_{R}$ may take place, and that the light is absorbed only up to the moment of time at which the first maximum $\tau_1$ on the dependence $W_{\operatorname{exc}}(t)$ is reached, where t is the time elapsed from the beginning of the laser pulse. It is shown that, in the case of prebreakdown light intensities, processes of high orders in the field of the light wave affect substantially $W_{\operatorname{exc}}$, $\tau_1$, and $\Omega_{R}$.