Modification of band structure of wide-band-gap crystals by non-monochromatic electron/hole oscillations driven by high-intensity ultrashort pulses*

Electric field of high-intensity ultrashort laser pulses distorts band structure of crystals. In wide-band-gap crystals, the fastest distortions are attributed to coherent laser-driven electron oscillations frequently analyzed under a monochromatic approximation. We report a theoretical study of non-perturbative band-structure modification by ponderomotive energy of non-monochromatic laser-driven electron/hole oscillations treated by a quasi-classical approximation. A slowly-varying pulse envelope is assumed, but variations of field amplitude within each individual cycle are taken into account. Laser-perturbed time-dependent energy-momentum relations are averaged over a single laser cycle and asymptotically expanded using a small parameter (ratio of cycle duration to pulse width) to obtain analytical formulae. A shift of the laser-modified energy bands with respect to each other along a quasi-momentum direction parallel to laser-pulse polarization and asymmetric (with respect to laser-pulse peak) time evolution of effective band gap are predicted. Those effects substantially affect nonlinear absorption and are controlled by pulse phase, pulse width, peak intensity, and carrier wavelength.