Ultrafast modification of band structure of wide-band-gap solids by ultrashort pulses of laser-driven electron oscillations

Abstract

The electric field of high-intensity ultrashort laser pulses substantially perturbs electron subsystem of a crystal and affects its band structure. Laser-driven oscillations of electrons and holes are frequently referred to as a major mechanism of the perturbation in dielectrics and semiconductors. New physical effects arise when the band structure is modified by an ultrashort pulse of the oscillations driven by a few-cycle laser pulse. Assuming the laser-pulse envelope varies slowly compared to the carrier frequency, we derive analytical relations for the laser-modified band structure by utilizing the Keldysh cycle-averaged non-perturbative approach under the approximation of constant effective mass. Formation of indirect-gap transient bands, suppression of the nonlinear absorption on the leading edge of a laser pulse, and cycle-averaged photo-current generation driven by the pulse envelope are predicted. Analytical scaling with six laser and material parameters is obtained. The reported results establish the limits of validity of the Keldysh photoionization model and advance understanding of the fundamental effects involved in high-intensity ultrafast laser-solid interactions.

Ultrafast Laser Material Damage Simulation—A New Look at an Old Problem

“…Third, the cycle-averaged approach for modeling of the photoionization assumes slow variations of pulse-envelope compared to field oscillations at the center frequency of laser-pulse spectrum [51,77]. With reduction of pulse duration towards few optical cycle, this requirement may be violated, and some corrections to the Keldysh-type model are required [77,78].…”

Laser induced distortion of band structure in solids: an analytic model

“…For narrow-bandgap semiconductor crystals, the optical resonance corresponds to the far infrared regime, which means a time scale which is at least a factor of ten longer than the optical period of the applied laser field. Additionally, since we assumed monochromatic excitation, sub-cycle effects play no role, similarly to [17]. The solution of the Schödinger equation is now modified as…”

“…To calculate statistical entropy measure or the Fisher-Shannon information [16] of this kind of potentials is also an interesting question. For recent results based on Keldysh cycle-averaged nonperturbative approach, see [17].…”

Optical Bloch modeling of few-cycle laser-induced electron dynamics in dielectrics

“…On the other hand, kinetic-type descriptions have been developed, accounting for all main collisional processes [38][39][40]. The laser pulse intensity-induced evolution of the band curvature is considered to be responsible for the material breakdown in [32,41,42]. But they generally do not account for the band structure beyond a single parabolic band and are currently computationally too expensive for their coupling to a Maxwell solver.…”