CC BY
15LMI-I-2
Ultrafast oscillatory dynamics of free carriers in semiconductors driven by intense ultrashort laser pulses: a basis of novel
technologies
Vitaly Gruzdev
Department of Physics and Astronomy, University of New Mexico, 210 Yale Blvd. NE, Albuquerque, NM, 87106, USA
E-mail: [email protected]
A broad range of ultrafast laser interactions with semiconductors receive reasonable interpretation in terms of frequent electron-phonon collisions with characteristic collision time about 1 femtosecond. Those interpretations support a broad range of experimental data on laser-induced ablation, ultrafast melting, and characterization of transient optical response by pump-probe methods [1, 2]. However, reasonable interpretations of the recently reported generation of very high-order harmonics [3, 4] and electric charge [5, 6] in dielectrics and semiconductors assume minor perturbation of the laser-driven electron dynamics by electron-particle collisions. The latter means the electron-phonon collision time must be comparable to pulse width that is typically about 100 femtoseconds. The contradiction between the two assumptions is removed by considering energy dependence of electron-phonon collision time. Quasi-resonant promotion of valence-band electrons to the very bottom part of a conduction band results in the magnitudes of electron-particle collision time as large as hundreds of femtosecond. In this case, the laser-generated free electrons perform laser-driven oscillations with a minor perturbation from the low-rate collisions. This type of laser-driven free-carrier dynamics may serve as a fundamental mechanism of novel physical effects. Among them, we consider ultrafast conversion of multi-cycle laser pulses into femtosecond pulses of electric current and amplification of low-power probe laser pulses by the oscillating free-carrier plasma. In contrary to the pioneering results of Refs. [5, 6], the ultrafast light-to-current conversion by the laser-driven free-carrier oscillations is feasible for laser pulses carrying as many as 15 to 20 cycles, i. e., at pulse width of about 100 fs. We discuss parametric scaling of the photocurrent and its applications in sub-PHz optoelectronics, generation of ultrashort pulse of strong magnetic fields, and THz pulses. The oscillating free carriers may also experience induced inverse bremsstrahlung effect due to scattering by ions of a crystal lattice. Under some conditions specified by our theoretical calculations, that scattering results in domination of light amplification over absorption. This process may serve as a basis for novel approaches of parametric amplification of ultrashort laser pulses that may be especially efficient for mid-infrared spectrum range.
This work is supported by Research Technology & Laboratory Directorate / Basic Research Office of the US Department of Defense via Newton Award for Transformative Ideas during the COVID-19 Pandemic No. HQ00342010028 and the Air Force Office of Scientific Research under award number FA9550-15-1-0254.
