Harmonics generation in quantum-size structures in a strong electromagnetic field

Abstract

Harmonics generation in a system of tunneling-coupled quantum wells is investigated by solving numerically the nonstationary Schrodinger equation, without using perturbation theory, in an external electromagnetic field. The time-dependence of the dipole moment is calculated and a method is proposed for calculating the radiation intensity at a fixed frequency. For systems containing three equidistant energy levels, it is shown that the effect of the field on the energy spectrum becomes substantial at intensities of several hundreds V/cm; the system falls out of resonance. The field-dependence of the second harmonic amplitude becomes nonquadratic, in contrast to the dependence predicted by perturbation theory, and the system passes into a stable level. In the quasienergy-crossing regime, it is shown that even-harmonics generation is possible in a symmetric system in a strong field. The amplitude of the harmonics is largely determined by the initial state of the system. It is possible to have a situation where the amplitude of the generated harmonic can even be greater than in structures with a resonance configuration of energy levels (three equidistant levels for the second harmonic).