ON NONLINEAR-OPTICAL PROPERTIES OF SEMICONDUCTOR HETEROSTRUCTURES

It is shown that Floquet states follow adiabatic changes of laser puls es unless quasi-energies meet avoided crossings. At these avoided cros sings quantum systems jump from one Floquet state to another with sign ificant probability rates. These transitions, which we call the optica l Landau-Zener transitions, lead to modifications of the power spectru m of scattered radiation, increasing its background significantly. It is shown, on the basis of numerical model calculations, that there is a connection between the chaotic behaviour of scattered radiation, mea sured by the autocorrelation function of its power spectrum, and the s pectrum of quasi-energies for different light intensities. Namely, it appears that the more avoided crossings a quantum system passes during the switching on and off of the laser pulse the more chaotic is the p ower spectrum of scattered radiation. Resonant scattering of electrons by quantum wells is also considered.