Theory of electromagnetic and ultrasonic nonlinear absorption in dielectric glasses

Nonlinear ultrasound and electromagnetic relaxation absorption in glasses at low temperature is evaluated. All consideration is based on the two-level system model. It is shown that in contrast to the linear case there are not two but three characteristic frequency intervals. Two of them reduce to the linear cases 1 and 1 when external-field amplitude decreases (is the frequency, is the relaxation time). The third interval vanishes in linear limit. In every frequency interval the relaxation of two-level systems is analyzed, and the dependence of absorbing power on frequency, temperature, and external-field amplitude is evaluated.