Spin-dependent terahertz nonlinearities at inter-valence-band absorption in p-Ge

Far-infrared absorption and photon drag effect have been investigated in p-type germanium as a function of intensity of a high-power pulsed far-infrared molecular laser. Optical transmission shows saturation independent of the state of polarization of the radiation whereas in the photon drag effect a pronounced linear–circular dichroism occurs. Linear–circular dichroism is caused by spin-selective excitations as a result of selection rules and, equally important, multi-photon transitions with a rate comparable to one-photon absorption