Differential Gain of THz Radiation in Crystalline Quartz in the Field of Pump Wave

We theoretically considered the possibility to exploit nonlinear Fabry–Pérot interferometers to differential gain of terahertz radiation in the field of a pump wave of the same frequency. It is shown that in a mirrorless nonlinear Fabry–Pérot interferometer, that consists of a crystalline quartz plate and which reflection is determined by Fresnel reflectivity only, the regime of maximal differential gain of radiation with central frequency at 1 THz can be observed at the plate thickness of near 1 mm and radiation intensity of 108 W cm–2 order.