Threshold-free optical bistability due to giant nonlinearity of resonance absorption in crystals containing FA centers

An analysis is made of a polarization optical bistability in crystals containing F_A centers and placed in a resonator. The bistability is due to the possibility of amplification of fluctuations of the polarization of radiation in such crystals and in practice has no threshold in respect of the radiation intensity. An analysis is made of the ranges of values of the parameters of a doped crystal and of a resonator in which this bistability can be observed. The analysis is carried out for ring and Fabry–Perot resonators.