Behaviour of nonlinear liquid-crystal mirrors, made of a nonabsorbing cholesteric, in the cavity of an Nd:YAG laser operating in the cw regime and at a high pulse repetition frequency

Nonlinear bleaching of output mirrors, made of a nonabsorbing cholesteric, in an Nd:YAG laser was investigated. In the cw regime there was no difference between the output powers of lasers with dielectric and cholesteric mirrors. In the pulse-periodic regime (pulse duration 500 ns, repetition frequency 4.5 kHz) the lasing disappeared after 0.5 — 5.0 min because of a strong reduction in the reflection coefficient of the output mirror bleached by laser pulses. The observed effect was independent of the average power density and this made it possible to attribute it to an increase in the pitch of the cholesteric helix in the optical wave field.