Perturbation of a resonator by a thermal lens formed in an internal element

A report is given of an investigation of the perturbation of a resonator by a weakly absorbing internal element which exhibits a temperature dependence of the refractive index. A thermal lens, which is induced in such an element as a result of the absorption of some of the internal radiation, gives rise to a hysteresis in the dependence of the stability region of the resonator and, consequently, of the output power on the pump power. The influence of such a thermal lens in a weakly absorbing element on the composition of the transverse output modes is investigated theoretically and experimentally.