Nonstationary nonlinear effects in optical microspheres

Thermal nonlinearity can produce oscillatory instability in optical microspheres. We analyze theoretically the conditions of observations of this regime and demonstrate it experimentally. The observed curves are well compared with results of numerical modelling. In pure fused silica with low absorption thermal oscillations are suppressed due to concurrency with Kerr nonlinearity. We also describe for the first time experimentally observed slow and irreversible thermooptical processes in microspheres.