Figure 3. Thermal and Kerr non-linearities measured by CRUS.

The graphs show the centre frequency of the probed WGM (red dots, interpolation in blue) as extracted from CRUS spectra for: (a) thermal oscillations induced by the turn-on of a pump beam modulated at 300 kHz. The oscillations are superimposed on a drifting central frequency, which reflects the gradual increase in the microtoroid's average temperature. The spectra were captured every 200 ns. The inset shows the phase lag between the induced oscillations and the pump (black curve). (b) The relaxation of the resonant frequency following the turn-off of the pump. The cooling of the cavity can be separated into a slow decay (corresponding to a cutoff frequency of Ω₁=5.1 kHz) and a fast decay (cutoff frequency Ω₂=210 kHz). (c) Kerr oscillations induced by the turn-on of a pump beam modulated at 5.5 MHz. The spectra were captured every 37 ns. The instantaneous response of the Kerr effect is exhibited by nearly zero phase shift with respect to the pump (inset).