Light turn-on transient of a whispering gallery mode resonance spectrum in different gas atmospheres.

We examine the resonance spectrum change after turning on the light to feed the fiber taper evanescently coupled to a silica whispering gallery mode (WGM) resonator surrounded by different gases at different pressures. The resonance shifted to a longer wavelength, indicating a temperature rise, before reaching a steady state. The increment was proportional to the power of the light and approximately reciprocally proportional to the thermal conductivity of the surrounding gas, whereas the rate of the shift was approximately proportional to the thermal conductivity. The temperature rise, caused by absorption of intense WGM in silica, was significant even when the wavelength scan range contained only a few tall resonance peaks. We then estimated the power of heat generation and the mean power of WGM during the wavelength scan.