  We demonstrate a thermal infrared (IR) detector based on an
ultra-high-quality-factor (Q) whispering-gallery-mode (WGM) microtoroidal
silica resonator, and investigate its performance to detect IR radiation at 10
micron wavelength. The bandwidth and the sensitivity of the detector are
dependent on the power of a probe laser and the detuning between the probe
laser and the resonance frequency of the resonator. The microtoroid IR sensor
achieved a noise-equivalent-power (NEP) of 7.46 nW, corresponding to IR
intensity of 0.095 mW/cm^2
