Ultrasensitive real-time measurement of dissipation and dispersion in a whispering-gallery mode microresonator.

We present the characterization of the recently developed cavity enhanced amplitude modulation laser absorption spectroscopy (CEAMLAS) technique to measure dissipation within the evanescent field of a whispering-gallery mode resonator, and demonstrate the parallel use of CEAMLAS and the Pound-Drever-Hall measurement techniques to provide both dissipation and dispersive real-time microresonator measurements. Using an atomic force microscope tip, we introduce a controlled perturbation to the evanescent field of the resonator. In this case, dissipative sensing allows up to 16.8 dB sensitivity improvement over dispersive measurements, providing the possibility for enhanced sensitivity in application such as biomolecule detection.