The extreme temperature sensitivity of whispering-gallery-mode (WGM) microresonators holds great promise as a detection strategy for single-particle photothermal microscopy and spectroscopy. The detection limit is currently partially constrained by frequency noise from the laser used to probe the cavity resonance wavelength. We present a measurement technique capable of simultaneously detecting backscattered and transmitted light from a wavelengthlocked optical microresonator, with laser intensity noise and frequency noise partitioned into the two independent detection channels. Photothermal mapping of single absorbing nano-objects demonstrates that both methods are capable of high signal/noise, exceeding 30,000:1 in the backscattering channel for a photothermally-induced microresonator resonance shift of 93 fm.
Kevin D. Heylman, Erik H. Horak, Kassandra A. Knapper, and Randall H. Goldsmith, "Photothermal microresonator absorption microscopy with backscatter detection," Proc. SPIE 9554, Nanoimaging and Nanospectroscopy III, 95540U (Presented at SPIE Nanoscience + Engineering: August 11, 2015; Published: 26 August 2015); https://doi.org/10.1117/12.2187240.
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