Fig. 2: Optothermal resonance scanning spectroscopy.

a Schematics of the setup for optothermal spectroscopy. PLC polarization controller, PD photodetector, PM power meter, DAQ data acquisition, WDM wavelength division multiplexer. b Calculated temperature change of a high-Q mode during the wavelength upscanning process. Inset: transmission of a high-Q mode in the 1550 nm wavelength band scanned by a thermal pump WGM in the 1440 nm wavelength band⁵⁰. c Transmission spectrum frames acquired by optothermal spectroscopy. Here, a nanofiber tip is repeatedly approaching and moving away from the microtoroid⁵⁷. Reprinted with permission from ref. ⁵⁷ [American Institute of Physics]