Fig. 2: Qualitative and quantitative identifications of the intracavity losses.

a Normalized transmission of different input power with the same scan speed 792 MHz/s, showcasing the absorption-based thermal broadening. b Linear fitting of the triangle’s full width at half maximum (FWHM) as a function of input power P_in, with a fitted slope dΔf/dP_in of 7.01 MHz/mW. The vertical error bars give standard deviations in repeated measurements. c Measured Q_abs in 10 individual samples. d Atomic force microscope (AFM) image shows a root-mean-square (RMS) roughness of 11.2 nm, within a surface inhomogeneity coefficient (B) of 7.84 nm. e Calculated Q_sca, here the red dot illustrates the experimental case. f Measured Q_sca of 10 individual samples. g Electrical field distribution of a WGM microcavity, with diameter of 0.1 mm and a 1 nm thick water layer. h Calculated Q_cont versus thickness of water layer, in microcavities with diverse diameters. i Q_cont of 10 individual samples, which are achieved from the measured results 1/Q_cont = 1/Q₀-1/Q_abs-1/Q_sca-1/Q_rad.