Fig. 1. Working principle of high-speed modes imaging. (a) Schematic of the experimental setup for high-speed modes imaging. A 1 kHz high-repetition frequency fs laser serves as the pump laser source, while a near-infrared laser acts as the probe source. The repetition frequency of the fs laser is utilized as the clock signal to drive the entire system to operate. (b) Under the excitation of a single fs pulse, the transmission spectra of the resonant modes in the microcavity exhibit a shift. Points 1, 2, and 3 correspond to the initial transmittance at the fixed probe wavelength, and the subsequent changes induced by free-carrier diffusion and nonradiative recombination effects, respectively. (c) Sudden change of the transmittance level signal at the probe wavelength affected by a single fs laser pulse in the oscilloscope. Points 1, 2, and 3 are consistent with those in (b).

Fig. 2. High-speed imaging of resonant modes in a quadrupole microcavity with radius of 50 μm. (a) SEM image of a quadrupole microcavity with radius of 50 μm. (b) Transmittance of the microcavity within the wavelength range of two adjacent FSRs and relative positions of the 10 resonant modes. (c) FSRs of the 10 resonant modes in panel (b); the minimum difference between these FSRs is only 4 pm. (d) High-speed imaging patterns of the 10 resonant modes and the corresponding numerical simulations of the optical field distribution. The scale bar is 12 μm.

Fig. 3. The resonant modes in the transmission spectra of a 50 μm quadrupole microcavity vary with different coupling gaps. (a) The corresponding transmission spectra and resonant modes when the coupling gap varies within the range of 100–140 nm. (b) The high-speed imaging patterns and corresponding numerical simulations of the newly generated resonant modes under different coupling gaps, as shown in the transmission spectra of (a). The scale bar is 12 μm.

Fig. 4. Imaging time required for resonant modes under different quadrupole microcavity radii. Comparison of imaging time required for high-speed modes imaging technique with different quadrupole microcavity radii and nanosecond laser imaging technique. The step size from left to right is 0.55, 0.9, 1.2, 1.4, and 2.4 μm, respectively.