Fig. 1. (a) Experimental setup. The pulsed 532 nm laser is circularly polarized, with a repetition rate of 5 MHz. DM: dichroic mirror; APD: avalanche photodiode. (b) The fluorescence emission of a single NV center with different laser intensities. The blue line is the fitting with Eq. (1). (c) Simulated point spread function and the spatial frequency distribution of the confocal microscopy with different powers. (d) The normalized spatial frequency with the excitation power of 0.06 and 1.2 mW. For comparison, we also show the results with a traditional saturating [b=0 in Eq. (1)]. The insert is the ratio of the high spatial frequency signal with different excitation laser powers.

Fig. 2. (a) Sequences of the laser’s modulation and fluorescence detection. (b) The images of a single NV center. The confocal microscopy images of Ilow and Ihigh are recorded to calculate the final image Ir. Cross-section profiles corresponding to the dashed lines in the images of single NV center are shown on the upsides. (c) The spatial resolution of ASAX microscopy with different γ. The error bars are the deviation of the results. The insets are images of a single NV center with γ=0, 0.6, and 1.0. The scale bars are 500 nm in length. (d) The lateral cross-section profiles of ASAX images with γ=0, 0.6, and 1.0. (e) The spatial frequency distribution of ASAX images with different γ. (f) The SNR of the Ir as a function of γ.

Fig. 3. (a), (d) Multiple NV centers imaged with the confocal microscopies. (b), (e) Multiple NV centers imaged with ASAX microscopies. The scale bars are 1 μm in length. (c) and (f) are the cross-section profiles indicated by the arrows.