Spatial-frequency-extended single-pixel microscopic imaging via frequency-division multiplexing

The integration of single-pixel imaging (SPI) with frequency-division multiplexing (FDM) offers a powerful approach for biomorphological analysis. Among reported techniques, acousto-optic deflectors (AOD) generate frequency-shifted beams at distinct angles for heterodyne interference with the expanded reference beam at the objective lens. Misalignment between the AOD aperture and the objective aperture induces numerical aperture (NA) mismatch, causing AOD-generated spots to deviate from the diffraction limit and limiting spatial resolution due to post-focusing spot size. We propose a "pre-magnification and post-sampling" imaging method that enhances resolution while maintaining fixed sampling frequency constraints. By integrating the target into the interferometer and employing a lens assembly with tunable focal length ratios, we achieved dynamically adjustable spatial resolution. Experimental results demonstrate a resolution tuning range of 4.5 µm to 13 µm under the spot size of 10.8 µm. Utilizing a one-dimensional beam array composed of 40 spots, we constructed patterns across a 720 x 112.5 µm² area with 4.5 µm spatial resolution. This approach effectively decouples resolution enhancement from sampling frequency limitations.