Differential-excitation photoacoustic microscopy beyond the optical diffraction limit

This simulation study introduces a differential-excitation strategy for frequency-domain photoacoustic microscopy, capable of achieving optical sub-diffraction-limited lateral resolution. By spatially overlapping Gaussian and donut beams with π radians phase–shifted modulation, the effective excitation region is confined, reducing the normalized full width at half maximum value from 1.177 to 0.828 units. This effect corresponds to a ~1.42-fold lateral resolution enhancement compared with conventional focused Gaussian beam excitation. Optimal performance is achieved at an optical power ratio of 1.16, balancing side-lobe suppression and excitation confinement. The proposed approach offers a cost-efficient path to sub-diffraction photoacoustic microscopy, with potential impact in high-resolution biomedical imaging of subcellular and microvascular structures.