Super-resolution PA imaging has been achieved by different groups including us. Depending on the imaging depth, the spatial resolution of PAT was long limited by acoustic diffraction in the optical diffusive regime or by optical diffraction in the optical ballistic regime. We have been working on breaking the spatial resolution limits by various nonlinear photoacoustic effects, including photoacoustic absorption bleaching, photothermal effect, and reversible photoacoustic switching. A lateral resolution of 80 nm has been achieved with inherent optical sectioning, which is not available in traditional photoacoustic imaging.
