Shear‐Force Photoacoustic Microscopy: Toward Super‐Resolution Near‐Field Imaging

Abstract Optical‐resolution photoacoustic microscopy (OR‐PAM) enables both high‐resolution and high‐contrast imaging of optical chromophores ranging from biological tissues to inorganic samples. The lateral spatial resolution of OR‐PAM depends on its optical configuration and is primarily determined by the numerical aperture of the objective lens. This study demonstrates a novel, lens‐free, shear‐force photoacoustic microscopy system using a tapered fiber, serving as a proof‐of‐concept toward the implementation of super‐resolution, near‐field scanning photoacoustic microscopy. An uncoated tapered fiber is attached to a quartz tuning fork, thereby maintaining the near‐field distance between the fiber and sample surface via a shear‐force detection mechanism. Light‐field simulation confirms an evanescent wave at the end of the uncoated, tapered fiber. Based on the photoacoustic simulation and 2D photoacoustic scanning experimental results, targets are imaged with high‐lateral resolutions of the order of 1.0 ± 0.3 µm. These results demonstrate the existence of near‐field photoacoustic signals and the potential for future development of super‐resolution, near‐field, scanning photoacoustic microscopy.