Large-DOF ultraviolet photoacoustic microscopy using liquid crystal-based diffractive optical element

As strong optical absorption of DNA/RNA to Ultraviolet (UV) light, UV-Photoacoustic Microscopy (UV-PAM) can highlight the cell nuclei of tissues at outstanding imaging contrast without introduction of exogenous contrast agents. However, a short Depth of Focus (DOF) in the traditional UV-PAM results in out-of-focus imaging artifacts when imaging unprocessed tissue specimens that are usually characterized by uneven surface topology, which possibly degrades the histopathological examinations. We propose the wavefront engineering of UV photoacoustic illumination using a liquid crystal-based diffractive optical element (LC-DOE) to precisely manipulate the phases of the incident UV beam, enabling UV-PAM to produce an enlarged DOF (~250 μm) while maintaining subcellular lateral resolution (~1.02 μm) within the extended depth range. The system demonstrates high-resolution volumetric image of a phantoms made from many tungsten filaments. We anticipate that, with the liquid crystal-based diffractive optical element, the UV-PAM accommodates to image the unprocessed tissue samples, and thus potentially assists for non-destructive and label-free histopathology assessments of various disorders.