  Current optoacoustic microscopy configurations often have narrow focal ranges
that limit their use for fast volumetric imaging applications. Here, the focal
range of optoacoustic microscopes is extended by matching the elongated optical
illumination profile of a Bessel beam with the pencil beam acoustic sensitivity
profile of a broadband axicon detector. An inverted optoacoustic microscope was
developed with interchangeable optical illumination and acoustic detection
units to assess the imaging depths and resolutions retained with several
combinations of illumination and detection profiles. Matching Bessel
illumination with axicon detection extends the depth-of-focus 17-fold over
traditional configurations. Imaging a tilted mouse ear with the matched
Bessel-axicon configuration revealed vasculature over an imaging depth
exceeding 4.2 mm with optical resolution, while affording a 6-fold increase in
imaging volume over the same scanning duration compared to configurations
employing standard Gaussian illumination, demonstrating this approach's promise
for increasing applications for optoacoustic microscopy in preclinical
research.
