Flexible depth-of-focus, depth-invariant resolution photoacoustic microscopy with Airy beam

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Abstract
Optical-resolution photoacoustic microscopy (OR-PAM), as an emerging and hybrid technique, enables label-free and in vivo anatomical as well as functional imaging of the microvasculature, lipids, and melanin in biological tissue with deep penetration.1 – 5 OR-PAM inherently possesses the depth-resolving capacity, utilizing the time-of-flight data captured in each photoacoustic signal during A-scan excitation. This unique feature allows for volumetric imaging with only two-dimensional (2D) raster scanning. To achieve optical-diffraction-limited lateral resolution, a tightly focused Gaussian beam is selected using an optical objective in a standard OR-PAM system.2 – 7 Nevertheless, the diffraction limit causes the commonly used Gaussian beam to rapidly diverge along its propagation path, resulting in a notably brief depth of focus (DOF) for exciting photoacoustic signals. This restricted DOF prevents the consistent revelation of volumetric images with uniform lateral resolution across varying depths, thus hindering the accurate acquisition of anatomical, functional, and metabolic information concerning biological systems.

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