Polarized photoacoustic microscopy for vectorial-absorption-based anisotropy detection.

We proposed polarized photoacoustic microscopy (PPAM) for quantitative detection of a target's microscopic anisotropy based on the vectorial optical absorption by applying four linearly polarized laser beams as excitation sources. Compared to conventional photoacoustic microscopy that treats targets as isotropic absorbers, PPAM allows us to quantitatively detect the target's anisotropic features beyond optical absorption with a newly proposed parameter valued between 0 and 1. The feasibility of the method was validated by dichroic phantoms. The dichroic compound eyes of mantis shrimps were imaged in situ to demonstrate the method's capability for quantitative three-dimensional biological imaging. The PPAM method provides an effective and straightforward strategy for tissue polarimetry, prefiguring great potential for biological imaging and material inspection.