Non-contact anisotropy detection based on polarized photoacoustic remote sensing microscopy

As a key and unique feature, anisotropy is the variability of material properties in different directions caused by molecular conformation and structural arrangement. The optical properties of anisotropic materials include birefringence and dichroism, and the characterization of these properties can be used to detect changes in the microstructure of materials. Conventional polarized optics imaging and photoacoustic imaging are based on scattering and contact measurements respectively, limiting many applications. Photoacoustic remote sensing (PARS) is an all-optical, non-contact photoacoustic measurement technique that provides specific light absorption contrast without coupling or labeling. However, PARS usually ignores tissue uptake anisotropy, which may result in missing some unique tissue properties and information. To obtain more dimensional information on targets, here we propose polarized photoacoustic remote sensing (P-PARS) microscopy. The system uses linearly polarized light in different directions as the excitation source and indicates the anisotropic optical absorption of the target by detecting changes in the reflected intensity of the interrogation light. It can simultaneously provide images of optical absorption contrast and the degree of anisotropy. Experimental results of testing materials and biological tissues demonstrated the feasibility and stability of the P-PARS. This method provides a new noncontact label-free strategy for anisotropy detection, prefiguring important potential for anisotropic material inspection and biological tissue imaging.