Deformable mirror-based photoacoustic remote sensing (PARS) microscopy for depth scanning.

Optically shifting the focal plane to allow depth scanning of delicate biological structures and processes in their natural environment offers an appealing alternative to conventional mechanical scanning. Our technique uses a deformable mirror-based photoacoustic remote sensing microscopy (PARS) with a focus shifting of Δz ∼ 240 µm. We achieve this by integrating a deformable mirror that functions as a varifocal mirror for axial scanning. First, the system's focal shift capability was demonstrated with USAF resolution targets and carbon fiber phantoms, followed by in-vivo visualizations of blood vessels in chicken embryo chorioallantoic membrane (CAM). This work represents an initial step toward developing a non-contact, label-free, and aberration-free PARS imaging system with axial scanning capability.