In vivo fast variable focus photoacoustic microscopy using an electrically tunable lens

Fast focusing scan over a large depth range is challenging in photoacoustic microscopic imaging. In this paper, a fast variable focus photoacoustic microscopy (VF-PAM) with a large range of imaging depth was presented by using an electrically tunable lens (ETL). The ETL controlled the divergence angle of the laser beam for fast and continuous focus-shifting in depth direction with the shifting time of 15 ms, and 2.82 mm focus-shifting range with a 1 µm shifting accuracy was achieved by combining the ETL with a 0.3 NA plan microscope objective lens. Carbon fibers imaging verified the depth imaging ability of the system, in vivo microvasculature of mouse ear and brain tissues of the mouse imaging further demonstrated the focusing scan ability in biomedical application. The fast VF-PAM system allows substantial shortening of the focus-shifting time, which will be more conducive to studying living biological tissue, and will promote the development of in vivo noninvasive PA depth imaging without mechanical scan.