High-speed varifocal optical-resolution photoacoustic microscope to achieve large depth of field based on a tunable acoustic gradient lens

We developed an optical-resolution photoacoustic microscope (OR-PAM) capable of changing focal plane with high-speed by using a tunable acoustic gradient (TAG) lens. In our system, a TAG lens is designed to continuously changing the focal plane of OR-PAM by modulating its refractive power with fast-changing ultrasonic standing wave. The raster-scanning of the microscope and laser pulses are synchronized to the same phase of the driving signal of TAG lens. By selecting the synchronized phase, arbitrary focal plane can be chosen in a range of about 1 millimeter in 1.4 microseconds in our system. A phantom composed by tungsten wires is used to verified the varifocal capability of the system. In-vivo study was carried out, to further demonstrate the large depth-of-field (DoF) achieved by our method without any moving part.