Converting lateral scanning into axial focusing to speed up 3D microscopy
In optical microscopy, the slow axial scanning rate of the objective or the sample has traditionally limited the speed of 3D volumetric imaging. Recently, by conjugating either a movable-mirror to the image plane or an electrotuneable lens (ETL) to the back-focal plane respectively, rapid axial scanning has been achieved. However, mechanical actuation of a mirror limits axial scanning rate (usually only 10-100 Hz for piezoelectric or voice coil based actuators), while ETLs introduce spherical and higher order aberrations, thereby preventing high-resolution imaging. Here, we introduce a novel optical design that can transform a lateral-scan motion into a spherical-aberration-free, high-resolution, rapid axial scan. Using a galvanometric mirror, we scan a laser beam laterally in a remote-focusing arm, which is then back-reflected from different heights of a mirror in image space. We characterize the optical performance of this remote focusing technique and use it to accelerate axially swept light-sheet microscopy (ASLM) by one order of magnitude, allowing the quantification of rapid vesicular dynamics in 3D.