Synchronization-free light sheet microscopy based on a 2D phase mask

High-speed 3D microscopic imaging methods have led to numerous biological discoveries. In this Letter, we present a sync-free light sheet microscope (LSM) based on a static phase mask that eliminates the need for coupling the detection plane, thereby enabling high-speed volumetric imaging that is only limited by the speed of cameras, e.g., ∼1000 cross sections/s. In the sync-free design, the emission signals are first guided to the back of a galvanometric mirror, which laterally scans the emissions across a 2D phase mask, converting it to axial scanning that automatically compensates the focal shifts in the detection optics. Parametric models are developed to guide the phase mask design as well as to relate the axial scanning depth and magnification to design parameters. To quickly evaluate the different mask designs, a liquid-crystal-based spatial light modulator (LC-SLM) is used in the system. In the experiments, we scanned pollen and tissue samples via both the 2D phase mask and a piezoelectric objective scanner. The results show that the new method can generate clear images with comparable quality throughout the scanning range. The overall efficiency of the LSM is ∼10%. It is worthwhile to note that the efficiency will be significantly improved by replacing the LC-SLM with a custom-made lens. The new method realizes a compact LSM for high-speed 3D imaging that may find important applications in in vivo biological imaging.