Dispersion compensation for acousto-optic scanning two-photon microscopy

Abstract

In laser scanning microscopy, acousto-optic (AO) deflection provides a means to quickly position a laser beam to random locations. Compared to conventional scanning using galvanometer-driven mirrors, this approach increases the frame rate and signal-to-noise ratio, and reduces time spent illuminating sites of no interest. However, AO scanning has not yet been applied to multi-photon microscopy, primarily, because the femtosecond laser pulses employed are subject to significant amounts of both temporal and spatial dispersion upon propagation through common AO materials. Temporal dispersion of ultrashort pulses - also known as group velocity dispersion (GVD) - is commonly compensated by the inclusion of a pre-chirper. However, because of the large GVD of AO materials, commonly used pre-chirper designs entail a rather large footprint (> 2 meters). Spatial dispersion of the scanned beam - arising from AO deflection being a wavelength-dependent diffraction process - limits the achievable spatial resolution. To address these problems, we developed: 1) a novel four-pass double-decker pre-chirper geometry that reduces the assembly's footprint by another factor of two relative to current designs, and 2) a single diffraction grating scheme for significantly reducing spatial dispersion. The presented findings enable the construction of an acousto-optic two-photon microscope (AO-TPM).© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.