  Nanosecond temporal resolution enables new methods for wide-field imaging
like time-of-flight, gated detection, and fluorescence lifetime. The optical
efficiency of existing approaches, however, presents challenges for low-light
applications common to fluorescence microscopy and single-molecule imaging. We
demonstrate the use of Pockels cells for wide-field image gating with
nanosecond temporal resolution and high photon collection efficiency. Two
temporal frames are obtained by combining a Pockels cell with a pair of
polarizing beam-splitters. We show multi-label fluorescence lifetime imaging
microscopy (FLIM), single-molecule lifetime spectroscopy, and fast single-frame
FLIM at the camera frame rate with $10^3 - 10^5$ times higher throughput than
single photon counting. Finally, we demonstrate a space-to-time image
multiplexer using a re-imaging optical cavity with a tilted mirror to extend
the Pockels cell technique to multiple temporal frames. These methods enable
nanosecond imaging with standard optical systems and sensors, opening a new
temporal dimension for low-light microscopy.
