  Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool for
quantitative fluorescence imaging because fluorescence lifetime is independent
of concentration of fluorescent molecules or excitation/detection efficiency
and is robust to photobleaching. However, since FLIM is based on point-to-point
measurements, mechanical scanning of a focal spot is needed for forming an
image, which hampers rapid imaging. In this article, we demonstrate scan-less
full-field FLIM based on a one-to-one correspondence between two-dimensional
(2D) image pixels and frequency-multiplexed RF signals. A vast number of
dual-optical-comb beats between dual optical frequency combs is effectively
adopted for 2D spectral mapping and high-density frequency multiplexing in
radio-frequency region. Bimodal images of fluorescence amplitude and lifetime
are obtained with high quantitativeness from amplitude and phase spectra of
fluorescence RF comb modes without the need for mechanical scanning. The
proposed method will be useful for rapid quantitative fluorescence imaging in
life science.
