Ultrafast confocal fluorescence microscopy beyond the fluorescence lifetime limit

Laser-scanning confocal fluorescence microscopy is an indispensable tool for biomedical research by virtue of its high spatial resolution. Its temporal resolution is equally important, but is still inadequate for many applications. Here we present a confocal fluorescence microscope that, for the first time to our knowledge, surpasses the highest possible frame rate constrained only by the fluorescence lifetime of fluorophores (typically a few to several nanoseconds). This microscope is enabled by integrating a broadband, spatially distributed, dual-frequency comb or spatial dual-comb and quadrature amplitude modulation for optimizing spectral efficiency into frequency-division multiplexing with single-pixel photodetection for signal integration. Specifically, we demonstrate confocal fluorescence microscopy at a record high frame rate of 16,000 frames/s. To show its broad biomedical utility, we use the microscope to demonstrate 3D volumetric confocal fluorescence microscopy of cellular dynamics at 104 volumes/s and confocal fluorescence imaging flow cytometry of hematological and microalgal cells at up to 2 m/s.