Spectrally-selective Time-resolved Emission through Fourier-filtering (STEF)

In this manuscript we demonstrate that directing the emitted photon stream from a fluorescent sample through a fixed path-length imbalanced Mach-Zehnder interferometer allows us to separate and resolve the dynamics of different emitters without the use of filtering optics. Our method, Spectrallyselective Time-resolved Emission through Fourier-filtering (STEF) takes advantage of a careful selection of interferometer position where one signal can be canceled (or enhanced) due to its unique spectral characteristics. STEF is straightforward to implement and provides a complementary approach to separate spectrally overlapped signals based on their coherence length and carrier frequency. We also discuss how one can implement STEF with an imperfect Mach-Zehnder interferometer, increasing the utility of this method, and demonstrate how Mach-Zehnder filtering can be used to image fluorophores in biologically relevant samples.