Phase-modulated rapid-scanning fluorescence-detected two-dimensional electronic spectroscopy

In this work, we present a rapid scanning approach to fluorescence-detected two-dimensional electronic spectroscopy (FD-2DES). Our approach combines phase modulation with digital lock-in detection. Using phase-modulation each of the four pulses used to excite the sample is tagged with a specific radio-frequency. The resulting fluorescence signal is thus modulated at different linear combinations of these frequencies. Digital lock-in detection is used to retrieve complex linear and non-linear spectroscopic signals in a single measurement. The approach allows simultaneous tracking of interferometric time delays, correction of spectral phase distortions, and also enables accurate phasing of the data. We report the simultaneously acquired linear fluorescence excitation spectrum, rephasing, non-rephasing, and absorptive FD-2DES spectra of the laser dye IR-140 in DMSO.