Half-broadband two-dimensional electronic spectroscopy with active noise reduction.

Two-dimensional electronic spectroscopy (2DES) provides detailed insight into coherent ultrafast molecular dynamics in the condensed phase. Here we report a referenced broadband pump-compressed continuum probe half-broadband (HB) 2DES spectrometer in a partially collinear geometry. To optimize signal-to-noise ratio (SNR) we implement active noise reduction referencing, which has not previously been applied in 2DES. The method is calibrated against the well characterized 2DES response of the oxazine dye cresyl violet and demonstrated at visible wavelengths on the photochromic photoswitch 1,2-Bis(2-methyl-5-phenyl-3-thienyl) perfluorocyclopentene (DAE). The SNR is improved by a factor of ∼2 through active referencing. This is illustrated in an application to resolve a low frequency mode in the excited electronic state of DAE, yielding new data on the reaction coordinate. We show that the active noise reduction referencing, coupled with the rapid data collection, allows the extraction of weak vibronic features, most notably a low frequency mode in the excited electronic state of DAE.