Efficient Rejection of Fluorescence from Raman Spectra Using Picosecond Kerr Gating

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Abstract
An efficient method for the rejection of fluorescence from picosecond time-resolved resonance Raman (ps-TR3) spectra, applicable also to ground-state Raman spectroscopy, has been demonstrated. The technique removes fluorescence from Raman light in the time domain using a Kerr gate driven by 110 μJ, 1 ps pulses at 800 nm and a repetition rate of 0.65 kHz, giving a response time of ∼ 3 ps, representing the highest time resolution achieved experimentally for rejecting fluorescence from Raman spectra. The effectiveness of the method is proven by measuring Raman solvent bands and ps-TR3 spectra of S1 p-quaterphenyl from solutions contaminated with the laser dye DCM using laser wavelengths which excite the dye and so produce intense fluorescence emission. The optical transmittances accounting for losses in the optical elements and losses due to incomplete polarization rotation in the Kerr medium in the open and closed states were 15% and 0.005%, respectively. The use of the gate in a time-resolved fluorescence measurement of DMABN is also demonstrated.