Fluorescence suppression in resonance Raman spectroscopy using a high-performance picosecond Kerr gate

A high-performance Kerr gate designed for the suppression of fluorescence in both time-resolved and steady-state resonance Raman spectroscopy is described and its performance illustrated. This is an improved version of a system described recently, with superior extinction ratio, higher throughput and wider usable spectral range. Specially designed polarizers are an essential feature of the system. The gate opens for ∼4 ps at 1 kHz repetition rate, throughput in the open state is up to ∼40% (excluding Fresnel losses on optical elements), the extinction ratio in the closed state is 10-5 and the usable spectral range is 300-700 nm with a single set of polarizers. The Kerr gate is driven by ∼500 μJ, 1 kHz, 1 ps laser pulses at 800 nm and we believe that it is currently the most powerful device in operation for the temporal rejection of fluorescence from Raman spectra. It increases the general applicability of Raman spectroscopy as illustrated by picosecond time-resolved resonance Raman spectra of the intramolecular charge transfer state of 4-dimethylaminobenzonitrile and by the ground-state Raman spectrum of unleaded petrol at 400 nm probe wavelength.