A common problem encountered in Raman spectroscopy is the presence of fluorescence swamping the weaker Raman signal. The Kerr gated Raman collection system removes fluorescence background enabling measurements of even strongly fluorescing samples. Fluorescence is rejected in the time domain with the Kerr gate acting as an optical shutter with ca 4 ps time resolution. The gate throughput in the open state is as high as 40 % with an extinction ratio in the closed state of ca 10-5. Currently the Kerr gate can be operated in the range 300-700 nm.
Schematic of the Kerr-gated Raman setup (P Matousek, M Towrie, A Stanley, AW Parker, Applied Spectroscopy 53, 1485-1489, 1999) and Raman spectrum of unleaded petrol with and without the Kerr-gate, λex = 400 nm (1 ps, 4 mJ, 1 kHz), 400 s acquisition (P Matousek, M Towrie, C Ma, WM Kwok, D Phillips, WT Toner, AW Parker, J Raman Spectrosc. 32(12), 983-988, 2001. DOI: 10.1002/jrs.784).