Pulse-sequenced coherent anti-Stokes Raman scattering spectroscopy: a method for suppression of the nonresonant background

A new technique for suppressing the nonresonant contribution to the coherent anti-Stokes Raman scattering (CARS) signal is presented. This involves two-laser three-beam CARS generation using picosecond pulses in which one of the pump beams is delayed with respect to the two others. A reduction of 2 orders of magnitude is obtained for the 656-cm−1 vibrational line of CS2 in a 10% mixture of CS2 in toluene. This reduction is limited by the ratio of the energy in our pulse laser to that in its trailing background, which is about 100:1. Use of alternative laser systems would reduce the background by about 1012:1.