Coherent anti-Stokes Raman spectroscopy (CARS): Improved experimental design and observation of new higher-order processes

The development of the optical and electronic arrangement which has permitted the straightforward measurement of coherent anti-Stokes Raman spectra (CARS) and of higher-order processes not previously reported is described in this paper. The CARS spectrum of a dilute solution of diphenyloctatetraene in benzene is presented. This spectrum demonstrates the significantly greater signal-to-noise ratio possible with CARS as compared to conventional Raman techniques. Higher-order Raman spectral excitation studies (HORSES) are described which indicate the presence of a six-wave or a second-order four-wave mixing process.