Coherent Raman Scattering in Thin Film Waveguides

The field localization associated with planar integrated optics makes a thin film an ideal medium for performing nonlinear optics phenomena with moderate total powers. To date, primarily second order processes1–3 have been demonstrated. Coherent Anti-Stokes Raman Scattering, i.e. CARS (CSRS) is a third order process in which two photons at ω1 combine with one photon at ω2 (or vice-versa) to produce a photon at the frequency ω3=2ω1−ω2 (or ω3=2ω2−ω1). The resulting signal is enhanced when ω1−ω2 coincides with a vibrational Raman transition in the molecules which make up the medium and hence sweeping the difference frequency yields the Raman spectrum of the medium. This process promises sensitivities orders of magnitude larger than for spontaneous Raman scattering which has already been observed in thin film waveguides4.