Multiplex coherent anti-Stokes Raman spectroscopy using a pulsed optical parametric oscillator: comparison of broadband and two-colour techniques

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) is a form of nonlinear-optical spectroscopy that is useful for spectroscopic sensing of high-temperature media. Earlier research1 evaluated optical parametric oscillator (OPO) devices as an alternative to dye lasers in providing tunable coherent light for this purpose. Further development of the OPO CARS theme follows demonstrations2,3 of how to control the optical bandwidth and output wavelengths of a pulsed OPO with a passive ring cavity, injection-seeded by a single-mode external-cavity diode laser (ECDL). We have succeeded in injection seeding a single pulsed OPO at two separate optical frequencies that fall within its intrinsically broad optical bandwidth, using a pair of ECDLs. This OPO-based strategy enables single-shot, two-colour multiplex CARS measurements4 that can be used for combustion diagnostics, as has previously been demonstrated with dye-laser sources.5