Stimulated raman scattering as an excitation source for time-resolved excitation-emission fluorescence spectroscopy with fiber-optical sensors

For a fiber-optical sensor system based on time-resolved excitation-emissio n (TEE) fluorescence spectroscopy, stimulated Raman scatter inp (SRS) was u sed to generate simultaneously several excitation wavelengths between 250 a nd 400 nm. For a frequency-quadrupled Nd:YAG laser and a hydrogen-methane m ixture as the Raman medium, an optimum pressure and mixing ratio was identi fied. The observed pulse energies in the micro-Joule range were sufficient for remote sensing with fiber lengths on the order of 50 m. The TEE probe i s comprised of eight independent fiber-optical sensors and was interfaced t o an intensified charge-coupled device (CCD) camera with an imaging spectro graph. The system permitted a nanosecond time resolution and parts-per-bill ion detection limits, for pyrene and fluorescein. The preliminary study of a binary mixture of benzo(a)pyrene and henzo(k)fluoranthene indicates a gai n in selectivity for TEE spectra compared to time-resolved emission spectra .