RAMAN SPECTRA IN THE ELECTRONIC EXCITED STATE: CARS OF LASING RHODAMINE

Abstract

By choosing $\omega_{2}$ (4880 {\AA}) preresonant with the $S_{1}-S_{0}$ transition of rhodamine 6G, and $\omega_{1}$ (4537 {\AA}) resonant with the $S_{2}-S_{1}$ absorption, the resonant CARS spectra for lasing rhodamine 6G in methanol, ethanol and acetonitrile have been observed in the $1500 - 1650;cm^{-1}$0 range. Strong positive bands, attributed to CARS from the $S_{1}$ state, replace the negative ground state preresonant bands as the $S_{0}$ state saturates at high laser beam power densities. A water solution behaves quite differently, possibly as a result of strong association of water with rhodamine in the excited state.