Double Resonance Excitation of Fluorescence in the Condensed Phase—An Alternative to Infrared, Raman, and Fluorescence Spectroscopy

The feasibility of performing a double resonance excitation of fluorescence from molecules in a condensed phase is discussed. A vibrational excitation can be created by either stimulated Raman scattering or infrared absorption while a second excitation can excite the molecule to an excited electronic state from which fluorescence can occur. By providing high rates of excitation, one can overcome the rapid vibrational relaxation rates to produce fluorescence. By scanning the second excitation frequency in synchronization with either the infrared frequency or the difference frequency producing the stimulated Raman scattering, one can obtain spectra that are analogous to Raman or infrared spectra. This approach would have the sharp lines characteristic of Raman or infrared spectroscopy but would have an increased sensitivity characteristic of fluorescence spectroscopy.