EXCITED-STATE SPECTROSCOPY OF ORGANIC-DYES BY USE OF POPULATION GRATINGS

Excited-state spectroscopy of organic dyes is demonstrated with a lase r-induced grating technique. The basis of this method is the creation of a population grating in the material that is being investigated and the use of a probe detuned from the pump,; permitting a great increas e in effective contrast. The absorption-emission spectrum of transitio ns from S-1, the first singlet state, were determined from the diffrac ted signal of the tunable probe laser. The resulting theory of the gra ting function and the results of experiments on Nile Blue and Rhodamin e 640 are presented. In conjunction with other techniques such as flas h photolysis, population gratings may provide useful information on ex cited-state structures of dye molecules.