EXCITED TRIPLET-STATE POLARIZABILITIES IN LASER-INDUCED REFRACTIVE-INDEX TRANSIENTS

Laser-induced refractive index transients in low temperature solutions are shown to be dominated by the polarizability changes due to excitation of metastable excited electronic states of solute molecules. The time-dependence of the thermal transient is worked out for the general case (intermediate between pulsed and cw thermal sources), and the thermal transient is found to be small relative to the polrizability transient if the exited state lifetime is larger than the thermal relaxation time of the solution. Estimates of the magnitudes of these effects are given for benzene in its lowest triplet state in a rigid hydrocarbon solution. Methods are given for minimizing thermal and excited state absorption effects. Application of photoselection analysis provides a method of measuring all three diagonal elements of the change in the polarization tensor upon excitation. © 1979.