PHOTOINDUCED STRAIN AS A PROBE OF ACOUSTICAL AND ELECTRONIC-PROPERTIES OF CONDUCTING POLYMERS

We discuss applications of photogenerated strain in transient absorpti on experiments. These include measurements of sound velocity, phonon d ispersion relations, and excited electronic state energy levels. In pa rticular, we have identified a new type of spectroscopy in photoinduce d absorption that can be used to detect both allowed and forbidden ele ctronic transitions in thin semiconducting films. This technique was a pplied to a host of conducting polymers for which we detected energy l evels of various excitonic states with odd and even symmetry.