2-PHOTON WAVE-PACKET INTERFEROMETRY

The excitation of a molecule by a short pulse creates a wave packet whose motion depends on the nuclear forces of the excited electronic state. The properties of such a packet can be studied interferometrically. This is done by exposing the molecule to two identical pulses delayed from each other. Two packets are thus created and the excited state population has a term which depends on the interference between them. This interference population is a quantum effect and its dependence on the delay time reflects the coherence properties of the packet and is very sensitive to the potential energy surface. In this paper, we examine the use of wave-packet interferometry to study the dynamic properties of packets created by two-photon absorption. We find several interference populations since the packets created by two-photon absorption interfere with each other and with packets created by absorption of one photon from each pulse. The single interference terms contain different physical information and we discuss how each can be measured separately. This method provides a sensitive way for studying the dynamic properties of high energy electronic states that can be reached by two-photon absorption.