2-PHOTON WAVE-PACKET INTERFEROMETRY

The excitation of a molecule by a short pulse creates a wave packet wh ose motion depends on the nuclear forces of the excited electronic sta te. The properties of such a packet can be studied interferometrically . This is done by exposing the molecule to two identical pulses delaye d 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 exa mine the use of wave-packet interferometry to study the dynamic proper ties of packets created by two-photon absorption. We find several inte rference populations since the packets created by two-photon absorptio n interfere with each other and with packets created by absorption of one photon from each pulse. The single interference terms contain diff erent physical information and we discuss how each can be measured sep arately. This method provides a sensitive way for studying the dynamic properties of high energy electronic states that can be reached by tw o-photon absorption.