Abstract

Multiple femtosecond excitation pulses have been used recently for increased control over molecular motion. Several developments in this direction will be discussed. For excitation pulse sequences with many (i.e., more than two or three) pulses, computer control over the generation of the pulse sequence is essential. It is important to be able to analyze the molecular of material response to a given pulse sequence and generate a new, optimized pulse sequence on the spot. Multi-element liquid crystalline masks can be used to do this. The analysis of material responses and design of new masks could be done by the human experimenter or, ideally, by computer. Real-time, single-shot femtosecond data acquisition is also essential for condensed materials in which the goal of multiple-pulse excitation is controlled chemical or structural change. Much current effort is directed toward gas-phase samples in which a buildup of reaction product can be avoided by continuously flowing new material into the irradiated region. Most applications will involve crystals, polymers, and other nonflowable media. Multiple femtosecond probe pulses can be used to collect all the necessary temporal information after just one excitation event. In this manner fundamental and applied experiments can be conducted on condensed-phase materials.

© 1992 Optical Society of America