Berlin 2001 – wissenschaftliches Programm

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PV: Plenarvorträge

PV II

PV II: Plenarvortrag

Dienstag, 3. April 2001, 09:00–09:45, H105

Quantum control of reaction dynamics by adaptive femtosecond pulse shaping — •Gustav Gerber — Physikalisches Institut, Universität Würzburg, Germany

For more than 30 years now, starting with the invention of the laser, many scientists worldwide have tried to develop methods which use laser radiation as a means to control the outcome of chemical reactions. The major goal of these efforts is to be able to break or make chemical bonds selectively on a microscopic level. A suitable realization of this scheme could imply a revolution of synthetic chemistry. Desired products could be generated with higher efficiencies whereas unwanted or even harmful byproducts could be suppressed. It would also be possible to produce novel substances. The method uses optimally shaped femtosecond laser pulses which are prepared by a computer-controlled laser pulse shaper in connection with an evolutionary learning algorithm. Starting with some arbitrary pulse shape, the product yields of the chemical reaction are measured instantaneously and processed by the computer algorithm in order to improve the applied laser pulses. According to the principle of "the survival of the fittest", optimum pulse shapes are found after sufficiently many cycles of the evolutionary process. The desired reaction products are then finally produced with maximum efficiency. Surprisingly, it is not necessary to provide any knowledge about the reaction mechanism or about the molecules involved. The optimization is controlled solely by the learning computer algorithm, which uses concepts taken from the biological evolution. The experimental method of selective control of molecular dynamics by feedback–optimized femtosecond laser pulses constitutes a breakthrough in the area of control of chemical reactions. Due to the universality of computer–controlled learning optimization of ultrashort laser pulses, a broad field of applications opens up in all areas which use femtosecond laser technology, such as in physics, chemistry, biology, or material sciences.

[1] Femtosecond Pulse Shaping by an Evolutionary Algorithm with Feedback, T. Baumert, T. Brixner, V. Seyfried, M. Strehle, G. Gerber, Appl. Phys. B 65, 779-782 (1997).

[2] Teaching lasers to control molecules, R. S. Judson, H. Rabitz, Phys. Rev. Lett. 68, p. 1500 (1992).

[3] Control of Chemical Reactions by Feedback-Optimized Phase-Shaped Femtosecond Laser Pulses, A. Assion, T. Baumert, M. Bergt, T. Brixner, B. Kiefer, V. Seyfried, M. Strehle, G. Gerber, Science 282, 919-922 (1998).