Centers of Excellence: Laser Chemistry

A radically new approach to controlling chemical reactions, based on the use of laser light, is under study at the Center of Excellence headed by Weizmann Institute Prof. Moshe Shapiro.

Known as coherent control, the approach was pioneered by Weizmann Institute Prof. Shapiro and University of Toronto Prof. Paul Brumer over a decade ago. These days, this laser method is arousing great interest -- in large part because of its potential applications for industrial chemistry, paving the way for the more efficient manufacture of a variety of products, from pharmaceutical drugs to superfast optical switches.

The desire to use laser beams to break chemical bonds between molecules is not new. But previous attempts largely failed to meet the challenge of breaking a single bond without affecting others.

Coherent control, the Shapiro-Brumer approach, has addressed the problem by using a laser beam to excite the wavelike aspects of molecules. Inside the molecules, as in a stormy sea, two waves that meet crest to crest will produce an even bigger, deeper wave. Conversely, when the waves meet crest to trough, they extinguish each other. Shapiro and Brumer exploited these effects in order to direct chemical reactions so as to break specific molecular bonds, thereby producing the desired reaction products.

In an experiment reported earlier this year in the scientific literature, Shapiro, Brumer and their colleagues at the Weizmann Institute and University of Toronto demonstrated for the first time that it is also possible to use laser light to control the quantity of materials produced in a chemical reaction. By varying the wavelengths of the laser beams, they were able to increase the yield of one product produced in the reaction, while decreasing that of another.

Shapiro cautions, however, that there are numerous obstacles to overcome before coherent control can be used for large-scale industrial technology. But if these limitations are overcome the technique could, for instance, revolutionize the pharmaceutical industry by providing a fast and efficient method for producing righthanded or lefthanded forms of compound. Like our hands, molecules often exist in two mirror forms, or enantiomers, one of which is biologically active and the other either inactive or harmful. Today pharmaceutical companies expend considerable time and money to produce the correct form of these molecules for drugs.

Coherent control may also lead to novel technologies, such as improved optical switches for semiconductor devices that are many times faster than existing ones, as well as lasers that emit supershort bursts of light that are a tenth the length of ones now in use.

This new Center of Excellence includes four research groups, two of them at the Weizmann Institute -- one headed by Shapiro and the other by Prof. David Tannor, another pioneer of coherent control who recently joined the Institute from the University of Notre Dame. The other two teams are led by scientists from the Hebrew University of Jerusalem. Shapiro and Tannor are members of the Chemical Physics Department .