In the early 90s, ultrashort laser pulses provided scientists with new possibilities for very fast processes. Previously unthinkable applications in measuring technology, medicine and material processing became conceivable. The saturable absorber mirror by Prof. Dr. Ursula Keller has now laid the groundwork for the use of ultrafast pulse lasers in industrial applications. For this development she gets the first prize of the Berthold Leibinger Innovationspreis 2004.

Laser physicists refer to pulses as ultrashort only when light pulses last less than a millionth of one hundredth of a second. They are faster than the typical duration of the interaction between particles: while the material exposed to an ultrashort laser pulse evaporates, the edge remains cold.

Ultrashort pulses are generated with an optical effect called "mode coupling". The light is not switched on and off, but rather fast pulses occur automatically as a result of a special superimposition of laser light waves: the modes. So far many optical elements are required to realize mode coupling. Ultrashort lasers were therefore usually sensitive and could only be used in laboratory conditions.

The SESAM – SEmiconductor Saturable Absorber Mirror – by Prof. Dr. Ursula Keller is a simple optical element used to activate mode coupling. This saturable absorber mirror is made of overlaid semiconductor layers. It has the special property of generating ultrashort pulses simply and reliably. All that is required to install it as an mirror in appropriate lasers.

With the invention of the SESAMs she has made it possible to bring the ultrafast laser out of the laboratory. In 1992 the full professor of experimental physics and the head of the Ultrafast Laser Physics Laboratory invented this saturable absorber mirror at Bell Labs in the U.S.A and then she further developed them experimentally and theoretically at ETH in Zurich. In the meantime, SESAMs are being used in commercial beam sources around the world. In 1994, Prof. Keller and Dr. Kurt Weingarten founded the company Time-Bandwidth Products AG to market SESAM, which she patented and trademarked.

Digital pictures of the prize winners and the awarded work and translations of this press-release in more languages are available at www.leibinger-stiftung.de.