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K: Kurzzeitphysik

K III: HV III

K III.1: Invited Talk

Thursday, April 5, 2001, 15:30–16:15, EB107

Ultrafast Gating of Optical Pulses — •Ulrich Teubner, Ulrich Wagner, Eckardt Förster, Thomas Feurer, Karsten Michelmann, and Roland Sauerbrey — IOQ, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07443 Jena

Gating of optical pulses has a long history and effort has been made to realise shorter and shorter switch times. With the advent of femtosecond laser pulses large progress has been made and numerous applications profit from it. An example of a widely used gate is the Kerr shutter. However, although its intrinsic response time is very short, the temporal evolution of a gate is limited by the pump pulse duration. Here we show that even faster gating can be achieved by optical field ionisation. The large electric field of an intense femtosecond laser pulse can be used to rapidly ionise a transparent solid such as glass or quartz. This leads to a reduction of the originally nearly hundred percent transmission by many orders of magnitude. This reduction occurs on a time scale which is only a small fraction of the laser pulse duration and thus can be used to realise an ultrafast switch. In contrast to earlier works where so-called "plasma shutters" were investigated [1], here the optical process of gating is directly induced by the laser field and occurs on a much shorter time scale. Due to the rapid increase of the electron density the effect relies on the strong augmentation of the absorption coefficient and to a lesser extent on the increase of the surface reflectivity. Calculations of the temporal evolution of the optical properties of the material that are changed by the laser field are confirmed by experiments. In particular, it is demonstrated that a 50 fs laser pulse could induce gating times well below 10 fs.