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Lasers

Lasers

Making light of a difficult phase

01 Apr 2003

Physicists are always striving to gain control over matter at the quantum level, and ultrafast lasers are just about the best way of achieving this. By precisely controlling the intensity, wavelength and duration of extremely short pulses of light, we can manipulate electronic processes at the atomic level.

If these pulses can be shortened to the scale of attoseconds, then the electromagnetic fields within them will be changing on the same timescale as the motion of the electron. This means that physicists can use the pulses to steer electrons with astonishing precision, and control processes such as the emission of light and chemical reactions.

Until now, however, there has been a fundamental obstacle to the production of such short pulses. At the sub-femtosecond level, a laser pulse contains only a few cycles of the carrier electromagnetic wave. As the pulse evolves the carrier wave can therefore become out of phase with the amplitude envelope, which can lead to a variety of different electric-field waveforms. This makes it difficult to put the pulse to any constructive use. The difference in phase between the carrier and envelope waves is called the carrier-envelope phase (CEP), and controlling it precisely is essential for a new generation of experiments that will probe and manipulate processes that occur on a sub-femtosecond timescale.

Now physicists in Vienna and Germany have managed to do just that, allowing the carrier-envelope phase of a high-power ultrashort pulsed laser to be altered at will. With this set-up they were able to control electrons at the scale of 250 as (250 x 1018s), and they claim that their technique is limited only by the most fundamental barrier we know – quantum-mechanical uncertainty (A Baltuska et al. 2003 Nature 421 611).

This article by John Tisch and Jon Marangos from the Department of Physics at Imperial College, London can be read in full in the April issue of Physics World.

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