Megagauss in Picoseconds

The item above describes the creation of high fields; this item describes the rapid measurement of high fields. Physicists from the Tata Institute and the Institute for Plasma Research in India have recorded in detail, for the first time, the huge magnetic spike encountered by atoms in a sample bearing the brunt of an intense laser shot.

Fields as great as 27 megagauss, roughly 50 million times the strength of Earth's magnetic field, come about very quickly in the following way: the 10¹⁶-watt/cm² pump laser beam strikes an aluminum target, the surface layer of atoms is quickly ionized, and a stream of very fast electrons is released into the body of the target, inducing the huge field.

Many high-power lasers around the world study the effects of intense light upon a solid sample. The chief achievement of the Indian researchers is to look at this process with unprecedented temporal precision, monitoring the rising magnetic field in femtosecond intervals by watching the polarization of a delayed secondary laser beam reflected from the particle plasma engulfing the sample.

Femtosecond knowledge of megagauss fields might have a bearing on designs for nuclear fusion reactions, and for studying other subjects where high magnetic fields are important—NMR, Hall effect, and perhaps even fast magnetic information storage and switching devices. (Sandhu et al., Physical Review Letters, 25 November 2002; contact G. Ravindra Kumar, Tata Institute, grk@tifr.res.in; 91-22-2152971 x 2381; www.tifr.res.in )