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Number 407, December 21, 1998 by Phillip F. Schewe and Ben Stein
RELATIVISTIC NONLINEAR OPTICS. Laser light is a convenient way of transporting both electric and magnetic fields. When an electron encounters light, however, it is usually the electric field that does the talking; the magnetic part of light is less influential since its effect on the electron is proportional to the electron's speed as a fraction of the speed of light (c). In new experiments at the University of Michigan this is all changed since the intensity of the laser light used is so great (a terawatt of power, compared to a milliwatt for a laser in a CD player) that the electrons in an oncoming supersonic beam of helium atoms are stripped from their parent atoms and accelerated to relativistic speed (a fair fraction of c). With the magnetic component now exerting a tangible force, the electrons' motions become loopy---that is, the electrons do not scatter in straight lines from the laser electric field but instead acquire a figure-eight motion. This "nonlinear Thomson scattering" causes the electrons to emit higher-frequency versions (harmonics) of the original laser light in a characteristic pattern. It was precisely the emission of harmonic light by intense light striking slow electrons bound to atoms (also at the University of Michigan) that helped to establish nonlinear optics in the early 1960's. Now the scattering of intense light from fast free electrons helps to establish an era of relativistic nonlinear optics, one goal being the generation of coherent x rays. (Chen et al., Nature, 17 Dec.; contact Donald Umstadter, dpu@eecs.umich.edu,734-763-2284.)
GLUON FUSION might be the shortcut to finding Higgs bosons. As the hypothetical particle which supposedly endows other particles with mass, the Higgs is an important ingredient in the standard model of particle interactions and one of the chief quarries at present and future accelerators. In fact, a new calculation shows that the Higgs might even be found at the rejuvenated Tevatron at Fermilab if the Higgs mass (still unknown) is less than 180 GeV. This prognosis counts on the ability of colliding protons and antiprotons to send forth gluons which then fuse to form a Higgs, which would thereafter decay into a pair of W bosons (carriers of the weak force). Previous studies pondering the likelihood for Higgs production were based chiefly on the notion that the proton-antiproton collisions would make a Higgs via quark- antiquark fusion in the company of a W, and had estimated that the Tevatron would be capable of spotting Higgs particles with masses no larger than about 130 GeV. At a recent meeting at Fermilab on Higgs prospects in the next round of work at the Tevatron, experimentalists were heartened by the new estimates since naturally they would like to explore as large a Higgs window as possible. (Tao Han and Ren-Jie Zhang, Physical Review Letters, 4 Jan 1999; than@pheno.physics.wisc.edu or 608-262-2865; Tao Han, Andre Turcot and Ren-Jie Zhang, http://xxx.lanl.gov/hep-th/9812275.)
A MULTI-WAVELENGTH SEMICONDUCTOR LASER, one which emits light at three separate colors using only a single material, has been achieved at Lucent Technologies. This result is an extension of Federico Capasso's work with cascade lasers (see Updates 322, 359), in which the laser wavelength is determined not by semiconductor chemistry but by the thickness and spacing of a series of tiny semiconductor layers. The present device can emit three different mid-infrared wavelengths simultaneously, making it useful as the basis for a detector of trace gases (e.g., in monitoring pollutants). (Tredicucci et al., Nature, 26 Nov. 1998.)
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