IN A GRAVITO-OPTICAL SURFACE TRAP (GOST), cesium atoms, cooled first in a magneto-optical trap (MOT, which employs magnetic fields and laser beams to confine and cool atoms), are allowed to fall downwards onto a prism. When the atoms strike the prism, they are reflected upwards by the electromagnetic fields associated with "evanescent waves" which arise from a beam of laser light grazing the prism from beneath. The atoms are not only reflected, but lose some of their energy to the waves. After several bounces, the atoms collect in a chilled, essentially two-dimensional, cloud. In this way physicists at the Max-Planck Institute in Heidelberg (Rudolf Grimm, rudolf.grimm@mpi-hd.mpg.de) cooled Cs atoms from a temperature of 10-15 micro-K (in a MOT) down to 3 micro-K.The GOST approach might be helpful in producing Bose- Einstein condensates because (1) it is able to trap a much higher density of atoms than is possible with MOT's, thus creating a better starting point for the next stage in the Bose- Einstein process, evaporative cooling (see Update 305); (2) it is effective in trapping the atoms in all their magnetic varieties (some atoms, whose magnetic orientation is altered during collisions, would otherwise be lost from the trap); and (3) it might offer the chance to study 2-dimensional condensates since the atoms start out in a planar configuration. (Ovchinnikov et al., Physical Review Letters, 22 Sept.; see figure at Physics News Graphics.) By the way, the first report of a Bose-Einstein Condensate in a European lab comes from last week's European Research Conference on Quantum Optics at Castelvecchio Pascoli in Italy. Gerhard Rempe of the University of Konstanz (gerhard.rempe@uni-konstanz.de) gave preliminary evidence for a rubidium-87 condensate in a "Ioffe-Pritchard" trap.

A LIQUID MAGNETIC FROTH, created and studied by University of Paris researchers (Cyrille Flament, flament@aomc.jussieu.fr), can display reversible, magnetically controlled patterns on its surface. Perhaps the most common example of a froth is a soap-and-water mixture. In general, a froth is any solid or liquid containing uniformly dispersed solid particles as well as homogeneously distributed gas molecules. Combining oil with a magnetic fluid (cobalt ferrite particles suspended in a water-based solution), and placing the resulting froth between two glass plates, the researchers applied magnetic fields to create 2-D patterns consisting in some cases of 4-to 7-sided "cells" of oil separated by magnetic fluid. Decreasing the intensity of the magnetic field could change, for instance, the number of 5-sided cells. Unlike other froths, such as a soap-and-water mixture, the topological features of the pattern could return by increasing the field again. One could conceivably use these films to test ideas about the surfaces of other physical systems, such as the space-time fabric of the early universe. For example, placing a bar magnet on top of the froth could introduce an instability; once the magnet is removed, the evolution of the system could then be studied. (Florence Elias et al., Physical Review E, Sept. 1997; figures at Physics News Graphics.)

MARS HAS A MAGNETIC FIELD. The field, measured by the Global Surveyor spacecraft newly arrived at Mars, is much weaker than Earth's, but might (at an earlier epoch) have afforded hypothetical life forms on Mars a small buffer against lethal incoming solar wind particles. The Global Surveyor will now put itself into a circular orbit by using Mars' tenuous atmosphere as a brake during successive passes. (Science News, 20 Sept. 1997.)