By mounting mirrors on a rotating paddle, a research team led by Mark Raizen at the University of Texas at Austin has controlled and slowed the motion of a supersonic helium beam in a manner that he likens to the way a soccer player slows and redirects a soccer ball. The long-term goal is to develop the complete atom-optics components, source, beamsplitter, and lens for an atom interferometer. But there is also interesting science related to scattering effects to be done along the way, Raizen said.
One important focus of efforts to develop atom optics for precision measurements, as well as for experiments in fundamental physics, has been on laser cooling and trapping; it is typically limited to collections of relatively few atoms that have appropriate transition energies and relatively simple energy-level structures. Much work has also been done, however, to develop atom-optics approaches to work with a wider range of atoms-particularly noble-gas atoms such as helium, which would require a nonexistent 60-nm-emitting laser for cooling and trapping. These gases offer advantages for atom optics and interferometry that include the availability of high-intensity supersonic beams and specular-reflection characteristics from single-crystal surfaces of silicon and lithium fluoride, for instance.
The Texas researchers used an atomic-beam source developed by Uzi Even at Tel Aviv University (Tel Aviv, Israel) to generate a monochromatic pulsed beam of helium and neon atoms traveling at 511 m/s. Despite the rapid motion of the atomic pulses, atoms within each 10 µm pulse (a few millimeters in length) moved only a few meters per second relative to each other, yielding an equivalent temperature of about 50 mK within each pulse. The rotating paddle, with atomically flat silicon mirrors on each end rotating in the same direction as the beam, slowed the atomic pulses by about 240 m/s by absorbing energy on impact, in the same way that a soccer player might absorb some of the energy of a passing soccer ball with his or her foot (see figure).
Slowing the beam down is the first step in building an atom interferometer, as well as in doing science based on scattering experiments, because it enables removal of inelastic scattering (which scales almost exponentially with velocity) and higher diffraction orders. Raizen’s team is developing a beamsplitter (the second step) based on single-crystal surfaces that also act as reflective diffraction gratings for atoms. The team has also fabricated a lens (the third step) with a 17 cm focal length by bending a reflective wafer into a parabolic shape.
REFERENCE
1. E. Narevicius et al., Physical Rev. Lett. 98, 103201 (March 9, 2007).