Imaging an atomic beam in two dimensions

B. Sheehy, S-Q. Shang, Richard N. Watts +2 more

We report the use of frequency-chirped diode lasers to decelerate a thermal atomic beam of Rb and, in a separate experiment, the use of frequency-stabilized diode lasers to collimate the beam with optical molasses. For this we used a 100-mW cw laser-diode array injection locked to light from a low-power, frequency-narrowed, single-stripe diode laser. Also, a novel scheme for imaging the neutral-atom beam profile has been developed for monitoring the collimation experiments in two dimensions. We have increased both beam brightness and intensity by a factor of more than 20.

Wilhelm G. Kaenders, Frank Lison, A. Richter +2 more

B. Sheehy, S-Q. Shang, Harold J. Metcalf +1 more

We have developed a method to image a beam of neutral atoms (chiefly usable for alkalis) that is essentially an extension to two dimensions of the usual hot wire method of detection. The beam of neutral atoms first passes through a a highly transparent, positively charged grid and then impinges on a heated grid of electroformed nickel with lower transparency and at ground potential. Atoms with ionization potential less than the work function of Ni that strike the heated grid are ionized at its surface and are then pushed through it by the 250-V/cm field produced by the voltage on the first grid. The ions are then accelerated through ~700 V to a pair of multichannel plates (MCPs) ~3 mm away where the single charged ion signal is amplified. The output electrons from the MCPs are accelerated by 1.7 kV to a phosphor screen ~3 mm away that glows when the electrons strike it. The phosphor screen is viewed by a TV camera whose output goes to a frame processor in a PC. The system has been used for studying transverse laser cooling (optical collimation) of a Rb beam done with diode lasers.

David S. Weiss

O. Carnal, M. Sigel, Tycho Sleator +2 more

Focusing of and imaging with atoms by means of a spherical Fresnel zone plate has been observed for the first time. An intense beam of metastable helium atoms with atomic de Broglie wavelength ${\ensuremath{\lambda}}_{\mathrm{dB}}$=0.5--2.5 \AA{} is passed through either a single or a double slip with dimensions in the 10-\ensuremath{\mu}m range. This transverse intensity distribution is imaged by a Fresnel zone plate, 210 \ensuremath{\mu}m in diameter and with an innermost zone diameter of 18.76 \ensuremath{\mu}m. For ${\ensuremath{\lambda}}_{\mathrm{dB}}$=1.96 \AA{} the focal length is 0.45 m. The imaging properties of the zone plate are presented and compared with numerical calculations.

Karl D. Nelson, Xiao Li, David S. Weiss