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Journal of Applied Physics

Optical collimation and compression of a thermal atomic beam

Chun-Cheng Tsao, Youjun Wang, J. Weiner, Vanderlei Salvador Bagnato

Published Jul 1, 1996• 21 citations
Publisher

Abstract

We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group.

DOI
10.1063/1.362774

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We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group.
We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about $2\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}∕\mathrm{s}$ at a total cooling laser power of 55mW55\phantom{\rule{0.3em}{0ex}}\mathrm{mW}55mW. It has a narrow longitudinal velocity distribution with mean velocity 15m∕s15\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}15m∕s with full width at half maximum 3.5m∕s3.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}3.5m∕s and has a low divergence of 26mrad26\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}26mrad. The high flux enables ultrafast loading of about 1010{10}^{10}1010 atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.
An atomic beam has been collimated, compressed, and deflected simultaneously by an atomic beam guide based on an tilted one-dimensional magneto-optical trap. Isotope-selected rubidium atoms were extracted from the naturally-mixed thermal atomic beam. We could extract more than 50% of the incident atoms as a deflection beam when we combined this deflection technique with the atomic deceleration using a broadband spectral light. We could manipulate the transverse displacement of the deflected beam precisely by modifying the quadrupole magnetic field. We also observed the well-collimated atomic beam to be channeled into the dipole force potential valleys formed by the standing wave light field.
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We report on the transverse laser cooling of a magnetically guided beam of ultracold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section, heat is extracted from the atom beam by a two-dimensional (2D) optical molasses perpendicular to it, resulting in a significant increase in atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that, by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses and longitudinal heating can be avoided. Final temperatures below 65 μK have been achieved, corresponding to an increase in phase space density in the guided beam by more than a factor of 30.
We have developed a rubidium atomic funnel for use as a matter-wave source in experiments in atom interferometry and atom optics. The funnel utilizes the techniques of laser cooling and trapping to produce a low-velocity beam of cold rubidium atoms. Atoms from a thermal beam are first slowed in a tapered magnetic field using 1D Zeeman slowing. The atoms are then loaded into a 2D magneto-optic trap or atomic funnel. The trap cools and compresses the atoms, which are then ejected from the trap by moving molasses formed with frequency-shifted laser beams. These slow atoms will be diffracted by microfabricated transmission gratings as part of a three-grating atom interferometer.
It is helpful to make full use of the laboratory space by simplifying the cold atom experimental system, especially in the area of aerospace and precision measurement. We present a two-dimensional magneto-optical trap (2DMOT) for sodium atoms, whose magnetic field is produced by four sets of permanent magnets, and the residual field in the vertical direction is used for a Zeeman slower. The atoms are cooled and trapped in a 2DMOT which provides a highly efficient atomic flux for three-dimensional magneto-optical trap (3DMOT) in a high-vacuum chamber. The maximum 3DMOT loading rate is measured to be 2.3 × 109/s by optimizing the parameters of the Zeeman slower and the 2DMOT. The atom number trapped in 3DMOT is 6.2 × 109. The 2DMOT designed by using permanent magnets has the property of compact structure and simple size, which can be used to cool and trap other neutral atoms.