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AIP conference proceedings

Transverse magneto-optical compression of a frequency-chirping slowed cesium atomic beam

P. Pillet, Jia Yu, J. Djemaa, P. Nosbaum

Published Jan 1, 1993• 2 citations
Publisher

Abstract

We have transversally compressed a monokinetic cesium atomic beam in a 2D magneto‐optical trap (MOT), also called a funnel, on the F=4→F’=5 transition of the cesium D2 line. The longitudinal cooling is obtained by frequency‐chirping. Preliminary results show a final diameter of about 50–100 μm with a density of a few 108 atoms/cm3 for slowed atoms. The density is enhanced by a preliminary orientation of the atoms inside the trap.

DOI
10.1063/1.45082

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Transverse magneto-optical compression of a frequency-chirping, slowed cesium atomic beam

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We have transversally compressed a monokinetic cesium atomic beam in a 2D MOT1,2 on the F=4→F′=5 transition of the cesium IX, line. The longitudinal cooling was obtained by frequency-chirped diode lasers.3 Preliminary results have been obtained showing a final diameter of about 50pm and a density of 108at./cm3. We have studied the specificities of a multi-V system as the transition F=4→F′=5 in the cesium atom. Originally proposed for a three-level V-type atomic system4, the process can be easily generalized to F→F+1 (F>=1) transitions. In this case, the atom is assumed to be polarized into the Zeeman sub-level Mf=-F with respect to the local magnetic field inside of the trap. For a non-polarized statistic mixture, two effects modify the compression process. The first one is due to the large variation in the Clebsch-Gordan coefficients.3 The second one comes from the difference between the Larmor frequencies associated to the lower and the upper levels. The both effects lead to a mF-dependent restoring force. Efficient compression can be obtained by preparing the atomic population in the “good” Zeeman sub-levels, |MF|=F. Two methods have been explored in our experiments to polarize the atomic beam. The first one used an additional blue-detuned laser beam to increase the atomic population in the |MF|=f Zeeman sub-levels by optical pumping. In the second one, the σ-polarized cooling laser beam orientated the atomic population in the axial direction during the slowing process. This orientation was adiabatically transformed into transversal ones by entering in the trap. Further experiments are in progress.

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Study of a bright, slow, and cold cesium source for a continuous beam frequency standard

P. Berthoud, E. Fretel, P. Thomann

To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45/spl deg/ laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2/spl times/10/sup 8/ at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 /spl mu/K, additional transverse cooling even reduces the transverse temperature in one dimension below 30 /spl mu/K. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7/spl times/10/sup -14//spl tau//sup -1/2/. Other applications of continuous beams of cold atoms are suggested.

Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Jan 22, 2003•2 citations
We have transversally compressed a monokinetic cesium atomic beam in a 2D magneto‐optical trap (MOT), also called a funnel, on the F=4→F’=5 transition of the cesium D2 line. The longitudinal cooling is obtained by frequency‐chirping. Preliminary results show a final diameter of about 50–100 μm with a density of a few 108 atoms/cm3 for slowed atoms. The density is enhanced by a preliminary orientation of the atoms inside the trap.
We have transversally compressed a monokinetic cesium atomic beam in a 2D MOT1,2 on the F=4→F′=5 transition of the cesium IX, line. The longitudinal cooling was obtained by frequency-chirped diode lasers.3 Preliminary results have been obtained showing a final diameter of about 50pm and a density of 108at./cm3. We have studied the specificities of a multi-V system as the transition F=4→F′=5 in the cesium atom. Originally proposed for a three-level V-type atomic system4, the process can be easily generalized to F→F+1 (F>=1) transitions. In this case, the atom is assumed to be polarized into the Zeeman sub-level Mf=-F with respect to the local magnetic field inside of the trap. For a non-polarized statistic mixture, two effects modify the compression process. The first one is due to the large variation in the Clebsch-Gordan coefficients.3 The second one comes from the difference between the Larmor frequencies associated to the lower and the upper levels. The both effects lead to a mF-dependent restoring force. Efficient compression can be obtained by preparing the atomic population in the “good” Zeeman sub-levels, |MF|=F. Two methods have been explored in our experiments to polarize the atomic beam. The first one used an additional blue-detuned laser beam to increase the atomic population in the |MF|=f Zeeman sub-levels by optical pumping. In the second one, the σ-polarized cooling laser beam orientated the atomic population in the axial direction during the slowing process. This orientation was adiabatically transformed into transversal ones by entering in the trap. Further experiments are in progress.
A beam source is proposed for the production of an intense cold cesium atomic beam that can be used in cesium beam atomic clocks. The source is based on a two-dimensional magneto-optical trap (2D-MOT), but introduces hollow cooling and pushing lights in the axial direction to create a 2D+-MOT, which separates the cooling and pushing functions while the low-power pushing light pushes atoms out to form a cold atomic beam. This cold cesium atomic beam source reduces the light shift due to leakage light and retains longitudinal cooling to increase the flux of the cold atomic beam compared with that of the conventional 2D+-MOT scheme. The specifics of the design are investigated, the atomic velocity and beam flux are calculated, and the results are experimentally verified. The results demonstrate that when the power of the pushing light is 180 µW and when its frequency resonates with the 4 → 5′ transition of the Cs D2 line, the most probable longitudinal velocity of the outgoing cold atomic beam, the width of velocity distribution, and the atomic beam flux are 19.38 m/s, 8.1 m/s, and 1.7 × 1010 atoms/s, respectively.
We describe the design and performance of a slow atom source based on a 2D magneto-optical trap (MOT) that uses an innovative simple optical configuration. Metal-coated retro-reflecting prisms replace mirrors and quarter-wave plates so the optical power of the cooling laser beam is recycled. This source has been characterised for three different configurations: with and without transverse magnetic field gradient, and with a pusher beam to obtain a 2D+-MOT. The longitudinal velocity is of the order of 25 m·s−1, with a transverse velocity spread ≤1 m·s−1, while the typical atomic flux density obtained is up to 1.3×1014 at ·s−1·m−2 for a cesium vapour pressure of ~4×10−8 mbar in the source. We use this slow atom beam, instead of cesium vapour, to load a 3D moving optical molasses that feeds a continuous cold atom fountain. We obtain a gain of a factor ~20 in the atomic flux launched by the fountain.
Simulation of two-dimensional (2D) transverse laser cooling of Cs atomic beam from pyramidal magneto-optical trap atom funnel (PMOTAF) conceived for atom lithography is presented. The results show that both the minimum full width at half maximum (FWHM) and the maximum peak value of the spatial profile of the atomic beam occur at the frequency detuning of optical molasses equals to -0.5 Г. Moreover, for each frequency detuning, an increase in the intensity of the optical molasses leads to smaller FWHM and higher peak value. The not negligible role of gravity on the atomic beam of sub-thermal longitudinal velocity along the horizontal direction is that every atomic trajectory possesses a parabolic motion either before or after laser cooling which leads to a noticeable displacement of the peak value at the observation plane with respect to the starting point.
We present a 2D magneto-optical trap (MOT) that uses an innovative simple optical configuration. Instead of mirrors and quarter-wave plates we use metal-coated retro-reflecting prisms so as to recycle the optical power of the cooling laser beam. We have characterised this source for three different configurations: with and without transverse magnetic field gradient, as well as with a pusher beam to produce a 2D+-MOT. The longitudinal velocity is about 25 m·s-1, with a transverse velocity spread ≤ 1 m·s-1, while the typical atomic flux density can be as much as 1.3×1014 at·s-1·m-2 for a cesium vapour pressure of ~4×10-8 mbar in the source. We use this low velocity atomic beam, instead of thermal vapour, to load a 3D moving optical molasses that launches a continuous cold cesium fountain. We achieve a gain of a factor ~ 20 in the fountain's atomic flux.
To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45/spl deg/ laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2/spl times/10/sup 8/ at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 /spl mu/K, additional transverse cooling even reduces the transverse temperature in one dimension below 30 /spl mu/K. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7/spl times/10/sup -14//spl tau//sup -1/2/. Other applications of continuous beams of cold atoms are suggested.