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An optically guided atomic fountain

Hilary Jane Davies

Published Jan 1, 1999• 0 citations
OpenAlex

Abstract

This thesis describes the development of a laser-cooling experiment aimed at efficient transfer of cold atoms over a short distance, for loading into a conservative atom trap. We detail the construction of a 3D magneto-optical trap (MOT) and perform characterisation measurements to optimise the number and temperature of the cold atoms. The atoms are launched vertically in a fountain from the MOT using a 'moving molasses' technique and a red-detuned far-off-resonant laser beam is used to guide them into an UHV chamber. Loading into the guiding beam is optimised with respect to the beam and MOT parameters. We demonstrate a maximum loading of 20% and guiding over a distance of more than 10 cm without loss of atoms. The atoms are delivered to the UHV chamber in a cloud with a transverse dimension of order 200 #mu#m. We discuss the extension to continuous operation of the guided atomic fountain. The 3D MOT is replaced by a funnel with 2D trapping and 3D cooling which continuously extracts the cold atoms using moving molasses. A comparison between the flux of guided atoms obtained in a pulsed fashion from the 3D MOT and continuously from the funnel indicate that the pulsed case is a factor of ten more efficient. The difference is due to inferior loading from the funnel. The optically guided fountain is used to load an optical dipole trap in the UHV chamber, using an 'optical trap door'. No additional cooling is required. The dynamics of the atoms in the optical dipole trap are studied. We discuss multiple loading of a conservative trap with the view of accumulating more atoms than can be obtained in a MOT. (author)

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European Frequency and Time Forum•Mar 27, 2006•1 citation
This thesis describes the development of a laser-cooling experiment aimed at efficient transfer of cold atoms over a short distance, for loading into a conservative atom trap. We detail the construction of a 3D magneto-optical trap (MOT) and perform characterisation measurements to optimise the number and temperature of the cold atoms. The atoms are launched vertically in a fountain from the MOT using a 'moving molasses' technique and a red-detuned far-off-resonant laser beam is used to guide them into an UHV chamber. Loading into the guiding beam is optimised with respect to the beam and MOT parameters. We demonstrate a maximum loading of 20% and guiding over a distance of more than 10 cm without loss of atoms. The atoms are delivered to the UHV chamber in a cloud with a transverse dimension of order 200 #mu#m. We discuss the extension to continuous operation of the guided atomic fountain. The 3D MOT is replaced by a funnel with 2D trapping and 3D cooling which continuously extracts the cold atoms using moving molasses. A comparison between the flux of guided atoms obtained in a pulsed fashion from the 3D MOT and continuously from the funnel indicate that the pulsed case is a factor of ten more efficient. The difference is due to inferior loading from the funnel. The optically guided fountain is used to load an optical dipole trap in the UHV chamber, using an 'optical trap door'. No additional cooling is required. The dynamics of the atoms in the optical dipole trap are studied. We discuss multiple loading of a conservative trap with the view of accumulating more atoms than can be obtained in a MOT. (author)
Summary form only given. We report optical guiding of cold atoms in a free-propagating far-detuned laser beam. The atoms are initially cooled and collected in a magneto-optical trap (MOT), which typically contains over 10/sup 8/ atoms in a cigar shaped cloud with an aspect ratio of 4. Approximately 20% of these atoms are loaded into a far-detuned optical dipole beam aligned vertically through the MOT. The number loaded is limited primarily by geometrical overlap. Both guided and unguided atoms are launched with a velocity of 1.25 m/s and a temperature of 20 /spl mu/K. The guided beam is focused through a 1 mm aperture, 6 cm above the MOT, which connects the vapour cell to a UHV chamber. Atoms can be launched within the guide without heating and guided into a UHV chamber with 100% efficiency. In continuous operation, the scheme allows extraction of atoms from a MOT without loss of phase space density.
This thesis reports on the generation of MOT for laser cooling and trapping of Rubidium 87 atoms. Probe-pump technique have been used in Rb gas cell and doppler free absorption peaks has been observed. Peak at the crossover frequency will be locked for laser cooling and repump beams. This locked freuqency used in MOT to trap Rb atoms. The technique of optical molasses is used to cool the atoms and quadrupole magnetic field applied to confine or trap atoms at the center of MOT. Two chambers are constructed for 2D and 3D MOT with different pressure. Rb atoms loaded efficiently from the high flux cold atom beam generated in a compact 2D MOT. This is the first step of Bose Einstein Condensate (BEC). A performance of 2D MOT was tested by another main chamber of 3D MOT contains 3 pairs of counter-propagating beams. Over 5x10⁶ atoms trapped in a 3D MOT with loading rate of 1:8x10⁶ atoms/sec. This experiment provided an excellent starting point for future experiment on Rydberg atoms in dense ultracold quantum gases.
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.
The size of alkali vapour Bose-Einstein condensates is determined by the number of atoms which can be collected in a magneto-optical trap. This number is limited by processes involving near-resonant light. A possible technique to exceed the number limit is to load a conservative trap which is spatially separated from the laser cooling region. Here we report on an experiment where cold atoms are transferred from a magneto-optical trap to a spatially separated magnetic trap using an optically guided atomic fountain. This technique offers efficient transfer without requiring any near-resonant light. The extension to multiple and continuous loading is discussed, and we conclude that loading a spatially separated conservative trap offers a promising route towards steady-state Bose-Einstein condensation.
The primary purpose of this study is to investigate the influence of the vertical guiding laser beam waist on cold atom guiding efficiency. In this study, a double magneto-optical trap (MOT) apparatus is used. With an unbalanced force in the horizontal direction, a cold atomic beam is generated by the first MOT. The cold atoms enter the second chamber and are then re-trapped and cooled by the second MOT. By releasing a second atom cloud, the process of transferring the cold atoms from MOT to the dipole trap, which is formed by a red-detuned converged 1064-nm laser, is experimentally demonstrated. And after releasing for 20 ms, the atom cloud is guided to a distance of approximately 3 mm. As indicated by the results, the guiding efficiency depends strongly on the laser beam waist; the efficiency reaches a maximum when the waist radius (w0) of the laser is in the range of 15 to 25 μm, while the initial atom cloud has a radius of 133 μm. Additionally, the properties of the atoms inside the dipole potential trap, such as the distribution profile and lifetime, are deduced from the fluorescence images.
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.