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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Single-laser, one-beam, tetrahedral magneto-optical trap

Matthieu Vangeleyn, Paul F. Griffin, Ian A. McGregor, Erling Riis, Aidan S. Arnold

Published Jun 1, 2009• 2 citations

Abstract

Shimizu et al. demonstrated an alternative of the usual six beam magneto-optical trap (MOT), using four independent beams in a tetrahedral configuration. This paper demonstrates a novel version of the four beam MOT using a triplet of mirrors to split and steer an incoming beam into three parts such that all four beams cross in the correct configuration. In the usual pyramid configuration, the MOT forms below the top surface of the pyramid and the absence of optical access strongly reduces any manipulation of the cold atomic cloud. In addition, a micro-fabricated tetrahedral configuration offers an ideal tool for a high phase stability optical lattice, with the benefit of fixed lattice geometry. In the demonstration setup, the triplet is positioned underneath the quartz vacuum chamber and its thickness had to be considered. Therefore, the angle of the mirrors is slightly more acute than in the ideal situation, resulting in 45Adeg beams, in order to form the MOT above the plate. Moreover, irect modulation of the diode current by a frequency corresponding to the alkali atom energy splitting in order to generate the repumping light is used. The setup was used to cool down87Rb atoms via the F = 2 and F' = 3 energy levels of the D2 transition line. With the traditional cooling/repump lasers, 1.3 x 106atoms were trapped. With a 10mW microwave source, we generated enough repump light into the laser to get 1.1 x 106atoms, that is 85% compared to the two laser setup.

DOI: 10.1109/cleoe-eqec.2009.5192426

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Shimizu et al. demonstrated an alternative of the usual six beam magneto-optical trap (MOT), using four independent beams in a tetrahedral configuration. This paper demonstrates a novel version of the four beam MOT using a triplet of mirrors to split and steer an incoming beam into three parts such that all four beams cross in the correct configuration. In the usual pyramid configuration, the MOT forms below the top surface of the pyramid and the absence of optical access strongly reduces any manipulation of the cold atomic cloud. In addition, a micro-fabricated tetrahedral configuration offers an ideal tool for a high phase stability optical lattice, with the benefit of fixed lattice geometry. In the demonstration setup, the triplet is positioned underneath the quartz vacuum chamber and its thickness had to be considered. Therefore, the angle of the mirrors is slightly more acute than in the ideal situation, resulting in 45Adeg beams, in order to form the MOT above the plate. Moreover, irect modulation of the diode current by a frequency corresponding to the alkali atom energy splitting in order to generate the repumping light is used. The setup was used to cool down87Rb atoms via the F = 2 and F' = 3 energy levels of the D2 transition line. With the traditional cooling/repump lasers, 1.3 x 106atoms were trapped. With a 10mW microwave source, we generated enough repump light into the laser to get 1.1 x 106atoms, that is 85% compared to the two laser setup.

We have realized a 4-beam pyramidal magneto-optical trap ideally suited for future microfabrication. Three mirrors split and steer a single incoming beam into a tripod of reflected beams, allowing trapping in the four-beam overlap volume. We discuss the influence of mirror angle on cooling and trapping, finding optimum efficiency in a tetrahedral configuration. We demonstrate the technique using an ex-vacuo mirror system to illustrate the previously inaccessible supra-plane pyramid MOT configuration. Unlike standard pyramidal MOTs both the pyramid apex and its mirror angle are non-critical and our MOT offers improved molasses free from atomic shadows in the laser beams. The MOT scheme naturally extends to a 2-beam refractive version with high optical access. For quantum gas experiments, the mirror system could also be used for a stable 3D tetrahedral optical lattice.

We present a novel and simple magneto-optical trap in pyramidal and in conical hollow mirrors, using a single beam. A diode laser having modulation sidebands at microwaves is used for cooling, trapping, and repumping of rubidium atoms in a vapor cell. When the laser is circularly polarized and sent into the hollow region, three pairs of counterpropagating beams are automatically produced therein that have the same polarization configuration as that of a conventional six-beam magneto-optical trap. The fluorescence by the trapped atoms and its mirror image are observed simultaneously. This system may be useful for atom-manipulation applications such as gravitational atom traps and atom waveguides.

A three-dimensional magneto-optical trap (MOT), acting as an efficient method for producing cold atoms from room-temperature atomic vapor, has been widely used to develop atomic sensors. Various compact MOTs using a single laser beam have been reported, simplifying apparatuses and leading to miniaturized devices. Here, we propose single-beam MOTs based on back-to-back pyramidal and conical mirrors. In such back-to-back mirrors, a MOT trapping volume is formed by an incident laser beam, a retroreflected beam, and multiple reflections from the mirror surfaces. We present the design of back-to-back mirrors and a series of compact MOT configurations, with the potential of increasing access to the MOT and simultaneously creating multiple MOTs. We demonstrate a MOT in a back-to-back conical mirror, loading \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{}

{10}^{7}

{}^{87}\mathrm{Rb}

atoms from background vapor and cooling the atoms to \ensuremath{\sim}7 \textmu{}K using polarization gradients. Single-beam MOTs based on back-to-back mirrors contribute to building compact and scalable cold-atom-based sensors.

We have used a pyramid magneto-optical trap (MOT) to create a compact source of cold rubidium atoms. The four dielectric-coated metal mirrors in vacuum are arranged in the form of a pyramid that creates the light field for a MOT from a single ingoing laser beam. The atoms are pushed out through a hole (aperture) in the apex of the pyramid, in a direction determined by the laser light, to give a flux of Rb-87 atoms greater than 2 × 10^10 per second with a mean velocity of 33 m/s (FWHM of 28 m/s) and a divergence of 58 mrad. The pyramid MOT has a unique mechanism for adjusting aperture size and it is highly suitable for portable quantum technology devices.

In cold atom physics, the complexity of traditional magneto-optical trap system limits the use of their associated instruments for field applications in atomic physics, such as gravity mapping, space navigation and deep space exploration. This study introduces a novel compact MOT design that addresses these issues by simplifying the structure and reducing the size. The height of the unit is 0.7 m, the volume is 6.3×10−2m3 and the mass is 11.32 kg. The new design utilizes a single laser to generate the two different frequencies needed for laser cooling by internally splitting the beam, shifting the frequency and then combining them, effectively controlling both the cooling and repumping beams. The compact vacuum chamber optical path, in conjunction with the magnetic field, facilitates the capture of 87Rb atoms in an ultra-high vacuum environment. Experimental results demonstrate an atom loading rate of up to 1.79×10787Rb atoms per second, confirming the system’s effectiveness in capturing and cooling 87Rb atoms. This design provides a flexible and portable solution, offering valuable insights for the advancement of compact MOT and its applications in cold atom physics.