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Continuous-Wave Atom Laser

Continuous injection and propagation of a cold atomic beam has been demonstrated.

Progress has been made toward realization of a continuous-wave, phase-andamplitude- stable atom laser based on magnetic guiding, magnetic compression, and continuous distributed evaporative cooling of a sparse cloud of 87Rb atoms. This apparatus is intended to serve as a prototype of sources of coherent matter waves for future atom-interferometric field and motion sensors.

A major part of the apparatus is a magnetic guide comprising two hollow, watercooled, 3.175-mm-diameter wires (see figure) about 1.7 m long in a vacuum chamber in which the 87Rb atoms are manipulated. In operation, the wires are excited with parallel direct currents of 300 A, thereby generating a two-dimensional quadrupole magnetic field having a minimum magnitude along the central longitudinal axis of the guide with large lateral gradient. The 87Rb atoms used in this apparatus are prepared in the ⎜F = 1, mF = -1〉 quantum state in which the atoms have magnetic moments that cause them to be attracted to the locus of minimum magnitude of the magnetic field — that is, to the central longitudinal axis.

The Magnetic Guide is an essential component of the CW atom laser. The magnetic-field plot was calculated for a center-to-center distance of 5 mm between the hollow wires and a current of 300 A in each wire (in the same direction in both wires). The field contour lines are separated by intervals of 20 G.
In a 0.2-m-long section of the guide at the input end, the wires are oriented vertically and start with a center-to-center distance of about 3.7 cm at the point where the 87Rb atoms are injected. The center-tocenter distance tapers down to 5.17 mm at the upper end of this section, where there is a bend to a horizontal orientation. The distance remains constant through the bend, then tapers along the 1.5-m-long horizontal section, to a minimum of 4.175 mm at the output end. The gradient of the magnitude of the magnetic field is about 20 G/cm at the input end and, by virtue of the aforementioned tapers, increases to 1.7 kG/cm in the bend, then gradually increases after the bend to a maximum of 2.7 kG at the output end. A crucial benefit of the increase in the gradient along the guide is that the atomic distribution becomes magnetically compressed in the transverse directions as the atoms propagate toward the output end. The compression increases the rate of collisions between atoms, thus facilitating evaporative cooling. Moreover, by use of an alternating current of frequency v coupled directly into the guide wires, atoms exceeding a transverse kinetic energy of hv (where h is Planck's constant) have been continuously and selectively removed from the atomic beam.

At the input end, 87Rb atoms are injected continuously into the guide in a side-loading scheme that involves a sequence of two modified magneto-optical traps. An open-channel imaging method enables measurement of temperatures and flux of the beam of atoms in the guide under steady-state conditions. At the stage of development at this writing, the beam in the high-gradient portion of the guide has been found to have a transverse temperature of 420 ±40 μK, a longitudinal temperature of 1 mK, an average speed of order 1 m/s, and an atom flux of about 3×107.

It is planned to incorporate a potential well into the guide near the output end, for the purpose of forming a continuous-wave (CW) Bose-Einstein condensate in the well. It is further planned to utilize quantum-mechanical tunneling to extract a coherent CW matter wave from the BEC. A Zeeman slower (a device that utilizes laser cooling and the Zeeman effect to reduce speeds of atoms) has been constructed, with the intent to eventually use it to enable highflux operation of the guide. High flux is essential to further progress toward achieving CW evaporative cooling of the beam, a CW BEC, and CW atom lasing.

This work was done by Georg Raithel of the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Photonics category. ARL-0003

Topics:
Electrical systems Forming Imaging and visualization Lasers Logistics Magnetic materials Manufacturing processes Optics Photonics Research and development Starters and starting
This Brief includes a Technical Support Package (TSP).
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Continuous-Wave Atom Laser

(reference ARL-0003) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the April, 2007 issue of Defense Tech Briefs Magazine (Vol. 1 No. 2).

    Read more articles from the archives here.

    Overview

    The document is a final progress report on a research project led by Georg Raithel at the University of Michigan, focusing on the development of a continuous-wave (cw) atom laser. The project aims to create a phase- and amplitude-stable atom laser using techniques such as magnetic guiding, magnetic compression, and continuous distributed evaporative cooling.

    Key achievements of the project include the successful demonstration of continuous operation of a cold atomic beam within a high-gradient magnetic guide, which has a length of 1.7 meters and a gradient of up to 2.7 kG/cm. The research team developed an imaging method that allows for in-situ measurements of atom temperatures and fluxes, which are critical for understanding the behavior of the atomic beam.

    The report highlights specific measurements obtained during the experiments. The transverse temperature of the atomic beam was found to be 420 micro-Kelvin, while the longitudinal temperature was measured at 1 mK. The average velocity of the atoms in the guide was approximately 1 m/s, and the atomic flux was determined to be about 3 × 10^7 atoms per second. These measurements are essential for evaluating the performance of the atom laser and its potential applications.

    To enhance the efficiency of evaporative cooling, the project included the construction of a Zeeman slower, which is designed to enable atom fluxes exceeding 10^9 atoms per second. This level of flux is necessary for effective evaporative cooling, which is a crucial step in achieving Bose-Einstein condensation and creating a coherent matter-wave beam.

    The report emphasizes the importance of these advancements in the context of future applications, particularly in the field of atom interferometry. The development of a cw atom laser could lead to significant improvements in sensing and navigation technologies, making it a valuable contribution to the field of atomic physics.

    Overall, the document outlines the progress made in the project, detailing the experimental setup, methodologies, and results obtained, while also discussing the implications of this research for future technological advancements in atom-based applications.

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