# US 2021/0243877 A1 · Continuous, Velocity-Controlled Three-Dimensionally Laser-Cooled Atom Beam Source with Low Fluorescence

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- Number: US 2021/0243877 A1
- Document ID: US20210243877A1
- Status: Published application
- Kind: A1
- Application number: 17/160,564
- Filed: 2021-01-28
- Published: 2021-08-05
- Earliest claimed: 2020-01-31
- Assignees: The Government of the United States of America, as represented by the Secretary of the Navy
- Applicants: The Government of the United States of America, as represented by the Secretary of the Navy
- Inventors: Adam Black; Mark Bashkansky; Charles Fancher; Jonathan Kwolek
- Web page: https://patentgrep.com/patent/US20210243877A1

## CPC

- H05H 3/02: Molecular or atomic-beam generation, e.g. resonant beam generation
- G02B 27/283: {used for beam splitting or combining}
- H01S 3/0071: {Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction}
- H05H: PLASMA TECHNIQUE (apparatus or processes specially adapted for producing X-rays H05G2/00); PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

Method and apparatus for producing a cooled atom beam suitable for use applications requiring cold atoms. A two-stage cooling process is employed in which the atoms in the atom beam are cooled in two, spatially separated regions of a cooling apparatus, wherein the atoms are first cooled in two dimensions by two counterpropagating laser beams under a magnetic field and then are cooled in three dimensions by means of an optical molasses, where the power, frequency, and magnetic fields are tuned to obtain a continuous beam of three-dimensionally cooled atoms having a controllable velocity distribution, very low decoherence, and low background atomic gas loss.

## Claims

### Claim 1

A method for forming a continuous, velocity-controlled three-dimensionally laser-cooled atom beam, comprising:
providing a vacuum enclosure comprising a first laser-cooling region joined via an aperture with a second laser-cooling region, a longitudinal axis of the second laser-cooling region being offset at an angle relative to a longitudinal axis of the first laser-cooling region;
providing an atom vapor in the first laser-cooling region;
directing a first set of counterpropagating laser beams into the atom vapor in the first laser-cooling region under an applied magnetic field, the first set of counterpropagating laser beams comprising two pairs of beams offset from one another by a first predetermined angle, the first set of laser beams and the magnetic field forming a two-dimensional magneto-optical trap (2D+ MOT) that causes the atom vapor to form an initial transversely cooled atom beam traveling through the first laser-cooling region, through the aperture, and into the second laser-cooling region; and
directing a second set of counterpropagating laser beams into the transversely cooled atom beam in the second laser-cooling region, the second set of counterpropagating laser beams comprising a first pair of counterpropagating beams traveling along a z+/z− axis and further comprising a second and third pair of counterpropagating beams propagating in an x-y plane, the second and third pair of counterpropagating beams being separated from one another by a second predetermined angle, the second set of counterpropagating laser beams forming a three-dimensional optical molasses (3D OM);
each of the beams forming the 2D+ MOT and each of the beams forming the 3D OM having a corresponding wavelength, the wavelength of each beam having a predetermined difference from a resonance frequency of the atoms in the atom vapor, all of the beams forming the 2D+ MOT and the 3D OM being fired simultaneously and continuously as the atoms travel through the enclosure; and
wherein the 3D OM beams cool the initial transversely cooled atom beam in three dimensions to a predetermined sub-Doppler temperature and to a predetermined mean velocity as it travels through the second laser-cooling region to continuously produce a velocity-controlled three-dimensionally cooled low-fluorescence atom beam.

### Claim 2 (depends on 1)

The method according to claim 1, further comprising applying an initial laser push beam to the atom vapor to increase the atom flux in the first laser-cooling region.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the wavelengths of the beams forming the 2D+MOT have a frequency detuning from a resonant frequency of the atoms in the atom vapor between −2Γ0 and −1/2Γ0 and the wavelengths of the beams forming the 3D OM each have a corresponding mean frequency detuning from the resonant frequency of the atoms in the atom vapor between −10Γ0 and −2Γ0, where Γ0 is a natural linewidth of a cooling resonance of the atoms in the atom vapor.

### Claim 4 (depends on 1)

The method according to claim 1, further comprising applying a repump beam to the atoms as they travel through the first and second laser-cooling regions to ensure that the atoms maintain an energy level that permits cooling of the atoms to occur.

### Claim 5

An apparatus for forming a continuous, velocity-controlled three-dimensionally laser-cooled atom beam, comprising:
a two-stage vacuum enclosure comprising a first laser-cooling region and a second laser-cooling region joined to the first laser-cooling region via an intermediate region that is opaque to a wavelength of laser beams in the first laser-cooling region, the intermediate region having an aperture formed therein to join with the second laser-cooling region, a longitudinal axis of the second laser-cooling region being offset from a longitudinal axis of the first laser-cooing region; the first laser-cooling region including at least one magnetic element configured to apply a magnetic field to atoms in the first laser-cooling region;
first laser sources that direct a first set of counterpropagating laser beams comprising two beams offset from one another by a predetermined angle into atoms in the first laser-cooling region in the presence of the magnetic field, the first set of counterpropagating beams and the magnetic field forming a two-dimensional magneto-optical trap (2D+ MOT) that transversely cools the atoms in the first laser-cooling region and causes them to form an atom beam that travels into the second laser-cooling region via the aperture; and
second laser sources that apply a second set of counterpropagating laser beams to the atom beam in the second laser-cooling region, the second set of counterpropagating laser beams comprising a first pair of counterpropagating beams traveling along a z+/z− axis and further comprising a second and third pair of counterpropagating beams propagating in an x-y plane, the second and third pair of counterpropagating beams being separated from one another by a second predetermined angle, the second set of counterpropagating laser beams forming a three-dimensional optical molasses (3D OM) in the second laser-cooling region;
wherein the first set of beams forming the 2D+ MOT and the second set of beams forming the 3D OM all are fired simultaneously and continuously as the atoms travel through the enclosure;
wherein each of the beams forming the 2D+ MOT and each of the beams forming the 3D OM has a corresponding wavelength, the wavelength of each beam having a predetermined difference from a resonance frequency of the atoms in the atom vapor, all of the beams forming the 2D+ MOT and the 3D OM being fired simultaneously and continuously as the atoms travel through the enclosure; and
wherein the 3D OM beams cool the initial transversely cooled atom beam in three dimensions to a predetermined sub-Doppler temperature and to a predetermined mean velocity as it travels through the second laser-cooling region to continuously produce a velocity-controlled three-dimensionally cooled low-fluorescence atom beam.

### Claim 6 (depends on 5)

The apparatus according to claim 5, wherein the wavelengths of the beams forming the 2D+ MOT have a frequency detuning from a resonant frequency of the atoms in the atom vapor between −2Γ0 and −1/2Γ0 and the wavelengths of the beams forming the 3D OM each have a corresponding mean frequency detuning from the resonant frequency of the atoms in the atom vapor between −10Γ0 and −2Γ0, where Γ0 is a natural linewidth of a cooling resonance of the atoms in the atom vapor.