Atomic magnetometer and method of sensing magnetic fields

• US 8,334,690 B2
• Filed: 08/07/2009
• Issued: 12/18/2012
• Est. Priority Date: 08/07/2009
• Status: Active Grant

• Current Assignee: National Institute of Standards and Technology (Government of the United States of America)
• Original Assignee: The United States of America As Represented By The Secretary of Commerce
• Inventors: Kitching, John, Knappe, Svenja, Preusser, Jan, Gerginov, Vladislav
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): Fetzner, Tiffany
• Application Number:
  US12/537,922
• Publication Number:
  US 20110031969A1
• Time in Patent Office: 1,229 Days
• Field of Search: 324300-322, 324/464.4, 324/244.1, 600407-435, 382128-131
• US Class Current: 324/301
• CPC Class Codes: G01R 33/0286 comprising microelectromechanical systems [MEMS] MEMS devices in general B81B
• CPC Class Codes: G01R 33/032 using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
• CPC Class Codes: G01R 33/26 using optical pumping

Abstract

A magnetometer and method of use is presently disclosed. The magnetometer has at least one sensor void of extraneous metallic components, electrical contacts and electrically conducting pathways. The sensor contains an active material vapor, such as an alkali vapor, that alters at least one measurable parameter of light passing therethrough, when in a magnetic field. The sensor may have an absorptive material configured to absorb laser light and thereby activate or heat the active material vapor.

Claims

1. A magnetometer comprising:

at least one sensor comprising;

an alkali material;

an alkali vapor cell that is void of electrical contacts and void of electrically conducting pathways and configured to contain said alkali material and vapor of said alkali material and configured to heat said alkali material to a desired temperature with laser light, said alkali vapor cell comprising;

at least one translucent or transparent wall configured to allow laser light to pass therethrough;

at least one reflective, refractive or transmissive wall configured to reflect, refract or transmit at least a portion of laser light passing through said at least one translucent or transparent wall to a detector;

a material configured to interact with laser light and thereby heat said alkali material to a desired temperature and evolve a sufficient amount of alkali vapor from said alkali material, within said alkali vapor cell; and

said sufficient amount of alkali vapor being suitable to alter at least one measurable parameter of laser light in response to a magnetic field;

said magnetometer further comprising;

at least one laser configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall; and

a detector configured to receive laser light after passing through said alkali vapor.

2. The magnetometer of claim 1 comprising a first laser and a second laser;

said first laser being configured to heat said material configured to interact with laser light by directing laser light onto said material, thereby absorbing laser light and thereby heating said alkali material; and

said second laser being configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall.

3. The magnetometer of claim 1 comprising

a single laser configured to heat said material configured to interact with laser light by directing laser light onto said material, thereby absorbing laser light and heating said alkali material, and

the single laser being configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall.

4. The magnetometer of claim 1 comprising

a first laser configured to desorb alkali atoms from a material surface and

a second laser being configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall.

5. The magnetometer of claim 1 further comprising the limitations of a) or b):

a) wherein said at least one reflective, refractive or transmissive wall is configured to direct light emitted from said at least one laser toward a different location than a location of said at least one laser; and

wherein said at least one laser and said detector are positioned in different locations;

b) wherein said at least one reflective, refractive or transmissive wall is configured to direct light received from said at least one laser at a direction proximately opposite a direction of light emitted from said at least one laser; and

wherein said at least one laser and said detector are positioned in proximate locations.

6. The magnetometer of claim 1 wherein said at least one reflective, refractive or transmissive wall comprises at least one corner cube reflector.

7. The magnetometer of claim 1 wherein said alkali vapor cell further comprises:

at least one wall comprising said material configured to interact with laser light and configured to heat said alkali material to a desired temperature.

8. The magnetometer of claim 7 wherein said at least one wall comprising said material configured to interact with laser light comprises a coating of absorptive material.

9. The magnetometer of claim 1 wherein said at least one laser configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall comprises a single laser configured to orient the atoms of said alkali vapor and provide said laser light emitted to said detector in order to measure the effects of the magnetic field on the atom orientation.

10. The magnetometer of claim 1 wherein said at least one laser configured to direct laser light into said alkali vapor cell through said at least one translucent or transparent wall comprises a first and a second laser;

said first laser being configured to orient or align the atoms of said alkali vapor;

said second laser being configured to provide said laser light toward said detector in order to measure the effects of the magnetic field on the atom orientation or the atom alignment.

11. The magnetometer of claim 1 comprising an array of said sensors wherein each sensor in said array of sensors is positioned at a different location, each sensor in said array of sensors is configured to substantially simultaneously measure said magnetic field, while providing data for at least one of a), b), and c):

a) identifying the location of a source of said magnetic field;

b) removing the effects of a spatially uniform but time varying magnetic field; and

c) removing the effects of higher order spatial nonuniformities of the magnetic field which vary in time.

12. The magnetometer of claim 1 wherein said at least one translucent or transparent wall is a wavelength-dependent optical filter comprising said material configured to interact with laser light and configured to heat said alkali material to a desired temperature.

13. The magnetometer of claim 1 wherein said sensor is fabricated using micromachining processes.

14. A method for detecting a magnetic field comprising the steps of:

directing a first beam of laser light to a magnetic sensor;

heating an alkali material, contained within said magnetic sensor, to a desired temperature with said first beam of laser light;

vaporizing at least a portion of said alkali material within said magnetic sensor at the desired temperature;

containing said alkali material vapor within said magnetic sensor;

passing a second beam of laser light through said alkali material vapor;

receiving said second beam, with a detector, after said second beam of laser light has passed through said alkali material vapor; and

detecting, with said detector, at least one measurable parameter of said second beam that is altered upon said second beam passing through said alkali material vapor when said magnetic sensor is in the presence of a magnetic field.

15. The method for detecting a magnetic field of claim 14 wherein said steps of heating an alkali material;

vaporizing at least a portion of said alkali material within said magnetic sensor;

containing said alkali material vapor within said magnetic sensor; and

passing a second beam of laser light through said alkali material vapor are each carried out in an environment with a magnetic field being present and said step of vaporizing at least a portion of said alkali material within said magnetic sensor produces an alkali material vapor density within said magnetic sensor which suppresses spin-exchange collisions of the alkali material vapor.

16. The method for detecting a magnetic field of claim 14 wherein measuring a precession of the alkali atoms about a static magnetic field is accomplished through a modulation of the frequency of amplitude of the laser light incident on an atomic sample during said step of passing a second beam of laser light through said alkali material vapor.

17. A magnetometer comprising:

at least one sensor head that is void of any electrical contacts, void of any electrically conducting pathways, and extraneous metallic components, said at least one sensor head comprising;

an alkali material;

an alkali vapor cell containing said alkali material and vapor of said alkali material;

said alkali vapor cell comprising a material configured to heat said alkali material contained therein to a desired temperature with laser light in order to vaporize a portion of said alkali material upon the application of laser light onto or through an outer surface thereof; and

an enclosure configured to substantially enclose and insulate said alkali vapor cell; and

an alkali vapor cell support, comprising a low thermal conductive material, configured to support said alkali vapor cell within said enclosure wherein a void space is between said outer surface of said alkali vapor cell and said enclosure;

said magnetometer further comprising;

a first optic fiber comprising a first end in light communication with said alkali vapor cell;

a laser in light communication with a second end of said first optic fiber;

a second optic fiber having a first end in light communication with said alkali vapor cell; and

an optical detector in light communication with a second end of said second optic fiber, said optical detector being configured to detect at least one measurable parameter of laser light that is altered upon passing through said sensor head when in the presence of a magnetic field.

18. The magnetometer of claim 17 further comprising

one or more lenses configured to collimate or refocus light emitted from said alkali vapor cell and

transmit said collimated or refocused light into said first end of said second optic fiber.

19. The magnetometer of claim 17 further comprising the limitation of a) or b);

a) wherein said first optic fiber is a polarization-maintaining fiber;

b) wherein said first or second optic fiber is a multi-mode fiber.

20. The magnetometer of claim 17 wherein said first optic fiber is configured to direct light of different wavelengths toward said alkali vapor cell, said alkali vapor cell further comprising:

a wavelength-dependent optical filter configured to receive light transmitted thereto through said first optic fiber, and said wavelength-dependent optical filter further comprises;

said material configured to heat said alkali material contained therein.