Probe beam frequency stabilization in an atomic sensor system

Patent metadata

Field	Value
Publication number	US-9500725-B2
Application number	US-201313960127-A
Country	US
Kind code	B2
Filing date	Aug 6, 2013
Priority date	Aug 6, 2013
Publication date	Nov 22, 2016
Grant date	Nov 22, 2016

Abstract

An atomic sensor system includes a magnetic field generator configured to generate a magnetic field along an axis and a probe laser configured to generate an optical probe beam. Beam optics direct the optical probe beam through a sensor cell comprising an alkali metal vapor such that the optical probe beam has at least a vector component along the axis. The system also includes detection optics comprising a photodetector assembly configured to measure a Faraday rotation associated with the optical probe beam exiting the sensor cell and to generate a feedback signal based on the Faraday rotation associated with the optical probe beam exiting the sensor cell. The system further includes a laser controller configured to modulate a frequency of the optical probe beam about a center frequency and to substantially stabilize the center frequency of the optical probe beam based on the feedback signal.

First claim

What is claimed is:

1. An atomic sensor system comprising:
a magnetic field generator configured to generate a magnetic field along an axis;
a probe laser configured to generate an optical probe beam;
a pump laser configured to generate an optical pump beam along the axis;
beam optics configured to direct the optical probe beam through a sensor cell comprising an alkali metal vapor such that the optical probe beam has at least a vector component along the axis;
detection optics comprising a photodetector assembly configured to measure a Faraday rotation associated with the optical probe beam exiting the sensor cell and to generate a feedback signal based on the Faraday rotation associated with the optical probe beam exiting the sensor cell; and
a laser controller configured to modulate a frequency of the optical probe beam about a center frequency and to substantially stabilize the center frequency of the optical probe beam based on the feedback signal.

2. The system of claim 1 , wherein the beam optics comprise a beam combiner configured to combine at least a portion of the optical probe beam with the optical pump beam, such that at least a portion of the optical probe beam and the optical pump beam are provided substantially collinearly through the sensor cell along the axis.

3. The system of claim 2 , wherein the beam combiner comprises:
an optical pickoff configured to split a portion of the optical probe beam from a first optical path that passes through the sensor cell in a first axis; and
a beam combining element configured to pass the optical pump beam and to reflect the portion of the optical probe beam into a second optical path that comprises the optical pump beam and passes through the sensor cell in a second axis orthogonal to the first axis.

4. The system of claim 1 , wherein a portion of the optical probe beam is directed through the sensor cell approximately orthogonally relative to the axis, the detection optics further comprising a second photodetector assembly configured to measure at least one characteristic associated with the at least a portion of the optical probe beam exiting the sensor cell for measurement of at least one of an external magnetic field, a spin precession frequency or phase, and a rotation of the atomic sensor system about a sensitive axis.

5. The system of claim 1 , wherein the beam optics comprises:
a half-wave plate and a linear polarizer configured to convert the optical probe beam to a predetermined linear polarization;
a polarizing beam-splitter configured to pickoff a portion of the optical probe beam having the predetermined linear polarization; and
a photodetector configured to receive the portion of the optical probe beam and to generate a reference signal corresponding to a reference intensity of the optical probe beam.

6. The system of claim 1 , wherein the photodetector assembly comprises a polarizing beam-splitter, a first photodetector, and a second photodetector, wherein the polarizing beam-splitter is configured to separate the optical probe beam exiting the sensor cell into first and second orthogonal signal components, wherein the first and second photodetectors are configured to generate first and second intensity signals corresponding to the first and second orthogonal signal components, respectively, and wherein the first and second intensity signals are provided as a difference signal corresponding to the feedback signal that is indicative of the Faraday rotation of the optical probe beam exiting the sensor cell.

7. The system of claim 1 , wherein the laser controller is configured to substantially lock the center frequency of the optical probe beam at a Faraday rotation peak that is functionally related to a wavelength of the optical probe beam based on variation of the Faraday rotation as a function of the modulated frequency of the optical probe beam.

8. An NMR gyroscope system comprising the atomic sensor system of claim 1 .

9. An atomic magnetometer system comprising the atomic sensor system of claim 1 .

10. A method for stabilizing a frequency of an optical probe beam in an atomic sensor system, the method comprising:
modulating the frequency of the optical probe beam about a center frequency based on a modulation signal;
generating a magnetic field along an axis;
splitting the optical probe beam into a first portion and a second portion;
directing the first portion of the optical probe beam substantially orthogonally relative to the axis for measuring at least one of an external magnetic field, a spin precession frequency or phase, and a rotation of the atomic sensor system about a sensitive axis;
combining the second portion of the optical probe beam collinearly with an optical pump beam that is provided along the axis and which is configured to stimulate an alkali metal vapor in a sensor cell of the atomic sensor system;
measuring a Faraday rotation associated with the second portion of the optical probe beam exiting the sensor cell;
generating a feedback signal based on the Faraday rotation associated with the optical probe beam exiting the sensor cell;
demodulating the optical probe beam exiting the sensor cell based on the modulation signal; and
stabilizing the center frequency of the optical probe beam based on the feedback signal.

11. The method of claim 10 , further comprising:
providing the optical probe beam through a half-wave plate and a linear polarizer to convert the optical probe beam to a predetermined linear polarization;
picking-off a portion of the optical probe beam; and
generating a reference signal corresponding to a reference intensity of the optical probe beam based on the portion of the optical probe beam.

12. The method of claim 10 , wherein measuring the Faraday rotation comprises:
splitting the optical probe beam into a first portion and a second portion, the first and second portions having substantially orthogonal linear polarization states;
providing the first portion to a first photodetector and providing the second portion to a second photodetector; and
generating a difference signal associated with a first intensity of the first portion and a second intensity of the second portion, respectively, the difference signal corresponding to the feedback signal that is indicative of the Faraday rotation of the optical probe beam exiting the sensor cell.

13. The method of claim 10 , wherein stabilizing the center frequency of the optical probe beam comprises substantially locking the center frequency of the optical probe beam at a Faraday rotation peak that is functionally related to a wavelength of the optical probe beam based on variation of the Faraday rotation as a function of the modulated frequency of the optical probe beam.

14. A nuclear magnetic resonance (NMR) sensor system comprising:
a magnetic field generator configured to generate a magnetic field along an axis;
a pump laser configured to generate an optical pump beam along the axis through a sensor cell comprising an alkali metal vapor;
a probe laser configured to generate an optical probe beam;
beam optics configured to split the optical probe beam into a first portion and a second portion, and to direct the first portion through the sensor cell substantially orthogonally with respect to the axis;
a beam combiner configured to combine the second portion of the optical probe beam with the optical pump beam, such that the second portion of the optical probe beam and the optical pump beam are provided substantially collinearly through the sensor cell along the axis;
a first photodetector assembly configured to measure at least one characteristic

Assignees

• Bulatowicz Michael D
• Northrop Grumman Systems Corp

Inventors

• Bulatowicz Michael D

Classifications

• G01R33/26 Primary

  using optical pumping · CPC title

• G01C19/62

  with optical pumping · CPC title