Nuclear magnetic resonance probe system

A method for measuring an external magnetic field in a nuclear magnetic resonance system, the method comprising:

• generating an optical pump beam at a first wavelength corresponding to one of a D1 emission line and a D2 emission line associated with an alkali metal vapor via a pump laser;
• generating an optical probe beam at a second wavelength corresponding to the other of the D1 emission line and the D2 emission line associated with the alkali metal vapor via a probe laser;
• splitting the optical probe beam into a first portion and a second portion;
• combining the first portion of the optical probe beam with the optical pump beam to provide a combined beam, such that the combined beam comprises the first portion of the optical probe beam that is substantially collinear with the optical pump beam;
• directing the combined beam and the second portion of the optical probe beam along orthogonal axes through a sensor cell comprising the alkali metal vapor;
• filtering light having the first wavelength to pass light having the second wavelength to a photodetector assembly;
• measuring a Faraday rotation associated with the second portion of the optical probe beam leaving the sensor cell via the photodetector assembly, the Faraday rotation being associated with the external magnetic field;
• measuring a Faraday rotation associated with the first portion of the optical probe beam exiting the sensor cell;
• and
• adjusting at least one parameter of the nuclear magnetic resonance system based on the Faraday rotation of the first portion of the optical probe beam to substantially stabilize an internal magnetic field associated with the alkali metal vapor in the sensor cell.

A nuclear magnetic resonance (NMR) sensor system comprising:

• a sensor cell comprising an alkali metal vapor;
• a pump laser configured to generate an optical pump beam at a first wavelength corresponding to one of a D1 emission line and a D2 emission line associated with the alkali metal vapor;
• a probe laser configured to generate an optical probe beam at a second wavelength corresponding to the other of the D1 emission line and the D2 emission line associated with the alkali metal vapor;
• beam optics comprising:
• a linear polarizer and a quarter-wave plate configured to convert the optical pump beam to a circular polarization;
• a linear polarizer configured to convert the optical probe beam to a linear polarization;
• and
• additional optics configured to direct the optical pump beam and the optical probe beam along orthogonal axes through the sensor cell;
• and
• detection optics comprising a photodetector assembly configured to measure a Faraday rotation associated with the optical probe beam leaving the sensor cell for measurement of a polarization vector of the alkali metal vapor, the detection optics comprising at least one filter configured to filter light having the first wavelength and to pass light having the second wavelength to the photodetector assembly;
• wherein the probe laser is a first probe laser configured to generate a first optical probe beam, and wherein the photodetector assembly is a first photodetector assembly, the system further comprising a second probe laser configured to generate a second optical probe beam at the first wavelength and at an intensity that is approximately twice an intensity of the first optical probe beam, the second optical probe beam being provided in an optical path that is collinear with and counter-propagating with respect to the first optical probe beam.