Method and apparatus providing a difference signal indicative of radiation absorption in a magnetometer

Claim 2

In a method of measuring the intensity of minute magnetic fields with an optical absorption magnetometer having a source for the emission of radiation including radiation of a particular wavelength comprising directing a first portion of said emitted radiation of said particular wavelength through a radiation absorption cell, in which radiation of said particular wavelength is absorbed, and upon a first detector responsive to radiation of said particular wavelength to produce an output from said first detector proportional to the intensity of impinging radiation of said particular wavelength, and subjecting said radiation absorption cell to a radiofrequency magnetic field, the improvement of directing a second portion of emitted radiation of said particular wavelength upon a second and similar detector to produce an output from said second detector proportional to the intensity of impinging radiation of said particular wavelength from said source, balancing the output of said first detector against the output of said second detector to produce a difference signal, said difference signal being an improved measure of the magnetometer resonance, and controlling the frequency of said radio frequency magnetic field by feedback of said difference signal so as to achieve maximum absorption of said particular wavelength.

Claim 3

The improvement of claim 1 where said optical absorption magnetometer is a helium magnetometer.

Claim 4

In a device for measuring the strength of a magnetic field comprising a contained body of gas selected from the group consisting of alkali metals and helium, the atoms of which are acted upon by said magnetic field when in the presence thereof, means to excite the body of gas for continuously producing metastable atoms, a source of resonance radiation including radiation of a particular wavelength impinging upon and interacting with the body of gas for producing alignment of said metastable atoms contained therein, means to create and direct into the body of gas a radiofrequency magnetic field of such frequency as to diminish the alignment of metastable atoms contained in the body of gas including a variable frequency oscillator, and means to measure changes in the amount of resonance radiation of said particular wavelength absorbed by said metastable atoms including radiation detector means sensitive to said particular wavelength, the improvement wherein said source of resonance radiation directs radiation along two paths, one said path being through said body of gas and the second said path bypassing said body of gas, said radiation detector means including two separate detectors each sensitive to said particular wavelength, one said detector producing an output proportional to the intensity of the resonance radiation of said particular wavelength reaching that one said detector via said one path and the second said detector producing an output proportional to the intensity of the resonance radiation of said particular wavelength reaching that second said detector via said second path, and including means for balancing the outputs from said first and second detectors to produce a difference signal, means for connecting said difference signal as an input to said variable frequency oscillator to vary the output frequency thereof and obtain maximum absorption of radiation of said particular wavelength, and means for measuring the frequency at which maximum absorption of radiation of said particular wavelength is obtained as a measure Of the magnetic field surrounding said body of gas.

Claim 5

In a device for measuring the strength of a magnetic field comprising a contained body of gas selected from the group consisting of alkali metals and helium, the atoms of which are acted upon by said magnetic field when in the presence thereof, means to excite the body of gas for continuously producing metastable atoms, a source of resonance radiation including radiation of a particular wavelength impinging upon and interacting with the body of gas for producing alignment of said metastable atoms contained therein, means to create and direct into the body of gas a radiofrequency magnetic field of such frequency as to diminish the alignment of metastable atoms contained in the body of gas including a variable frequency oscillator, and means to measure changes in the amount of resonance radiation of said particular wavelength absorbed by said metastable atoms including radiation detector means sensitive to said particular wavelength, the improvement wherein said source of resonance radiation directs radiation along two paths, one said path being through said body of gas and the second said path bypassing said body of gas, said radiation detector means including two separate detectors each sensitive to said particular wavelength, one said detector producing an output proportional to the intensity of the resonance radiation of said particular wavelength reaching that one said detector via said one path and the second said detector producing an output proportional to the intensity of the resonance radiation of said particular wavelength reaching that second said detector via said second path, and including means for balancing the outputs from said first and second detectors to produce a difference signal, means for connecting said difference signal as an input to said variable frequency oscillator to vary the output frequency thereof and obtain maximum absorption of radiation of said particular wavelength, and means for measuring the frequency at which maximum absorption of radiation of said particular wavelength is obtained as a measure Of the magnetic field surrounding said body of gas.

Claim 6

The improvement of claim 3 where said contained body of gas is helium.