Pulsed scalar atomic magnetometer
Disclosed is a method and apparatus relating generally to scalar atomic magnetometers. The disclosed methods and apparatus utilize a pressurized sample chamber and a high frequency pulsed pump laser to increase spin polarization and significantly suppress heading errors. These methods and apparatus may also include alternating polarization of the pump light between pulses.
1. A magnetometer, comprising:
a sample chamber;
a sample medium within the sample chamber, the sample medium comprising an alkali metal vapor and a quenching gas at a pressure greater than 100 torr that enables spin polarization of alkali metal atoms to be greater than or equal to a predetermined level; and
a pump laser having output directed towards the sample chamber, the laser having an intensity sufficiently high to polarize to a predetermined level in a period of time shorter than the Larmor precession period.
2. The magnetometer of claim 1 , wherein the predetermined level is 95% or greater.
3. The magnetometer of claim 1 , wherein the sample is optically thick.
4. The magnetometer of claim 3 , wherein the laser can propagate at least three optical lengths into the sample medium.
5. The magnetometer of claim 1 , further comprising a probe laser configured to produce a probe light directed towards the sample chamber.
6. The magnetometer of claim 5 , wherein at least a portion of the pump light and at least a portion of the probe light are collinear.
7. The magnetometer of claim 1 , wherein the pump laser is adapted to alternate the polarization of the pump laser between successive pulses.
8. The magnetometer of claim 1 , wherein the plurality of pulses are produced at a rate synchronous with repetitive magnetic field noise.
9. The magnetometer of claim 8 , wherein the rate is selected from the group consisting of 16.7 Hz, 25 Hz, 50 Hz, 60 Hz, and 400 Hz.
10. The magnetometer of claim 1 , wherein the pump laser is adapted to produce a plurality of pulses of at least one of o + or o − pump light.
11. A method for using a magnetometer to reduce heading error, comprising the steps of:
providing a magnetometer according to claim 1 ;
optically pumping alkali metal atoms using pulses of at least one of o + or o − pump light, the duration of each pulse being shorter than the Larmor period and the intensity of each pulse is sufficient to polarize atoms to a predetermined level of polarization; and
monitoring precession of spin of the alkali metal atoms with a probe laser and a detector for a period of time, the detector generating a detector signal, the detector signal having reduced heading error.
12. The method of claim 11 , wherein the predetermined level is 95% or greater.
13. The method of claim 11 , further comprising passing each pulse through a sample chamber containing the alkali metal vapor, wherein the sample chamber is configured such that the pump light propagates through the alkali metal vapor a sufficient number of optical lengths so as to allow at least some purification of circular polarization.
14. The method of claim 13 , wherein the pump light propagates at least 3 optical lengths through the alkali metal vapor.
15. The method of claim 11 , wherein the pulses of at least one of o + or o − pump light is produced by alternating the polarization of the pump laser between successive pulses.
16. The method of claim 11 , further comprising generating a spin-procession signal.
17. The method of claim 16 , wherein the period of time is approximately the spin-relaxation time.
18. The method of claim 16 , further comprising determining the frequency of the spin procession signal by non-linear fitting the signal to a decaying sine wave.