Narrow Line Rubidium Magnetometer for High Accuracy Field Measurements

Observations of Zeeman tansitions in Rb87 vapor can be used to make accurate measurements of the earth's magnetic field provided that the resonance lines are narrow enough so that the separate components of the transitions are resolved. However, the resulting relatively low signal-to-noise ratio makes it difficult to follow rapid chages in the field. Self-oscillating magnetometers have rapid response to magnetic field changes and high sensitivity, but poor long-term stability. The advantages of both approaches can be obtained with a compound magnetometer in which a self-oscillating magnetometer is locked with a long time constant to a narrow and well-resolved Zeeman transition. We designed and built two prototype optically pumped Rb87 magnetometers of this kind, and carried out a stability test on them. Half-hour means of the magnetic field difference between the two were obtained for a period of nine and a half days. During this time local magnetic field activity ranged from quiet to disturbed and a sudden commencement occurred. The standard deviation of the individual half-hour difference