Optical pumping rates in an alkali beam

Paolo Violino

Basim R. Bulos, Will Happer

Raoul Gregory Vitale

Ganghua Mei, Huang Gui-long, Xiwen Zhu +3 more

Using rate equation formalism, we got an analytic expression describing the optical pumping of an alkali atomic beam in strong magnetic fields. By comparing with the traditional description in single velocity approximation, the influence of velocity distribution in a practical alkali atomic beam on the pumping effect was quantitatively discussed. It turned out that the rate equation treatment in single velocity approximation might result in an error within twenty percent. Laser optical pumping of 7 Li atomic beam in a strong magnetic field (0.15 T) was experimentally studied, and the results are in agreement with the theory in which the velocity distribution is taken into account.

Jiancheng Fang, Tao Wang, Hong Zhang +2 more

The hybrid optical pumping atomic magnetometers have not realized its theoretical sensitivity, the optimization is critical for optimal performance. The optimizations proposed in this paper are suitable for hybrid optical pumping atomic magnetometer, which contains two alkali species. To optimize the parameters, the dynamic equations of spin evolution with two alkali species were solved, whose steady-state solution is used to optimize the parameters. The demand of the power of the pump beam is large for hybrid optical pumping. Moreover, the sensitivity of the hybrid optical pumping magnetometer increases with the increase of the power density of the pump beam. The density ratio between the two alkali species is especially important for hybrid optical pumping magnetometer. A simple expression for optimizing the density ratio is proposed in this paper, which can help to determine the mole faction of the alkali atoms in fabricating the hybrid cell before the cell is sealed. The spin-exchange rate between the two alkali species is proportional to the saturated density of the alkali vapor, which is highly dependent on the temperature of the cell. Consequently, the sensitivity of the hybrid optical pumping magnetometer is dependent on the temperature of the cell. We proposed the thermal optimization of the hybrid cell for a hybrid optical pumping magnetometer, which can improve the sensitivity especially when the power of the pump beam is low. With these optimizations, a sensitivity of approximately 5 fT/Hz(1/2) is achieved with gradiometer arrangement.

F. A. Franz