Nd:LNA laser optical pumping of 4He: Application to space magnetometers

Abstract

We have observed Hanle signals and n=0, p=1 parametric resonances of 23S1 metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single-line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for developing ultrasensitive resonance magnetometers using single-line laser pumping.

A Compact Laser Pumped 4He Magnetometer with Laser-Frequency Stabilization by Inhomogeneous Light Shifts

“…In this paper, we propose a compact 4 He magnetometer system, which measures ambient magnetic field in the magneto-optical double-resonance (MODR) configuration and simultaneously stabilizes the laser frequency by using the inhomogeneous light shifts in the same cell. As the laser beam is absorbed by the 4 He atoms, it generates light-intensity spatial gradient along the propagation direction, resulting in inhomogeneous light shifts at different positions [21]. The inhomogeneous distribution of light shifts in the laser pumped 4 He magnetometer is analyzed theoretically and verified experimentally.…”

“…Laser pumped atomic magnetometers have been studied since the 1980s [1][2][3][4], and gradually evolved from experimental researches to practical applications [5][6][7][8]. Compared with the discharge lamp, the laser with far better monochromaticity and higher intensity can improve the signal-to-noise ratio and therefore the sensitivity of the atomic magnetometer [9][10][11][12].…”

“…Apart from using an additional reference cell, other alternative methods can also be exploited to stabilize the laser frequency. For example, the atomic alignment to the orientation-conversion (AOC) effect [19] has been used to suppress light shift in laser pumped 4 He magnetometer [9]. The saturated absorption spectroscopy and the magnetic resonance using circularly polarized light also can be implemented in the same cell [20].…”

“…The frequency stabilization scheme is based on the asymmetric line shape of magnetic resonance which is induced by spatially inhomogeneous light shifts. We investigate the asymmetric line shape of the magnetic resonance signal theoretically and experimentally in laser pumped 4 He magnetometer with the magneto-optical double-resonance configuration. Notice that, due to the asymmetric line shape, the in-phase component of the magnetic resonance signal is shown to have a linear dependence with respect to the laser frequency detuning and is used to actively lock the laser frequency to the resonant point.…”

Planetary Magnetic Field Measurements: Missions and Instrumentation

“…More recent developments include the use of a laser instead of the He lamp used in the original design for providing optical pumping of the helium gas in the sensor cell (Slocum et al 1988;Slocum 1991). As reported by Slocum (2002), the new design includes vector and scalar operation in the same instrument that can achieve accuracies of better than 1 part in 10,000 (better than ∼1 nT in the Earth's magnetic field) and a sensitivity of ∼0.2 pT/Hz 1/2 .…”