High-sensitivity helium resonance magnetometers

Abstract

A number of techniques to improve the sensitivity of helium resonance magnetometers is explored. Using a mathematical model of the helium cell discharge and optical pumping process, calculations indicate that substantial gains in sensitivity of a He4 magnetometer are possible. The improvements are obtained by use of larger cells and the replacement of the lamp with a laser as the source of pump radiation. A large cell (2 in. diameter×6 in. long) magnetometer with lamp pumping is calculated to have a sensitivity of 3×10−4 γ/(Hz)1/2, a value which has been experimentally verified. The projected sensitivity of a laser-pumped magnetometer varies between 2×10−5 and 4×10−6 γ/(Hz)1/2, depending on cell size.

An Aeromagnetic Compensation Method Based on a Multimodel for Mitigating Multicollinearity

“…As shown in Figure 3, the scalar magnetometer and the three-axis vector magnetometer were equipped at the pole and the middle of the tail boom, respectively. The scalar magnetometer was a homemade helium magnetometer with sensitivity <0.001nT/√Hz@1Hz; its principle can be seen in [20,21].…”

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

“…where I(z 0 ) is the initial light intensity incident on ∆z, n is the numbers density of the metastable 4 He atoms, Q A is the absorption cross section, Q M is the (dichroic) monitoring cross section, J z is the polarization in the volume element [12,27]. The optical absorption of the polarized 4 He atoms in the cell gradually weakens along the light-propagation direction z.…”

“…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]. However, the central frequency of the laser is easily affected by the environment and can drift away from the resonant frequency of the atomic transition without proper frequency-stabilization mechanism, which induces the light shift.…”

A Magnetic Field Gradiometer based on the Laser Helium Optically Pumped Magnetic Field Sensors

“…Helmholtz coil were used to apply alternating magnetic fields to 4 He atoms. When the frequency of the alternating magnetic fields is equal to the Larmor frequency, NMR occurs and the depolarization process is induced [15][16][17]. In the process of depolarization, transition between adjacent energy levels causes the magnetic moment of atoms to lose its orientation, as shown in Fig.…”