An Optically Pumped Magnetometer Working in the Light-Shift Dispersed Mz Mode

Abstract

We present an optically pumped magnetometer working in a new operational mode—the light-shift dispersed Mz (LSD-Mz) mode. It is realized combining various features; (1) high power off-resonant optical pumping; (2) Mz configuration, where pumping light and magnetic field of interest are oriented parallel to each other; (3) use of small alkali metal vapor cells of identical properties in integrated array structures, where two such cells are pumped by circularly polarized light of opposite helicity; and (4) subtraction of the Mz signals of these two cells. The LSD-Mz magnetometer’s performance depends on the inherent and very complex interplay of input parameters. In order to find the configuration of optimal magnetometer resolution, a sensitivity analysis of the input parameters by means of Latin Hypercube Sampling was carried out. The resulting datasets of the multi-dimensional parameter space exploration were assessed by a subsequent physically reasonable interpretation. Finally, the best shot-noise limited magnetic field resolution was determined within that parameter space. As the result, using two 50 mm3 integrated vapor cells a magnetic field resolution below 10 fT/√Hz at Earth’s magnetic field strength is possible.

Performance analysis of an optically pumped magnetometer in Earth’s magnetic field

“…Since this value is in agreement with the fitting parameter, we identify the strong power of the detuned laser as one important source of broadening of the magnetic resonance. This is already close to the optimal conditions [21]. This optimal resolution is found in the case of parallel alignment of the laser direction to the magnetic field.…”

“…In this context, the newly introduced operational modes which enable shot-noise-limited field resolutions of OPMs on the femtotesla scale in Earth's magnetic field strengths are promising alternatives. Namely, those are the light narrowing (LN) [18][19][20] and the LSD-Mz [21] mode.…”

Reduction of frequency-dependent light shifts in light-narrowing regimes: A study using effective master equations

“…This is equivalent to a left-handed circularly polarized pump laser propagating antiparallel to the direction of the magnetic field. In this case, we only need to change B 0 to −B 0 in the effective master equation (18), while keeping the definition of the z-direction that defines the magnetic states. With the Rabi frequency Ω = 4.1 MHz, spin exchange rate γ se = 1.31 KHz, total spin relaxation rate γ = 1.53 KHz, and excited states' energy broadening Γ = 0.6 GHz for the 100 torr nitrogen case, while γ = 1.65vKHz, Γ = 4.2 GHz for the 700 torr nitrogen case, we numerically solve the master equation (18) for ρ g in the long term limit.…”

“…To have a collective spin precession for measurement, the electronic spins are polarized by optical pumping [10][11][12][13]. However, in the measurement of the Larmor frequency, the light shift, resulting from the interaction of light (the pump beam here) and matter, behaves as an effective magnetic field to the atomic spins, and subsequently shifts its precession frequency [14][15][16][17][18]. This light shift is dependent on the intensity and frequency of the pump laser.…”

Pulsed operation of a miniature scalar optically pumped magnetometer

“…Microfabricated scalar sensors have reached sensitivities of 5 pT/Hz 1/2 in a volume of 2 mm 3 with a bandwidth of 1 kHz [31]. Using the effect of light narrowing, sensitivities of 42 fT/Hz 1/2 in an active volume of 9.3 mm 3 and 10 fT/Hz 1/2 in 50 mm 3 were predicted, if the noise were photon shot noise-limited [28,29]. In an actual measurement, a good sensitivity of 320 fT/Hz 1/2 was reached in a relatively small cell of 50 mm 3 [32].…”