Accurate determination of alkali atom density based on zero-field magnetic resonance in a single-beam spin-exchange relaxation-free atomic magnetometer

Abstract

A single-beam spin-exchange relaxation-free (SERF) atomic magnetometer can extract vector magnetic field information by detecting the transmission intensity of a resonant circularly polarized pumping beam, which depends sensitively on the atomic density of the alkali metal. We present a novel scheme to determine atomic density based on zero-field magnetic resonance. The resonance linewidth under different transverse DC magnetic fields is fitted by means of a quadratic function. The atomic density can be extracted from the quadratic coefficients of the fitted function. The experimental results indicate that the deviation of measured density is less than two times compared with the theoretical values between 378 K and 403 K. Furthermore, the influence of modulation field on resonance linewidth is investigated experimentally and theoretically. A miniature single-beam SERF atomic magnetometer with a sensor head volume of only 16.2 cm3 and the measuring sensitivity of 40 fT/ Hz1/2 has been achieved. These results should be beneficial for guiding the development of a chip-scale atomic magnetometer with high sensitivity and spatial resolution for bio-magnetic field imaging applications.

High-precision alkali-atom density measurement and control methods using light absorption for dual-beam SERF magnetometers

“…For the former method, an empirical formula is popularly used to deduce the saturated alkali vapor from the surface temperature of the vapor cell, which is usually detected by resistive temperature sensors (e.g., platinum resistance) [10,11] . The measurement result obtained by this method can exhibit a deviation from the actual alkali-atom density in the vapor cell [12] . In addition, since the resistive sensor requires driving currents, temperature sensors can inevitably introduce magnetic field interference, which affects the performance of atomic magnetometers [13] .…”

“…Ito et al measured the densities of K and Rb in a co-magnetometer, but this method exhibited an obvious deviation from the theoretical calculation results [16] . Ma et al proposed a precise method for determining alkali-metal density using the atomic spin-exchange relaxation rate in atomic magnetometers [12] . However, the measurement of the spinexchange relaxation rate was time-consuming, which made this method unsuitable for alkali-metal density control.…”

In-situ measurement and close-loop control of atomic number density in an optically pumped magnetometer based on light absorption

“…Taking the single-beam SERF magnetometer as an example, high-precision measurement under the SERF regime requires high atomic number density, and the response signal strength is determined by the transmitted light intensity which is a function of the number density of the alkali metal atoms [16][17][18]. As the density of alkali-metal atoms is determined by the temperature of the vapor cell, accurate measurement of temperature is required for the highprecision atomic magnetometer [19,20]. The temperature of the vapor cell is generally monitored by a resistive temperature sensor (e.g.…”