An all-optical scalar and vector spin-exchange relaxation-free magnetometer employing on–off pump modulation

Abstract

It is demonstrated that a spin-exchange relaxation-free (SERF) atomic magnetometer can be used for scalar measurements with no additional hardware. Because of relaxation processes, an ensemble of alkali atoms needs a constant supply of polarized photons by a pump beam to maintain a polarized state. If the pump beam is shuttered off, the system decays to its equilibrium state. For a low enough relaxation rate and with a magnetic field present, the system will exhibit oscillations at its natural frequencies. In a SERF magnetometer, it happens at the Zeeman resonance frequency of the atoms (Larmor frequency). Thus, shuttering off the pump beam reveals oscillations at the Larmor frequency. From this frequency, one can deduce the scalar value of the applied magnetic field. As a result, all-optical scalar measurements can be performed. At the same time, either one or two vector components of the applied field can be measured by using one or two orthogonal probe beams, respectively. In a low-polarization SERF regime, the ground state can be well described by the Bloch equations for the electron spin polarization. By solving the time-dependent Bloch equations [neglecting the diffusion term and assuming that the nuclear slowing-down factor q(P) is constant], the oscillation frequency of the system is obtained. From this frequency, the scalar value of the applied magnetic field is derived. It is shown that applied fields down to 1 nT can be measured with a 0.1% relative uncertainty. Fields down to 50 pT can be measured with a 10% relative uncertainty. The time dependence acquired in the "off" periods is strongly correlated with the Zeeman sublevels population of the atomic ground state and reveals its spin dynamics.

Measurement of129Xe frequency shift due to Cs—129Xe collisions

“…1 and is described elsewhere. [18][19][20] Two cubic glass cells with a side of 2 cm were each filled with a droplet of Cs metal, 20 torr of 129 Xe, 700 torr of N 2 , and 50 torr (1 torr = 1.33322×10 2 Pa) of 129 Xe, 700 torr of N 2 . The cells were placed in a nonmagnetic oven and heated to 80 • C-90 • C by the flowing hot air.…”

“…In the measurements described below, all three components of the magnetic field had been compensated to be close to zero to keep the system in the Spin-Exchange Relaxation-Free (SERF) regime. [18][19][20] Cs atoms were circularly polarized by the pump beam through a polarizer and a 1/4 wave plate along the z direction. 129 Xe atoms were polarized by spinexchange collisions with polarized Cs atoms.…”

Spin-exchange relaxation-free magnetic gradiometer with dual-beam and closed-loop Faraday modulation

“…To obtain a high sensitivity at the low frequency, the optical rotation angle is usually modulated so that the signal is separated from 1∕f noise. The common modulation technique is Faraday modulation polarimetry [5][6][7]13], which has the benefit that the rotation signal is isolated from low-frequency noise compared with balanced polarimetry. However, Faraday modulation polarimetry suffers from laser intensity noise, thermal noise generated by the Faraday modulator, and nonmagnetic technical noise.…”

Optimized Design of a Pump Laser System for a Spin Exchange Relaxation Free Inertial Measurement Device

“…In terms of the study of the pump method and power stability for the pump laser, compared with the pump method of non-modulation [ 12 , 13 ] and sinusoidal modulation [ 14 , 15 ], the pump method of square wave modulation [ 16 , 17 , 18 ] is more suitable for mobile platforms with the characteristics of less influence from the external environment, high data repeatability and high response frequency. The power stabilization method of the pump laser includes the electric control method [ 19 ], the electro-optic modulator method [ 20 ], liquid crystal variable retarder method [ 21 ], etc., while the acousto-optic modulator method not only gives a high extinction ratio, but can also modulate the first-order diffraction light with the opening and closing signal [ 16 ].…”