All-optical Atomic Magnetometer Research Articles

Ultra-sensitive measurement of small optical rotation angles using quantum entanglement based on a quasi-Wollaston prism beam splitter

The measurement of optical rotation is fundamental to optical atomic magnetometry. Ultra-high sensitivity has been achieved by employing a quasi-Wollaston prism as the beam splitter within a quantum entanglement state, complemented by synchronous detection. Initially, we designed a quasi-Wollaston prism and intentionally rotated the crystal axis of the exit prism element by a specific bias angle. A linearly polarized light beam, incident upon this prism, is divided into three beams, with the intensity of each beam correlated through quantum entanglement. Subsequently, we formulated the equations for optical rotation angles by synchronously detecting the intensities of these beams, distinguishing between differential and reference signals. Theoretical analysis indicates that the measurement uncertainty for optical rotation angles, when using quantum entanglement, exceeds the conventional photon shot noise limit. Moreover, we have experimentally validated the effectiveness of our method. In DC mode, the experimental results reveal that the measurement uncertainty for optical rotation angles is 4.7 × 10−9 rad, implying a sensitivity of 4.7 × 10−10 rad/Hz1/2 for each 0.01 s measurement duration. In light intensity modulation mode, the uncertainty is 48.9 × 10−9 rad, indicating a sensitivity of 4.89 × 10−9 rad/Hz1/2 per 0.01 s measurement duration. This study presents a novel approach for measuring small optical rotation angles with unprecedentedly low uncertainty and high sensitivity, potentially playing a pivotal role in advancing all-optical atomic magnetometers and magneto-optical effect research.

Vector measurements using all optical scalar atomic magnetometers

Vector field measurement is demonstrated with an all-optical scalar atomic magnetometer using intrinsic parameters related to its scalar operation. The Bell-Bloom type atomic magnetometer measures the Larmor precession of cesium atoms through on-resonant absorption of a probe beam. While the AC component of the probe signal is used for the field magnitude measurement, the probe DC signal contains information about the polar angle, defined as the angle between the magnetic field and the probe beam. Additional polar angle information is obtained from the light-shift-induced magnetic field caused by the frequency modulation of the probe beam. With a measurement time of 100 ms, better than 0.02° sensitivity has been achieved using a commercial miniaturized sensor at the optimal sensor orientation. The angle measurement accuracy is checked against an optical encoder over the entire polar angle range of 0°–180°. Better than 1° error is recorded over most set polar angles. Azimuthal angle measurement is also exhibited with two orthogonally oriented sensors.

Magneto-optical spectroscopy with arbitrarily polarized intensity-modulated light in He4 atoms

We present both a theoretical and experimental study of the magneto-optical spectra induced with intensity-modulated resonant laser light that synchronously pumps and detects the metastable $^{4}\mathrm{He}$ atoms in the presence of a quasistatic magnetic field. We extend previous work and derive complete analytical expressions for the resonance signals by taking into account arbitrary magnetic-field directions and arbitrary light polarizations. The analytical results are derived by solving the Liouville equation using the irreducible tensor formalism on the assumption of low light power. We discuss the potential application of the derived analytical results in constructing and optimizing a dead-zone-free all-optical atomic magnetometer.

Herriott-cavity-assisted all-optical atomic vector magnetometer

We report an all-optical atomic vector magnetometer using dual Bell-Bloom optical pumping beams in a Rb vapor cell. This vector magnetometer consists of two orthogonal optical pumping beams, with amplitude modulations at $^{85}$Rb and $^{87}$Rb Larmor frequencies respectively. We simultaneously detect atomic signals excited by these two pumping beams using a single probe beam in the third direction, and extract the field orientation information using the phase delays between the modulated atomic signals and the driving beams. By adding a Herriott cavity inside the vapor cell, we improve the magnetometer sensitivity. We study the performance of this vector magnetometer in a magnetic field ranging from 100~mG to 500~mG, and demonstrate a field angle sensitivity better than 10~${\mu}$rad/Hz$^{1/2}$ above 10~Hz.

Enhanced fully optically pumped magnetic resonance with optical sideband auxiliary pumping

We have proposed a new technique to obtain highly polarized atoms for improving the sensitivity of the all-optical Cs atomic magnetometer. In a Bell–Bloom magnetometer, the resonance pumping from the ground state F g = 3 to the excited state F e = 4 at the D1 line is used to polarize the Cs atoms and populate the sublevels of the | F g = 4 , m F = 4 ⟩ partly as the transition F g = 4 → F e = 3 remains leaking. Here we utilize a modulation technique to generate a sideband frequency to pump both transitions simultaneously, which drives more atoms to the target state | F g = 4 , m F = 4 ⟩ . This improvement significantly increases the magnetic resonance signal but with little effect on its linewidth. It is very suitable for the miniaturization of the atomic magnetometer in the future.

On-Site Synchronous Determination of Coil Constant and Nonorthogonal Angle Based on Electron Paramagnetic Resonance

An on-site and fast synchronous measurement of coil constant and nonorthogonal angle, using an all-optical atomic magnetometer, was reported in this article. Based on the spectrum analysis of electron paramagnetic resonance of spin-polarized potassium under different magnetic fields, the measurement models of coil constant and nonorthogonal angle were established, according to which we experimentally obtained the weighted average results with related estimated uncertainties: the coil constants in the x-, y-, and z-axes were (145.9 ± 0.3) nT/mA, (149.5 ± 0.3) nT/mA, and (129.6 ± 0.1) nT/mA, respectively; the nonorthogonal angles existing in the xz and yz axes were (0.11 ± 0.02)° and (0.23 ± 0.02)°, respectively. The determination results of the residual magnetic field in the z-axis, with two comparative experiments, demonstrated the validity of this on-site synchronous measurement method. The present method can be easily used in calibrating coil constant and nonorthogonal angle for all-optical atomic magnetometers, especially for miniaturized ones.

Is light narrowing possible with dense-vapor paraffin coated cells for atomic magnetometers?

We investigated the operation of an all-optical rubidium-87 atomic magnetometer with amplitude-modulated light. To study the suppression of spin-exchange relaxation, three schemes of pumping were implemented with room-temperature and heated paraffin coated vacuum cells. Efficient pumping and accumulation of atoms in the F=2 ground state were obtained. However, the sought-for narrowing of the resonance lines has not been achieved. A theoretical analysis of the polarization degree is presented to illustrate the absence of light narrowing due to radiation trapping at high temperature.

On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

Measurement Sensitivity Improvement of All-Optical Atomic Spin Magnetometer by Suppressing Noises.

Quantum manipulation technology and photoelectric detection technology have jointly facilitated the rapid development of ultra-sensitive atomic spin magnetometers. To improve the output signal and sensitivity of the spin-exchange-relaxation-free (SERF) atomic spin magnetometer, the noises influencing on the output signal and the sensitivity were analyzed, and the corresponding noise suppression methods were presented. The magnetic field noises, including the residual magnetic field noise and the light shift noise, were reduced to approximately zero by employing the magnetic field compensation method and by adjusting the frequency of the pump beam, respectively. With respect to the operation temperature, the simulation results showed that the temperature of the potassium atomic spin magnetometer realizing the spin-exchange relaxation-free regime was 180 °C. Moreover, the fluctuation noises of the frequency and the power were suppressed by using the frequency and the power stable systems. The experimental power stability results showed that the light intensity stability was enhanced 10%. Contrast experiments on the sensitivity were carried out to demonstrate the validity of the suppression methods. Finally, a sensitivity of 13 fT/Hz1/2 was successfully achieved by suppressing noises and optimizing parameters.

A dead-zone free ⁴He atomic magnetometer with intensity-modulated linearly polarized light and a liquid crystal polarization rotator.

We demonstrate an all-optical (4)He atomic magnetometer experimental scheme based on an original Bell-Bloom configuration. A single intensity-modulated linearly polarized laser beam is used both for generating spin polarization within a single (4)He vapor and probing the spin precessing under a static magnetic field. The transmitted light signal from the vapor is then phase-sensitively detected at the modulation frequency and its harmonics, which lead to the atomic magnetic resonance signals. Based on this structure, a liquid crystal is added in our magnetometer system and constitutes a polarization rotator. By controlling the voltage applied on the liquid crystal, the light linear polarization vector can be kept perpendicular with the ambient magnetic field direction, which in turn provides the maximum resonance signal amplitude. Moreover, the system exhibits a magnetic-field noise floor of about 2pT/√Hz, which is not degraded due to the presence of the liquid crystal and varying magnetic field direction. The experiment results prove that our method can eliminate the dead-zone effect, improve the system spatial isotropy, and thus be suitable in mobile applications.

A Novel Calibration Method Research of the Scale Factor for the All-optical Atomic Spin Inertial Measurement Device

School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191, China(Received March 23, 2015 : revised June 9, 2015 : accepted July 6, 2015)A novel method to measure the scale factor for the all-optical atomic spin inertial measurement device (ASIMD) is demonstrated in this paper. The method can realize the calibration of the scale factor by a self-consistent method with small errors in the quiescent state. At first, the matured IMU (inertial measurement unit) device was fixed on an optical platform together with the ASIMD, and it has been used to calibrate the scale factor for the ASIMD. The results show that there were some errors causing the inaccuracy of the experiment. By the comparative analysis of theory and experiment, the ASIMD was unable to keep pace with the IMU. Considering the characteristics of the ASIMD, the mismatch between the driven frequency of the optical platform and the bandwidth of the ASIMD was the major reason. An all-optical atomic spin magnetometer was set up at first. The sensitivity of the magnetometer is ultra-high, and it can be used to detect the magnetization of spin-polarized noble gas. The gyromagnetic ratio of the noble gas is a physical constant, and it has already been measured accurately. So a novel calibration method for scale factor based on the gyromagnetic ratio has been presented. The relevant theoretical analysis and experiments have been implemented. The results showed that the scale factor of the device was 7.272 V/°/s by multi-group experiments with the maximum error value 0.49%.Keywords : Scale factor, All-optical, Atomic spin, Inertial measurement deviceOCIS codes : (230.1150) All-optical devices; (230.5160) Photo detectors; (280.4788) Optical sensing and sensors; (020.1335) Atom optics

Research on the influence of alkali polarization on an all-optical atomic spin magnetometer based on hybrid pumping potassium and rubidium

An all-optical atomic spin magnetometer using a hybrid cell of K and Rb atoms is demonstrated in this paper. Via deriving and solving the Bloch equations, we established the models for the polarization rate of Rb and the magnetometer’s output signal, respectively. In order to achieve the maximum sensitivity, we carried out research on the influence of the pump power on the polarization rate and magnetometer’s output signal. The magnetometer’s sensitivity was found to be proportional to the polarization rate of Rb, which was confined by the pump power. In a certain context, theoretical predictions indicated that the larger the pump power was, the higher magnetometer’s sensitivity that could be realized. However, the theoretical estimate deviated from the experimental results. An analysis of the errors between the actual value and the theoretical value showed that the different molar ratio between the two species of alkali-metal atoms was the primary reason causing the deviation. By comparing the experimental measurement result with simulation result, we found the difference in the molar ratio to be approximate 4 times. After various parameters had been optimized, a sensitivity of 18 fT/Hz1/2 was achieved by analyzing the signal-to-noise ratio.

Magnetization produced by spin-polarized xenon-129 gas detected by using all-optical atomic magnetometer

The method to produce spin-polarized xenon-129 gas was based on the method of spin-exchange optical pumping (SEOP). The magnetizations produced by the hyperpolarized (HP) xenon-129 gas were analyzed from the perspective of theoretical and experimental research. The theoretical simulation was based on the conventional Bloch equation. The experimental research was based on measurements made by using an all-optical atomic magnetometer. The experimental results agreed with the theoretical simulated results, which proved that an all-optical atomic magnetometer had the ability to measure the magnetic field produced by xenon-129 nuclei in a low external magnetic field. Because the frequency of the nuclear spin precession could be detected precisely, the results showed that the mean measurement error of the gyromagnetic ratio was 1.1 × 10 -4 Hz/nT.

Noise characterization of an atomic magnetometer at sub-millihertz frequencies

Noise measurements have been carried out in the LISA bandwidth (0.1–100mHz) to characterize an all-optical atomic magnetometer based on nonlinear magneto-optical rotation. This was done in order to assess if the technology can be used for space missions with demanding low-frequency requirements like the LISA concept. Magnetometry for low-frequency applications is usually limited by 1/f noise and thermal drifts, which become the dominant contributions at sub-millihertz frequencies. Magnetic field measurements with atomic magnetometers are not immune to low-frequency fluctuations and significant excess noise may arise due to external elements, such as temperature fluctuations or intrinsic noise in the electronics. In addition, low-frequency drifts in the applied magnetic field have been identified in order to distinguish their noise contribution from that of the sensor. We have found the technology suitable for LISA in terms of sensitivity, although further work must be done to characterize the low-frequency noise in a miniaturized setup suitable for space missions.

Magnetic induction tomography using an all-optical ⁸⁷Rb atomic magnetometer.

We demonstrate magnetic induction tomography (MIT) with an all-optical atomic magnetometer. Our instrument creates a conductivity map of conductive objects. Both the shape and size of the imaged samples compare very well with the actual shape and size. Given the potential of all-optical atomic magnetometers for miniaturization and extreme sensitivity, the proof-of-principle presented in this Letter opens up promising avenues in the development of instrumentation for MIT.

抽运光频率对全光Cs原子磁力仪灵敏度的影响

抽运光频率对全光Cs原子磁力仪灵敏度的影响

Magnetic induction measurements using an all-optical 87Rb atomic magnetometer

In this work we propose, and experimentally demonstrate, the use of a self-oscillating all-optical atomic magnetometer for magnetic induction measurements. Given the potential for miniaturization of atomic magnetometers, and their extreme sensitivity, the present work shows that atomic magnetometers may play a key role in the development of instrumentation for magnetic induction tomography.

The Effects of Pump Beam on Cesium Magnetometer Sensitivity

This paper described an all-optical cesium atomic magnetometer whose measuring sensitivity achieves 0.3pT/Hz1/2. In order to achieve high measuring sensitivity, the dominant parameter, a circularly polarized pumping laser which is used to polarize the cesium atoms was well discussed. After a series of experimental tests, the relationships between the output signals based on absorptive detection with pump beam were expressed here. When the optical pumping frequency was stabilized to the center of the resonance line Fg =3→Fe=4 of the cesium D1 transition, it was found that the optimum pump beam intensity was 6 mW/cm2 for this kind of magnetometer to achieve its highest sensitivity.

All-Optical Cesium Atomic Magnetometer with High Sensitivity

An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported. The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together. The frequency response of the rotational spectrum is 1.8 mrad/Hz at Larmor precession resonance. Analyzing the signal-to-noise ratio from the experimentally observed spectrum, we predict that the magnetic measurement sensitivity of 0.3 pT/Hz1/2 would be obtained in the responsive range from 20 nT to 2000 nT.

All-optical magnetometry for NMR detection in a micro-Tesla field and unshielded environment

An all-optical atomic magnetometer is used to detect a proton free-precession signal from a water sample polarized in a 0.7 T field and remotely analyzed in a 4 μT field. Nuclear spins are manipulated either by π / 2 pulses or by non-adiabatic rotation. The magnetometer operates at room temperature, in an unshielded environment and has a dual-channel sensor for differential measurements.