Modulation of laser's left-handed and right-handed polarization was used in the paper. This method has realized all-optical detection of magnetic field and avoided cross talk existing in conventional atomic magnetometer. The detection principle of precession frequency of atomic magnetic moment in magnetic field was demonstrated based on the method, and the signal was analyzed, then the detection and processing system was designed based on the analysis. The in-phase signal was displayed as Lorenz lineshape. The quadrature signal was displayed as dispersion lineshape, and the magnitude was 0 at resonance frequency. The phase signal was displayed as monotonically decreasing function with frequency, and the magnitude was 0 at resonance frequency. Both the quadrature and phase signals can be used to lock resonance frequency and realize measurement of magnetic field.
Modulation of laser's left-handed and right-handed polarization was used in the paper. This method has realized all-optical detection of magnetic field and avoided cross talk existing in conventional atomic magnetometer. The detection principle of precession frequency of atomic magnetic moment in magnetic field was demonstrated based on the method, and the signal was analyzed, then the detection and processing system was designed based on the analysis. The in-phase signal was displayed as Lorenz lineshape. The quadrature signal was displayed as dispersion lineshape, and the magnitude was 0 at resonance frequency. The phase signal was displayed as monotonically decreasing function with frequency, and the magnitude was 0 at resonance frequency. Both the quadrature and phase signals can be used to lock resonance frequency and realize measurement of magnetic field.
Atomic magnetometers use the coherent precession of polarized atomic spins to detect and measure magnetic fields. When an off-resonant, linearly polarized probe beam propagates through the atomic vapor cell, the precession will cause a rotation of its polarization plane. Measuring the angle of the rotation, the magnetic field can be calculated. In this paper, we introduce the basic principles of atomic magnetometers and describe the method to measure the angle. Then a dual-phase lock-in amplifier (LIA) is proposed to detect the weak signal of the atomic magnetometer. And we design a simulation for the LIA based on Matlab/Simulink. Our theoretical analysis and simulation results show that the detecting system is well working and it is possible to detect weak signal of magnetic fields in an accurate way.
In order to availably solve the crosstalk of the traditionally optically pumped magnetometer,in which an oscillating magnetic field drives transitions between Zeeman magnetic sublevels,an all-optical cesium(Cs)atomic magnetometer based on Bell-Bloom structure has been investigated and demonstrated experimentally in this paper.When there is an external magnetic field,by analyzing the Larmor precession spectrum of the polarized ground state atoms induced by a modulated pump laser,the atomic magnetometer with high sensitivity is achieved.First,we present the operating principle of the magnetometer with amplitude modulation and set up the experimental system by means of a three-layer magnetic shield.Then in the case of 100 nT field by optimizing the experimental parameters,i.e.,the frequency and intensity of the pump laser,we have obtained the atomic precession spectrum with line width(full width at half maximum)of 22 Hz and signal noise ratio(SNR)of 3.2×104 per unit hertz band width,and then have evaluated the magnetometer with an intrinsic sensitivity of 100fT/Hz1/2 and spatial resolution smaller than 1.2cm,while the experimentally closed loop test shows that the cesium atomic magnetometer would have the sensitivity of 120fT/Hz1/2 and response time of 300 ms.
We report a rubidium atomic magnetometer based on pump-probe nonlinear magneto-optical rotation. The rubidium vapor cell is placed in a five-layer magnetic shield with inner coils that can generate uniform magnetic fields along the direction of pump beam, and the cell is also placed in the center of a Helmholtz coil that can generate an oscillating magnetic field perpendicular to the direction of pump beam. The atoms are optically pumped by circularly polarized pump beam along a constant magnetic field in a period of time, then the pump beam is turned off and a /2 pulse of oscillating magnetic field for 87Rb atoms is applied. After the above process, the individual atomic magnetic moments become phase coherent, resulting in a transverse magnetization vector precessing at the Larmor frequency in the magnetic field. The linearly polarized probing beam is perpendicular to the direction of magnetic field, and can be seen as a superposition of the left and right circularly polarized light. Because of the different absorptions and dispersions of the left and right circularly polarized light by rubidium atoms, the polarization direction of probing beam rotates when probing beam passes through rubidium vapor cell. The rotation of the polarization is subsequently converted into an electric signal through a polarizing beam splitter. Finally, the decay signal related to the transverse magnetization vector is measured. The Larmor frequency proportional to magnetic field is obtained by the Fourier transform of the decay signal. The value of magnetic field is calculated from the formula:B=(2/) f, where and f are the gyromagnetic ratio and Larmor frequency, respectively. In order to measure the magnetic field in a wide range, the tracking lock mode is proposed and tested. The atomic magnetometer can track the magnetic field jump of 1000 nT or 10000 nT, indicating that the atomic magnetometer has strong locking ability and can be easily locked after start-up. The main performances in different magnetic fields are tested. The results show that the measurement range of the atomic magnetometer is from 100 nT to 100000 nT, the extreme sensitivity is 0.2 pT/Hz1/2, and the magnetic field resolution is 0.1 pT. The transverse relaxation times of the transverse magnetization vector in different magnetic fields are obtained, and the relaxation time decreases with the increase of the magnetic field. When the measurement range is from 5000 nT to 100000 nT, the magnetic field sampling rate of the atomic magnetometer can be adjusted in a range from 1 Hz to 1000 Hz. The atomic magnetometer in high sampling rate can measure weak alternating magnetic field at low frequency. This paper provides an important reference for developing the atomic magnetometer with large measurement range, high sensitivity and high sampling rate.
Based on power modulation of a pump laser and precessional projection detection, we present an all-optical vector magnetometer of cesium, which has a demonstrated magnitude sensitivity of 80 fT/Hz 1/2 and an orientation sensitivity of 0.1°/Hz 1/2 . In the device, four main factors are measured experimentally, which are the Larmor precession frequency of a polarized magnetic moment that depends on the modulus of the measured magnetic field only, two phase shifts and amplitude ratio of the precession projection in the two probe directions relative to the magnetic field orientation. This kind of magnetometer with high sensitivity in the range of the spatial angle is suitable for solving the inverse problem and geomagnetic navigation.
A new method for the detection of atomic spin precession based on the Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. Different from the conventional polarization detection methods which obtain the atomic spin precession signal by measuring the change of the probe laser power, the proposed method uses the laser modulated by an electro-optic phase modulator (EOM) as the source of the interferometer, and obtains the atomic spin precession signal by measuring the phase difference between the two arms of the MZI. The output of interferometer is independent of the probe laser power, which avoids the system error caused by the fluctuation of the probe laser power, and the long-term stability of the system is effectively improved. At the same time, the method adopts high-frequency electro-optic modulation, which can effectively suppress low-frequency noise, such as 1/f noise, and can significantly improve the detection sensitivity. The rotation sensitivity and long-term stability of the atomic comagnetometer were tested using the MZI detection method and a typical detection method, respectively. The comparison results show that the proposed method has the highest low frequency sensitivity and the potential to improve the long-term stability of the system.
Abstract We present an ultrahigh-sensitivity electro-optic modulator (EOM) detection method for detecting the atomic Larmor precession in an all-optical K–Rb hybrid atomic magnetometer operating in the spin-exchange relaxation-free regime. A magnetic field sensitivity of ~10 f T Hz −1/2 has been achieved by optimizing the probe laser parameters and the EOM modulation conditions, which is comparable to that with the Faraday modulation method and has a better performance than the balanced polarimetry method in the low frequency range. The EOM detection method in the atomic magnetometer presents several advantages, such as simple structure, no extra magnetic noise, moderate thermal effect, high measurement sensitivity and reliable stability. It is demonstrated to be feasible for the improved compactness and simplicity of atomic magnetic field measurement devices in the future.