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Register a new userIntegrated optically pumped magnetometer for measurements within Earths magnetic field
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We present a portable optically pumped magnetometer instrument for ultra-sensitive measurements within the Earths magnetic field. The central part of the system is a sensor head operating a MEMS-based Cs vapor cell in the light-shift dispersed Mz mode. It is connected to a compact, battery-driven electronics module by a flexible cable. We briefly review the working principles of the device and detail on the realization of both, sensor head and electronics. We show shielded and unshielded measurements within a static magnetic field amplitude of 50 uT demonstrating a noise level of the sensor system down to 100 fT/sqrt{Hz} and a sensor bandwidth of several 100 Hz. In a detailed analysis of sensor noise we reveal the system to be limited by technical sources with straightforward strategies for further improvement towards its fundamental noise limit of 12 fT/sqrt{Hz}. We compare our sensors performance to a commercial SQUID system in a measurement environment typical for geomagnetic observatory practice and geomagnetic prospection.
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We experimentally investigate the influence of the orientation of optically pumped magnetometers in Earths magnetic field. We focus our analysis to an operational mode that promises femtotesla field resolu-tions at such field strengths. For this so-called light-shift dispersed Mz(LSD-Mz) regime, we focus on the key parameters defining its performance. That are the reconstructed Larmor frequency, the transfer function between output signal and magnetic field amplitude as well as the shot noise limited field resolution. We demonstrate that due to the use of two well balanced laser beams for optical pumping with different helicities the heading error as well as the field sensitivity of a detector both are only weakly influenced by the heading in a large orientation angle range.
When optically pumped magnetometers are aimed for the use in Earths magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement result. Measurement errors and inaccuracies related to the heading of the sensor can be an even more severe problem in the case of special operational configurations, such as for example the use of strong off-resonant pumping. We systematically study the main contributions to the heading error in systems that promise high magnetic field resolutions at Earths magnetic field strengths, namely the non-linear Zeeman splitting and the orientation dependent light shift. The good correspondence of our theoretical analysis to experimental data demonstrates that both of these effects are related to a heading dependent modification of the interaction between the laser light and the dipole moment of the atoms. Also, our results promise a compensation of both effects using a combination of clockwise and counter clockwise circular polarization.
We present first, encouraging results obtained with an experimental apparatus based on Coherent Population Trapping and aimed at detecting biological (cardiac) magnetic field in magnetically compensated, but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection for cancellation of (common mode) magnetic noise. Synchronous data acquisition with a reference (electro-cardiographic or pulse-oximetric) signal allows for improving the S/N in an off-line averaging. The set-up has the relevant advantages of working at room temperature with a small-size head, and of allowing for fast adjustments of the dc bias magnetic field, which results in making the sensor suitable for detecting the bio-magnetic signal at any orientation with respect to the heart axis and in any position around the patient chest, which is not the case with other kinds of magnetometers.
We report on a two-channel magnetometer based on nonlinear magneto-optical rotation in a Cs glass cell with buffer gas. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D$_2$ line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment and spurious signal from distant magnetic sources is rejected by means of differential measurement. In this regime the magnetometer simultaneously gives the magnetic field modulus and the field difference. Rejection of the common-mode noise allows for high-resolution magnetometry with a sensitivity of pthz{2}. This sensitivity, in conjunction with long-term stability and a large bandwidth, makes possible to detect water proton magnetization and its free induction decay in a measurement volume of 5 cm$^3$
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.
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