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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Application of precision engineering in laser transverse pumping 133Cs brain magnetometers

Takaya Watanabe

Published May 1, 2011• 0 citations
Publisher

Abstract

The transverse relaxation time of the laser pumping of133Cs atomic vaporing. Even if the temperature rises, the extension of the energy distribution of the electron is suppressed the effect of a thermal extension by the quantization and can lower the oscillation threshold to the quantum-dot structure of the VCSEL without causing the decrease in the gain to the utmost limit. The design of the system that measures the brain magnetism at 100fT level. The cause brain magnetic field from 10−13T to 10−14T or more can be detected.

DOI
10.1109/fcs.2011.5977270

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The transverse relaxation time of the laser pumping of133Cs atomic vaporing. Even if the temperature rises, the extension of the energy distribution of the electron is suppressed the effect of a thermal extension by the quantization and can lower the oscillation threshold to the quantum-dot structure of the VCSEL without causing the decrease in the gain to the utmost limit. The design of the system that measures the brain magnetism at 100fT level. The cause brain magnetic field from 10−13T to 10−14T or more can be detected.
The spin-exchange-pumped nuclear magnetic resonance gyroscope (NMRG) is a pivotal tool in quantum navigation. The transverse relaxation of atoms critically impacts the NMRG’s performance parameters and is essential for judging normal operation. Conventional methods for measuring transverse relaxation typically use dual beams, which involves complex optical path and frequency stabilization systems, thereby complicating miniaturization and integration. This paper proposes a method to construct a 133Cs parametric resonance magnetometer using a single-beam vertical-cavity surface-emitting laser (VCSEL) to measure the transverse relaxation of 129Xe and 131Xe. Based on this method, the volume of the gyroscope probe is significantly reduced to 50 cm3. Experimental results demonstrate that the constructed Cs-Xe NMRG can achieve a transverse relaxation time (T2) of 8.1 s under static conditions. Within the cell temperature range of 70 °C to 110 °C, T2 decreases with increasing temperature, while the signal amplitude inversely increases. The research lays the foundation for continuous measurement operations of miniaturized NMRGs.
In the atomic cell of the spin exchange optical pumping system, the optical pumping inevitably introduces a magnetic field gradient, which affects the measurement result of the nuclear spin relaxation time a lot. To address this issue, our method achieves the measurement while excluding the influence of this magnetic field gradient. In this method, the pump laser is turned off after the spins of 87Rb and 129Xe have been effectively polarized, which results in the spin polarization of the 87Rb atoms being provided only by the spin exchange with 129Xe. Ultimately, the transverse and longitudinal components of the polarization of 129Xe are detected by the in situ87Rb atom magnetometer to obtain the T1 and T2 of 129Xe under different conditions. Using our method, since the influence of inhomogeneity caused by the pump laser is eliminated, the relaxation characteristic of atomic cells can be measured more quickly, essentially, and conveniently, which helps compare the performance of different atomic cells and find the best cell fabrication process further.
The magnetic field gradient within optical pumping magnetometers (OPMs) suppresses sensitivity improvement. We investigated the effects of the magnetic field gradient along the x-, y-, and z-axes on the limiting factors of magnetometers under extremely low magnetic field conditions. We modified the magnetic field gradient relaxation model such that it can be applied to atoms in the spin exchange relaxation free (SERF) regime. The gradient relaxation time and spin polarizations, combined with fast spin-exchange interaction, were determined simultaneously using the oscillating cosine magnetic field excitation and amplitude spectrum analysis method. During the experiments, we eliminated the errors caused by the temperature and pumping power, and considered different isotope spin exchange collisions in naturally abundant Rb during the data analysis to improve the fitting accuracy. The experimental results agreed well with those of theoretical calculations and confirmed the accuracy of the improved model. The contribution of the transverse magnetic field gradient to the relaxation of the magnetic field gradient cannot be ignored in the case of small static magnetic fields. Our study provides a theoretical and experimental basis for eliminating magnetic gradient relaxation in atomic sensors in the SERF region.
A high-sensitivity optically pumped atomic magnetometer working in the geomagnetic range utilizing the light-narrowing effect and in-phase excitation is described. The setup is based on a simple pump–probe arrangement built around a Cs vapor cell whose active volume is 64 mm3. The transverse oscillating field is applied parallel to the probe beam to drive Zeeman resonance, and the in-phase component of the resonance signal is measured to determine the field. The sensitivity of the magnetometer is improved by pumping most atoms into the stretched state. Consequently, spin-exchange relaxation is suppressed, and a sensitivity of 0.1 pT/Hz1/2 in the range of 10 μT is achieved. This magnetometer has the advantages of large dynamic range, high performance of low-frequency stabilization, high response speed, and compact size. It can be used for many cutting-edge applications such as detection of magnetic anomalies.
Laser pumping magnetometers using alkali vapors as sensing medium can reach very high sensitivities in magnetic fields covering the range from the earth magnetic field to biological magnetic fields. In this paper, the theoretical analysis and system design of laser pumping cesium magnetometer, cesium atomic energy level formed hyperfine structure with the I-J coupling are discussed. The hyperfine structure is further split into Zeeman sublevels for the effects of magnetic field. The electrons transition is made by using laser pumping and RF magnetic field in the hyperfine structure. The results of magne-to-optical double resonance is obtained. The accurate value of the external magnetic field could be measured by the resonant frequency.
Emerging quantum sensing devices namely atomic magnetometers have become promising candidate for future biomagnetism imaging. However, the limitation of detection bandwidth exists a major drawback for devices of this kind. Conventional approaches, including transverse magnetic field modulation and close-loop control, have seen challenging tradeoffs between size, resolution and bandwidths. In this study, a wide bandwidth zero-field magnetometer with a miniaturized light source has been developed for alternating current (AC) magnetic field detection. A dual-beam Spin-Exchange Relaxation-Free (SERF) magnetometer employing a 4×4×4mm3 alkali metal vapor cell achieves a bandwidth of 188 Hz. This represents a threefold increase in bandwidth compared to non-modulated mode. The sensitivity under modulated mode demonstrated a sensitivity of 55fT/Hz1/2within the frequency range of 10-188Hz. Our results also demonstrated that the sensitivity is constrained by relaxation induced by the modulation of pumping source, so possible tradeoffs can be made based on various applications. The proposed method provides novel approach for bandwidth extension of atomic magnetometers which further pave the way for future applications including magnetoencephalography (MEG), particularly in reducing magnetic noise crosstalk and enhancing spatial resolution.