Nuclear magnetic resonance gyroscopes (NMRGs) have broad application perspectives with the advantages of low cost, low power consumption, miniaturization-ability and high precision. The transverse relaxation rate of noble gas nuclear spins is used to evaluate the performance of vapor cell, which also affects the angle random walk (ARW) of NMRG systems. The inhomogeneity of electronic spin polarization spatial distribution is one of the essential sources of the transverse relaxation rate. In this paper, we study the influence of the pump power and beam diameter in the transverse relaxation rate of noble gas nuclear spins through numerical simulations of electronic spin polarization and experimental measurements of transverse relaxation time. Simulations of the electronic spin polarization spatial distribution are proposed based on the Bloch–Torrey equations. The transverse relaxation time of noble gas nuclear spins under different pump power and beam diameters is measured by the free induction decay (FID) method. Experimental results show that the transverse relaxation rate of nuclear spins increases with pump power. The relaxation rate with a 2.3mm pump beam diameter is larger than with a 1.3mm diameter. Furthermore, we innovatively find that the transverse relaxation rate shows a linear relationship with the electronic spin polarization obtained from the numerical simulation. This work provides a reference for the study of nuclear spin relaxation and the optimization of the parameters of the pump beam in NMRGs.
The integrated Vertical-Cavity Surface-Emitting Lasers (VCSELs) modules have been widely researched and manufactured accompanying with the rapid development of compact atomic magnetometers, atomic gyroscopes, atomic clocks, and the other atomic sensors. For atomic magnetometers operating in the Spin-Exchange Relaxation-Free (SERF) regime, the vapor cell should be heated to a high temperature, which may cause the built-in laser chip over-heated and module structural or optical component deformation, lowering the performance of the built-in laser module. Meanwhile, due to the space constraints, the laser module needs to achieve a large collimation beam diameter and the non-magnetic structure should be optimized to have high temperature tolerance and stable thermal dissipation. In this study, a compact non-magnetic VCSEL module is developed based on the non-magnetic structure with the abilities of optical path alignment, beam collimation, and polarization conversion. Compared with the common TO-can packaging, the proposed VCSEL module achieved low residual magnetic field generated. And the entire volume is less than 1 cm3 with the collimating beam diameter of 2 mm. The experiment evaluation result shows that the laser module could work stably in high temperature with stable thermal dissipation and sufficient thermal margin (60±10℃) for precise wavelength tuning and maintain optical performance and structural for meeting the demand of pump laser in the SERF atomic magnetometers.
Nuclear magnetic resonance gyroscopes(NMRG) have received widespread attention to the fields of national defense and civil applications due to their potential for miniaturization and low cost. The relaxation time is an important parameter to measure the performance of the alkali vapor cell of the NMR gyroscope, the most commonly used industry standard measurement method of longitudinal relaxation time(T1) is the measurement method using π pulse plus 1/2π pulse, so the measurement accuracy of the T1 is affected by the accuracy of the pulse duration. Usually the maximum value of the signal amplitude correspond to the time of 1 /2πpulse duration, but it cannot eliminate the influence of the random error of the system, the use of multiple cycles to automatically fit the pulse duration improves the accuracy of the pulse duration, saves a lot of measurement time, eliminates human error, and ultimately improves the T1 measurement accuracy.
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