A polarized 3He system based on metastability-exchange optical pumping

Hyperpolarized ³He nuclei have emerged as a significantly important approach in quantum precision measurement techniques, with extensive applications in fundamental physics, magnetometry, metrology, and beyond. In this study, we report on the design and implementation of a ³He polarization system at the China Mianyang Research Reactor (CMRR), utilizing the metastability-exchange optical pumping (MEOP) method. We employed a Merritt coil system consisting of four square coils to furnish a uniform holding field. We deployed a 2 W fiber laser to pump the metastable ³He atoms and conducted free induction decay (FID) detection of the polarized ³He nuclei using both pickup coil and optical methods. For the optical method, we used a 50 mW linearly polarized distributed Bragg reflector (DBR) laser as the probe. We applied transverse light absorption polarimetry to measure the absolute nuclear polarization of the ground-state ³He. We have developed cell fabrication capabilities at the CMRR, and cells at various pressures ranging from 100 to 1000 Pa have been fabricated and evaluated. For a typical borosilicate cell with 100 Pa pressure, the absolute polarization is measured as P_n ≈ 70%, and the transverse relaxation time is estimated as T₂ ≈ 0.5 s. Moreover, we constructed a few aluminosilicate cells, each carefully filled with pure ³He at a pressure of 100 Pa. Subsequently, we conducted a comprehensive evaluation of their performance in the context of MEOP.