Single-frequency 389-nm CW coherent light source for optical pumping of metastable3He atoms

Abstract

A hyperpolarized helium-3 (³He) has been researched extensively for application in fields such as polarization analysis, ³He spin filtration for n (p, d) γ, and medical imaging. In the medical field, nuclear magnetic resonant imaging (MRI) using hyperpolarized gas is attracted recently because air space in human lungs can be monitored in detail by aspirating polarized gas. There are two methods of producing hyperpolarized ³He gas: spin-exchange optical pumping (SEOP) and metastability exchange optical pumping (MEOP). It is well known that the way of making polarization by the MEOP method is more shortly and more directly. In this study, however, the metastable ³He atoms provided by hollow cathode discharge are polarized by circularly polarized light. When ³He atoms pumped optically, the 2³S-2³P transition at the wavelength of 1083nm is leveraged typically. The ³He atom actually has the optical transition 2³S→ 2³P at 389nm, but the transition has never been used. Therefore, we developed the 389-nm coherent light source to polarize ³He gas by MEOP method. This light source utilized the second harmonic generation (SHG) of continuous-wave Ti:sapphire laser operating at a wavelength of 778nm based on BiB₃O₆ (BiBO) in an external cavity.