Application of LNA lasers to helium optical pumping.

摘要

Electron spin-polarized helium 2{dollar}sp3{dollar}S{dollar}sb1{dollar} metastable atoms are a valuable probe of spin-dependent phenomena. Helium metastable atoms can be polarized by illumination with circularly-polarized 1.083 {dollar}mu{dollar}m 2{dollar}sp3{dollar}S{dollar}sb1 leftrightarrow{dollar} 2{dollar}sp3{dollar}P{dollar}sb{lcub}0,1,2{rcub}{dollar} resonance radiation in a process known as optical pumping. Metastable atom polarizations obtained in this manner have been limited by the low intensity of optical pumping radiation available from helium discharge lamps, until now the only practical source of 1.083 {dollar}mu{dollar}m light. However, recent advances in the field of solid-state near-infrared tuneable lasers have resulted in the development of several materials that exhibit laser action at 1.083 {dollar}mu{dollar}m. The most promising of these is a neodymium-doped lanthanum magnesium hexaluminate, known as LNA. During the course of this work several LNA lasers have been designed and fabricated for specialized applications in helium optical pumping. Unstabilized single- and multi-mode lasers have been used to optically pump helium metastable atoms in a flowing helium afterglow, which serves as the basis for a highly competitive polarized electron source that provides electron polarizations approaching 90%. A frequency-stabilized single-mode LNA laser has been developed to optically pump a beam of metastable helium atoms for use in surface studies, and metastable polarizations resulting from its use exceed 96%. Although not designed specifically for other applications, the stabilized laser is ideally suited for application in laser cooling of helium metastable atoms and for helium spectroscopic applications. For example, laser absorption spectroscopy has been used to observe the decay of helium 2{dollar}sp3{dollar}S{dollar}sb1{dollar} atoms as they are converted into He{dollar}sb2{dollar}(a {dollar}sp3Sigmasbsp{lcub}rm u{rcub}{lcub}+{rcub}{dollar}) molecules in three-body reactions in a high-pressure helium afterglow, revealing interesting phenomena possibly related to quantum mechanical tunneling. The present work shows that LNA lasers have an important future in helium optical pumping.