A scheme for production of polarized beams of metastable 3He has been described. This scheme takes into account the recent advances in laser technology to optically pump 3He in the metastable 3S1 state and subsequent collisional transfer to ground state atoms. (AIP)
A practical light source for optical pumping necessarily excites transitions other than those which it is desired should be excited. It is shown that a pumping light source for 23S13He may be characterized by three parameters, which describe the transition rates for Δm = ±1, and 0, transitions under standard conditions. Expressions are derived relating these parameters to the geometry of the light source. The equation which describes the flow of angular momentum into 3He is formulated, using these parameters, the light flux, the lifetime of the metastable atoms, and collisional mixing in the 23P states. This equation is solved to give the polarization which may be attained, and the rate at which the polarization is built up. A modification of this equation is also given, which takes into account moderate trapping of resonance radiation. An expression is also derived which relates the polarization of 3He to the intensity of the scattered pumping light.
A commercial Spectra Diode Laboratories, 1.083 μm diode laser has been used to efficiently spin polarize an atomic beam of He(2$\sp3$S) metastable atoms by optical pumping on the $\rm 2\sp3S\sb1\rightarrow2\sp3P\sb1$ (D1) transition. The diode laser is an InGaAs/GaAs strained multiquantum well with a distributed Bragg reflector to insure single longitudinal mode operation. The laser has been frequency stabilized to less than 1 MHz/hr drift. The helium metastable atom beam is produced by electron impact and the polarization is measured using a Stern-Gerlach analyzer. Atomic polarizations exceeding 97% have been obtained with $\sim$25 mW of power from the diode laser. A number of experiments currently under construction may also make use of the diode laser. These include the production of a spin polarized helium ion beam by optically pumping the metastable atoms in an rf discharge, and the trapping of helium metastable atoms in a magneto-optical trap (MOT).
The 3P2 metastable atoms of neon have been optically oriented. This represents the first case of the optical pumping of non-S state atoms. The optical-pumping process is described, and depolarization cross sections for collisions with ground-state neon and ground-state helium atoms measured. The cross section for collisional depolarization with helium is 4.30 \ifmmode\pm\else\textpm\fi{} 0.22 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ cm2, and with neon is 166 \ifmmode\pm\else\textpm\fi{} 8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ cm2 at 300\ifmmode^\circ\else\textdegree\fi{}K. The metastable 3P2 atoms of Ar and Xe have also been optically pumped. As the polarizability of the noble-gas buffer increases, the collisional depolarization cross section approaches the diffusion cross section.