Just What Is

Optical Pumping

  • In this experiment, we optically pump 5S(1/2)Rb with 795 nm, circularly polarized light to a polarized state. Under radiative decays, spin -(1/2) Rb is excited to this metastable 5P(1/2) state by the incoming photons. As governed by the polarization ratio, one-third of which return to their original state, the rest are sent to a spin +(1/2) state. Most undergoe Non-Radiative Decay; they are first excited to the P(1/2) state, exhibit collisional mixing, and return back to the S(1/2) state. Eventually, a all end up in the S(1/2) (+1/2)-spin state.

  • Next, as governed by the hyperfine interaction of the Rb polarized elctron's wavefunction and the He3 nuclear's wavefunction, the polarized Rb electron interacts with the He3 nuclear via. spin-exchange. This means that when encountered with a He3 nuclear, whoes spin is 'anitparallel' to that of the Rb, the spin directions are exchanged....else nothing happens.

    (/|\)Rb + (\|/)He -> (\|/)Rb + (/|\)He

  • The result: Polarized He3, which is used to polarize the beam of neutrons. He3 strongly absorbs neutrons of opposite spin through a broad resonance. Since neutrons of parallel spin with the He3 weakly interact with He3, what is left is a beam of neutrons polarized parallel to that of the already polarized He3.