Polarization measurement on spectral lines of low intensity and short duration

Measurement of the polarization of spectral lines emitted from a plasma in a magnetic field can give valuable information about the anisotropy of the electron velocity distribution. Practically, this means measurement of the polarization of a weak, moving three-dimensional light source of short duration. Careful design and adjustment of the optical and photoelectric equipment is necessary to avoid sources of systematic error. The design and optimization of the equipment is discussed in detail. Measurements have been made on helium lines at a helium density of about 1020 m-3 (3 mTorr).