Plasma Diagnosis by Means of Optical Scattering

When a pulse of intense light from a laser passes through a plasma, a very small fraction of the light is scattered out of the beam by free electrons. Measurements of the intensity and spectral distribution of the scattered light can be related to the electron density and velocity distribution in the plasma. This paper presents a general discussion of the use of optical scattering as a plasma diagnostic technique. Applicability to various experimental situations is discussed, and considerations of interest in the design of diagnostic apparatus are presented.An apparatus has been constructed for the measurement of electron density in cold plasma. The apparatus is described in some detail. Typical results are given for densities as low as 1013 electrons/cm3.