A circuit for direct registration of electron densities measured interferometrically

Electron densities are commonly measured by determining the plasma refractive index with an interferometer. The circuit described permits the electron density to be recorded directly as a function of time. For the 6328 AA line of a He-Ne laser, the device has a sensitivity of 3.56*1018 electrons cm-2 V-1 and a resolving time of the order of 40 ns.