Method of electron density measurement by Fabry-Perot interferometry

A method for determining the electron density of thin plasma by means of Fabry-Perot interferometry is proposed. The interferometer consists of two plasma layers and dielectric material surrounded by two plasma layers. The electromagnetic wave transmittance and Fabry-Perot resonances for the interferometer are calculated. It is shown that the plasma density can be determined from the measurement of the resonance frequencies. This is also applicable to the conduction electron density measurement for semiconductor films.