Design and operation of a two-color, four-beam fiber optic interferometer

Summary form only given, as follows. A novel two-color, four-beam fiber optic interferometer (FOI) has been designed and built. This instrument is unique because it uses standard fiber optic components in its construction, which allows for an inexpensive yet sophisticated design. Wavelength division multiplexers are used to combine two separated wavelengths, 1550 nm and 1310 nm, into a single fiber, which is then fed to a collimator and passed through the medium to be measured. Four independent beams of two colors each are available in the instrument. Each color and beam uses a feedback loop to drive a piezo-electric fiber stretcher (total of eight) to counter the effects of acoustic vibrations. The use of two wavelengths allows both the electron density and the neutral density to be measured simultaneously. The design sensitivity of the instrument is less than 7/spl times/10/sup 13/ cm/sup -2/ for electrons and less than 6/spl times/10/sup 15/ m/sup -2/ for neutrals. Sample data is presented which show the results of measurements preformed on pre-ionized gas puff valves and opening switch plasmas.