A FREQUENCY SHIFTED LASER INTERFEROMETER
The world's energy and associated political problems make controlled thermonuclear reactions an attractive national and international goal. Experiments in the magnetic confinement of plasmas are being made to study the conditions necessary for a fusion reaction. This paper deals with the design, construction, testing and utilization of a frequency shifted laser (He-Ne) interferometer designed for use on the topolotron, a pulsed plasma machine operated by the Physics Department of Brigham Young University. The interferometer provides a time history of the average electron density along a selected chord. The rms noise level of the interferometer is two degrees over a fifty-four microsecond time interval. The plasma and reference beams are optically heterodyned to produce an 80 MHz beat frequency which is phase modulated by changes in the plasma electron density. The modulated optical beat frequency is carried by an optical fiber into a low noise environment where the base band phase and amplitude information is recovered and displayed by a mini-computer.