A vibration compensated high frequency heterodyne CO2laser interferometer for plasma diagnostics

A CO 2 laser interferometer has been developed for electron density and density fluctuation measurements in the new and larger reversed field pinch plasmas. (Density range 2*10 19 to 2*10 21 electrons m -3 plasma minor radii 0.26 and 0.6 m.) The instrument incorporates an acousto-optic modulator to produce the 40 MHz intermediate frequency for heterodyne detection and uses a common path, visible HeNe laser interferometer, based on the same heterodyne technique, to monitor vibration of the optical components. The system has been demonstrated by measuring the rapid rise and decay of the electron density in a small Z-pinch plasma in the presence of induced vibration.