Dual far infrared laser diagnostic of magnetized plasmas

A dual far infrared laser has been constructed and its properties have been exploited to probe tokamaklike discharges in the CDX toroidal device. Thermal variation of the difference frequency between the two far infrared cavities is slow, although the cavities lack thermal stabilization, simply because their assembly on the same chassis exposes them to virtually identical temperature changes. The optical arrangement beyond the laser permits conversion within minutes between interferometry and density fluctuation observation, and within an hour between different operating wavelengths. Line average densities of 2 x 10(13) cm(-3) and coherent fluctuations in the neighborhood of 20 kHz have been measured with this diagnostic.