Powerful 48-and 57-µm CH 3 OD lasers pumped by a 9R(8) CO 2 laser have been developed to establish a new two-color FIR laser interferometer system for high density and large volume plasma diagnostics. To design the collimated beams for the interferometer, the beam profiles and the divergence angles have been measured for the 48-and 57-µm CH 3 OD lasers oscillated simultaneously. Water vapor absorptions for the laser wavelengths have been measured at 22 • C to realize an efficient transmission line. Optical constants and transmittance and reflectance of crystal quartz, silicon, CVD-diamond, polyethylene sheet, Mylar film, TPX plate, metal mesh and wire grid have been measured to design the optical components (observation windows and beam splitters) in the 48-and 57-µm laser interferometer system.

Carbothermic reduction of magnetite in a 2.45-GHz microwave multimode furnace was investigated with multipoint pyrometric and spectroscopic measurements. Both experimental results emphasize the importance of surface heating of the specimen by microwave-generated plasma for reducing iron oxide. The pyrometric observation shows a shift of the heating mode from the direct volumetric heating by microwave to the surface heating by microwave-generated plasma, when the temperature of the material suddenly rises from ∼800 to ∼ 1000 • C accompanied by light emission from plasma. The emission spectrum in the near-UV range (240-310 nm) changes drastically from a continuous spectrum to a line emission spectrum of iron, representing progress of carbothermic reduction of iron oxide. The multipoint spectroscopic observation indicates extensive carbothermic reduction occurring on the entire upper surface of the specimen.

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A two-color interferometer system using 48and 57-gm CH30D lasers pumped by a continuous-wave (cw) 9R(8) C02 laser have been developed to measure electron density profiles of large plasma devices. To test this system, the Michelson interferometer of one channel has been constructed on a test bench. We have obtained preliminary interference signals from the two-color interferometer system.

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