Submillimeter–far-infrared spectroscopy in the liquid and solid states with a tunable optically pumped laser*

The design and spectroscopic application of a submillimeter–far-infrared (FIR) optically pumped tunable laser are described. Driven by 15–25 W of power from a cw CO2 laser, the FIR system gave milliwatts of power between 96 and 1217 μm. The pumped media were methyl alcohol (CH3OH) and 1,1-difluoroethylene (CH2CF2). The laser spectrometer was used to measure the transmission of liquid H2O, the bulk semiconductor GaAs, the epitaxial semiconductor InAs, and the high-temperature superconductor V3Si. In general, the laser system gave vastly improved signal-to-noise ratios, reduced stray light problems, and increased penetration power relative to more conventional FIR spectrometers. The laser results agreed extremely well with results from conventional spectrometers except where the narrowness of the laser line produced interference effects.