High‐power, twin‐frequency FIR lasers for plasma diagnostic applications

• Published in: Review of scientific instruments 1986-08, Vol.57 (8), p.1986-1988
• Main Authors: Lehecka, T., Savage, R., Dworak, R., Peebles, W. A., Luhmann, N. C., Semet, A.
• Format: Article
• Language: English
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1139202

The development of imaging interferometry and multichannel heterodyne scattering systems for fusion plasma diagnosis has dictated the development of high‐power, stable twin‐frequency sources in the 100→1000 μm spectral region. Output powers of 500 mW (185 μm), 150 mW (393 μm), 100 mW (496 μm), and 25 mW (1.22 mm) have been measured directly on a Scientech Calorimeter applying no correction factors. These powers have been achieved via the optimization of the CO2 and far infrared (FIR) laser cavities together with the use of buffer gases (to relieve bottlenecking) and variation of the pumped molecular gas temperature (to optimize the ground‐state population). The source intermediate frequency (IF) jitter in twin‐frequency FIR laser systems has also been investigated in detail. The effect of CO2 and FIR feedback on the IF frequency has been studied with the view of producing low‐cost stable laser systems without complicated a c t i v e stabilization. Finally a comparison between a novel twin‐frequency laser involving a s i n g l e optical cavity and a conventional system involving two separate cavities has been performed. The conclusions drawn from the above studies have been utilized in the design of laser systems operational on the TEXT tokamak and at UCLA.