High power, twin frequency FIR lasers for plasma diagnostic application

The development of imaging interferometry and multichannel heterodyne scattering systems for fusion plasma diagnosis has dicated the development of high power, stable twin frequency sources in the 100 μm → 1000 μm spectral region. Output powers of 500mW (185 μm), 150mW (393 μm), 100mW (496 μm), and 25mW (1.22mm) have been measured directly on a calorimeter applying no correction factors. These powers have been achieved via the optimization of the CO2 and FIR laser cavities together with the use of buffer gases (to relative bottlenecking) and variation of the pumped molecular gas temperature (to optimize the groundstate population). The source IF jitter on 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 active stabilization. A comparison between a novel twin frequency laser involving a single optical cavity and a conventional system involving two separate cavities has been performed. The conclusions from these studies are discussed. They have been utilized in the design of laser systems operational on the TEXT tokamak and at UCLA