Development of short-wavelength far-infrared laser for high density plasma diagnostics

For high density operation of the large helical device and for a future large plasma machine such as ITER, a powerful 57 μm CH3OD laser pumped by a continuous wave 9R(8) CO2 laser has been developed. The 57 μm (5.2 THz) laser light has been successfully detected by using a GaAs Schottky barrier diode detector with a corner reflector. For optical windows of the plasma vessel and the far-infrared laser crystal quartz etalons have been designed under a concept of a two-wavelength etalon for 119 and 57 μm lights.