Abstract

Far-infrared (FIR) cw laser radiation of 1.25 W has been obtained at the 119-μm (2522.8-GHz) methanol line with a CO₂ input pump power of 115 W. This is the highest power and conversion efficiency reported to this date on this transition. The frequency drift of the free-running laser is less than ±200 kHz ph. The improved performance of the FIR laser was achieved by (1) using reflecting optics wherever possible to minimize CO₂ mode degradation caused by damaged antireflection coating of transmitting optics; (2) enclosing the input and output assemblies within the lasing medium to minimize the external effects on the cavity length as well as eliminating the mechanical instabilities associated with the use of bellows; (3) cooling the resonator wall to 0 °C and adding He as the buffer gas. The combined pressure of CH₃OH and He was 500 mm Hg. We believe that the major source of the laser frequency drift is thermal in nature and an active thermal stabilization scheme should further improve the frequency stability of the laser. This laser, which has also been tested at other frequencies ranging from 600 GHz to over 3000 GHz with improved results, will prove to be essential in generating tunable laser sidebands for spectroscopic measurements or other experiments which require a frequency stable FIR source.

© 1986 Optical Society of America