A VARIABLE REFLECTIVITY OUTPUT COUPLER FOR OPTICALLY PUMPED FAR INFRARED-LASERS

In this paper we describe the design and performance of a variable reflectivity output coupler for optically pumped far infrared (FIR) lasers. The output coupler is a compact, tunable Michelson interferometer. The output coupling ratio (i.e. the Michelson transmission) is adjustable between 0 and greater-than-or-equal-to 60% for laser line wavelengths between 110 and 500-mu-m. This output coupler provides increased output power and flexibility, since it can be tuned to optimum coupling ratio for different laser lines. Beam profile measurements show that the Michelson output coupler produces a well collimated Gaussian laser beam. Design features are a) the use of a 10-mu-m reflection coated quartz vacuum window which acts as a dichroic mirror for the pump radiation and b) the high mechanical stability obtained by a leaf spring flexure mount of the movable Michelson mirror and by restricted alignment devices.