This book describes a new technique for varying the power output from far-infrared gas lasers. It presents the design and construction details for these lasers, including the advantages of using a Michelson interferometer configuration with a polyethylene or polypropylene beam splitter. The book discusses the method's advantages over traditional hole-coupling schemes and provides tables of power outputs obtained from various lasers using this coupling method. The author provides construction notes and detailed drawings for the laser, including information on vacuum seals, mirror mounts, and the beam splitter. The book concludes with an alignment procedure and a discussion of the laser's significance in simplifying line identification and providing a linearly polarized output beam.