Tunable terahertz gas laser based on a germanium spectrum splitter

A tunable terahertz gas laser is demonstrated with a germanium ealton served as the spectrum splitter. The germanium ealton is 1.2-mm thick and anti-reflection coated at 10.17 μm, giving good dichroic performance for infrared and far-infrared radiation. By tuning the incident angle of the germanium ealton, the transmittance of 95% at 9– 11 μm wavelengths and the reflectance of more than 70% at 180 – 500 μm wavelengths can be achieved simultaneously. Based on the germanium ealton, a tunable CH₃F gas laser is presented when pumped by a transversely excited atmospheric CO₂ laser. By tuning the pump lines and the incident angles, four THz laser wavelengths are obtained including 181 μm, 261 μm, 360 μm and 496 μm. The energy conversion efficiency is in the order of 10^–3, which is comparable to those of typical efficient CH₃F molecule lasers. The germanium ealton is anticipated to be an efficient dichroic element for terahertz gas lasers with different wavelengths.