Development of a terahertz gas laser optically pumped by a mid-infrared quantum cascade laser

Abstract

A compact continuous-wave terahertz laser was realized by optically pumping 15NH3 with a mid-infrared Quantum cascade laser operating at room temperature. Three methods for the mid-infrared spectroscopy were studied in order to identify and characterize suitable gain media and pump transitions. Transmission spectroscopy with a microbolometer camera proved to be the best suited method for this purpose. Three molecular species that could be used as a gain media were studied. Saturation was detected for 15NH3 and several molecular resonances that could be used to get THz lasing were identified. A measurement routine that would allow to search for terahertz lasing was developed. As a result, laser emission was found for five transitions of 15NH3 producing radiation at 4.52 THz with up to 8 µW optical power and optical conversion efficiency of 4.2E-5 . The dependence of the acquired results on several important operating parameters (such as pressure, cavity length and pump power) was studied and possible ways for further improvements were suggested.