Low-Temperature Performance of Roto-Vibrational Molecular Lasers

Abstract

The development of new lasers in the mid-infrared spectral region (10-30µm) is becoming increasingly important for studies of photochemical processes based on the selective vibrational excitation of molecules. The laser-pumped roto-vibrational molecular lasers (OPML’s) operate in the mid-infrared and are capable of generating the high intensities required for many photochemical studies. Recent experimental results have demonstrated that by operating optically pumped roto-vibrational molecular lasers at low temperatures, their performance can be greatly improved [1,2,3,4,5]. In this paper a liquid nitrogen (LN₂) cooled OPML cell is described, and the performance of the device is illustrated through a parametric study of two OPMLs pumped by a CO₂ laser, the carbonyl sulphide (OCS) 19 µm laser [6] pumped by the P(22) 9.2 µm line and the ‘Freon 14’ (CF₄) 16 µm laser [3] pumped by the R(12) 9.6 µm line. For the OCS laser we report the highest output energy and for both lasers the highest operating pressures. These results were achieved at the lowest operating temperatures consistent with the vapour pressure limitations of the lasant gas.