Experimental estimation of CO concentration in LN2 cooled CW CO laser operating with CO2 laser gas mixture

Abstract

The lasing medium of cryo-cooled CW-CO laser operated with CO2 laser gain medium (CO2–N2–He mixture) resulting in 5 µm emission is formed in-situ in the discharge and its composition, that is sensitively dependent on the discharge temperature, is not known a priori. The composition of the CO lasing gas mixture here was successfully arrived at by way of sampling the gas mixture at the exhaust and measuring the wavelength dependent absorbance by a Fourier Transform Infrared Spectrophotometer. This enabled us to determine the CO and CO2 concentrations in the lasing mixture accurately while the other major constituents were estimated from the initial partial pressures. The composition of the lasing gas mixture was studied for various discharge wall temperatures starting from no cooling condition (∼351 K) to LN2 cooled conditions (79 K). While the concentrations of both, CO2 and CO were found to decrease for temperatures below the freezing point of CO2 at the operating pressure of 11 mbar, the relative concentration of CO with respect to CO2 also increased with reducing temperature accompanied by a steady increase in the CO laser power output. The onset of lasing in 5 µm region was found to occur at a discharge wall temperature of 212 K.