Dynamics of a Discharge-Excited CO₂ Lasers

A tunable diode laser (TDL) operating in the region of 2150 to 2350 cm⁻¹ wavenumber is used in this work to investigate the dynamics of level populations in CO₂ lasers. The wide tunability of the TDL is exploited in determining the populations in any level of the CO₂ molecule. Thus, the vibrational population distributions in a CW CO₂ laser discharge under both lasing and non-lasing conditions are measured and are compared with the mode temperature model. The relaxation processes associated with the upper and lower levels of CO₂ lasers are also investigated. In particular, the electron excitation and de-excitation rates of the upper laser level in typical CO₂ discharges are determined directly from the experiment, and it is shown that electron de-excitation is responsible for the saturation of v₃ mode temperature in electrically excited CO₂ lasers at high discharge currents, and imposes a fundamental limitation on the gain attainable in CO₂ lasers. The relaxation of the lower laser level is complicated by the occurrence of several competitive vibration-vibration (V-V) processes. The TDL measurements enable us, for the first time, to monitor separately the population in all levels of concern to the relaxation of the lower laser level and to determine the rate constant of each of the available decay channels. It is shown that the O2²O level plays an important role in the relaxation of the lower laser level. Doctor of Philosophy (PhD)