4.3-μm TE CO₂ Laser Dynamics

Abstract

<p>This thesis describes a detailed study of the dynamics of the 4.3-μm CO₂ laser. Pulsed laser action at 4.3-μm its achieved by using a 10.4-μm sequence CO₂ laser to optically pump CO₂ molecules which have been excited in a discharge. Quantitative data regarding the processes involved in 4.3-μm lasing are presented, and techniques for optimization of performance are described. Single-line output energies of 15 mJ/pulse and peak powers of 100 kW/pulse are obtained using a conventional transversely-excited (TE) CO₂ discharge 88 cm in length. Furthermore, it is shown that pulse energies are scalable to several hundred millijoules.</p> <p>The construction of a high power sequence CO₂ pump laser is discussed in detail. The laser utilizes an atmospheric pressure TE discharge 88-cm long and an intracavity hot CO₂ cell. Output energies of up to 6 J/pulse are obtained. Other work involves the characterization of discharge-excited CO₂ and the optimization of discharge operation. Several discharge parameters are measured including mode temperatures, collision-broadened linewidths, and overlapping gain and absorption coefficients. These measurements provide accurate input data for a rate-equation model of the 4.3-μm laser.</p> <p>The study of 4.3-μm dynamics involves extensive measurements of small-signal gain and energy extraction. By making quantitative comparisons between these measurements and the rate-equation model, the influence of various parameters on the operation of 4.3-μm lasers is examined. The factors which dominate the dynamics of 4.3-μm lasers are found to be the short collisional lifetime of the 4.3-μm upper laser Ievel, the degree of discharge excitation, and the presence of interfering absorptions. As a result, efficient operation is restricted to discharge pressures below 100 Torr and CO₂ contents of less than 5 percent. The conditions which optimize performance are identified, and guidelines for scaling the 4.3-μm laser to higher pulse energies are presented.</p>