Investigation of a transverse-excited high-power CO2 laser

Abstract

Investigations of a high-power transverse-flow transverse-discharge closed-cycle cw CO2 laser, designed as a laboratory facility primarily for materials processing research, are reported. A self-sustained dc electric discharge between a multipin cathode (tungsten) and a planar anode (polished copper) has been used forexcitation of the working medium, a mixture of CO2, N2, and He. The discharge volume is 5 dm3. A controllable-speed centrifugal compressor circulated the gas at a pressure of ~ 80 kPa, with the mass flow rate reaching 0.5 kg s-1. The specific power per unit mass flow amounts to 200 kW/kg s-1. The discharge characteristics have been measured in various flow conditions to evaluate the effect of flow conditioning devices on the discharge stability. Various multipass unstable optical resonator configurations have been adopted based on previous numerical analyses. Measurements of small-signal gain distribution along the discharge channel (with a maximum of 1 m–1) allowed optimization of the resonator position relative to the discharge. The dependence of the output power on the electric power dissipated in the discharge was measured. For a two-pass resonator (M = 1.8 kanigen mirrors) with one amplifying pass, the maximum output beam power was 4.4 kW at an electro-optical efficiency of 10%. The beam divergence was ~2 times larger than the diffraction-limited value. This allowed satisfactory tests of laser welding and cutting. (Poster paper)