Mode and frequency control of compact CO₂ slab lasers through intracavity coherent imaging

The operation of a compact slab-waveguide CO₂ laser at multimode output power levels of 90 W with greater than 14% efficiency was demonstrated. This is about five times the power per unit package length obtainable in typical square-bore waveguide lasers without resorting to complicated folded designs. A detailed modal study of the laser, as the resonator was scanned through a free spectral range, implied that the simultaneous existence of two or more modes in the output was ordinary for this simple multimode resonator design though oscillation was on a single laser line. By comparison, both single-mode and single-frequency operation was demonstrated by using an intracavity wire grid whose dimensions were selected to meet the needs of the waveguide-confined Talbot effect. A single-mode output power greater than 70% of the multimode system emission was obtained.