Pressure dependence of copper laser output characteristics

Output characteristics of a large-bore (8-cm-diameter) copper laser were analyzed at different neon pressures. Radial delay decreased from ∼40 ns at 30 Torr to ∼10 ns at 110 Torr because of increased plasma impedance. When the laser was running as an amplifier, the best power was achieved at approximately 80 Torr (small-bore copper lasers normally optimize at 30-40 Torr). This occurs because a more pronounced reduction of radial delay at higher pressures can be achieved in large-bore devices. As a result, a more uniform beam profile was obtained at higher pressures because of more efficient axial pumping. The improved coupling between the laser head and the pulse modulator at higher pressures also translates to a substantial improvement in laser efficiency (>50%) as the pressure rises from 30 to 100 Torr. The same laser optimizes at a much lower pressure (30-40 Torr) when its energy is extracted with a flat-flat resonator, because resonator loss increases with increasing gas pressure because of faster gain rise time at higher pressures.