Scaling and performance of CO₂ lasers at supra-atmospheric pressure

Abstract

The performance of a compact uv photo-preionized TE laser is studied in the pressure range 1–5 bar. As the pressure is increased, the laser pulse shape is little altered, but both the peak power and the total output pulse energy increase significantly with pressure, even for constant input electrical energy. For various gas mixtures and excitation source capacitors the measurements suggest approximate output energy scaling with the product of the source charge per unit electrode area [C.m⁻²] and the molecular partial pressure [CO₂+N₂+CO]. This is explained in terms of the pressure-dependent discharge impedance. An input-energy-related discharge instability limits the optimum laser pressure to 1.5–2.5 bar, and we show that, at constant input energy, the instability boundary depends on the molecular partial pressure alone. The pre-ionization photo-electron yield varies negligibly with pressure, but the discharge tolerance to added oxygen decreases asp ⁻³ top ⁻⁴, dependent on gas mixture. Nevertheless sealed operation for >10⁵ shots has been obtained with a 5% CO₂∶5% CO∶3% N₂∶2% H₂∶85% He gas mixture at a total pressure of 5 bar.