Gain measurements of longitudinally excited CO₂ laser using low-pressure gas without helium

The gain characteristics of a CO₂ laser pumped by a longitudinal pulsed discharge were investigated to develop a compact He-free CO₂ laser operating at a high repetition rate. The longitudinal discharge tube had an inner diameter of 0.8 cm and a length of 45 cm. High-voltage pulses with a discharge starting voltage of 13.4–30.2 kV at a rise time of about 321 ns were applied to the discharge tube. CO₂/N₂ mixture gas with mixing ratios of 1:0, 1:1, 1:2 and 1:3 was used. The small signal gain coefficient was measured by inputting a seed CO₂ laser pulse into the longitudinal discharge tube. The small signal gain coefficient depended on the delay time between the start of the discharge in the longitudinal discharge tube and the input of a seed CO₂ laser pulse, the gas mixing ratio, the gas pressure, the repetition rate and the input energy to the longitudinal discharge tube. In this work, in He-free gas, the maximum small signal gain coefficient at a repetition rate of 300 Hz was 2.11%/cm with a delay time of 30.4 μs, a CO₂/N₂ gas mixing ratio of 1:2, a gas pressure of 2.6 kPa and an input energy of 191 mJ.