Discharge characteristics at high repetition rate in longitudinally excited CO₂ laser pumped by fast pulsed discharge

In a previous study, we considered that the laser characteristics of longitudinal discharge pumped CO₂ lasers with fast pulse discharge were affected by changes in the discharge characteristics due to operations with high repetition rates. However, the discharge form has not been investigated in detail. In this study, the effects of repetition rate and gas pressure on the discharge were investigated by observing the discharge using a Pyrex discharge tube with an inner diameter of 12.6 mm and, length of 470 mm, and a CO₂/N₂/He gas mixture ratio of 1:1:2. At repetition rates of 150 Hz or lower, the discharge was uniform throughout the inner diameter of the discharge tube, whereas at repetition rates of 200 Hz or higher, the discharge contracted. The contracted discharge is thought to be caused by the residual charged particles generated by the discharge. At a high repetition rate, the discharge current density changes owing to the contraction of the discharge, which affects the optimal gas pressure and laser output energy. These findings are important for establishing the optimal operating conditions for longitudinally excited CO₂ lasers pumped by fast pulsed discharges.