Effect of Gas-Flow Velocity on Transient Behavior of Gain Constant in a Fast-Axial Flow Type CO2 Laser Amplifier

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Abstract
Depending on the gas-flow velocity v together with the discharge current I dis, the decrease of an output power amplified through a fast-axial flow type (FAF) CO2 laser amplifier has been observed within a few minutes after discharging its plasma tubes. Taking into account the effects of v and/or I dis on the gas temperature, the pumping rate to the upper laser level and the dissociation of a CO2 molecule, the gain constant is formulated as a function of discharge time for a partially homogeneously broadened laser medium at individual vibrational-rotational transitions, under the conditions of the small-signal approximation and the resonant amplification. The experimentally determined small-signal gain is compared with the theoretical estimate based on the above formulation, being in good agreement with each other. Resultantly, the dependences of the observed power decrease and transient time to have a stable output power upon v with I dis are also compared with the calculations and found to be consistent.