Dependence of Spatial Gain Distribution on Gas-Flow Velocity and Discharge Current in a Fast-Axial Flow CO2 Laser Amplifier

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Abstract
Taking into account the radial distributions of the gas-flow velocity v, the discharge current I dis, the gas temperature T and the effective pumping rate ηe, we theoretically derive the gain coefficient γ as a function of the radial distance from the plasma-tube axis for a fast-axial flow (FAF) CO2 laser amplifier. For various combinations of v and I dis, the calculated γ's are compared with the experimental results corresponding to both laminar and turbulent flows, resulting in good agreement in both cases. Increase of v leads to a linear enhancement of γ: for example, γ becomes about two times larger with increasing v from 80 to 180 m/s, while there is an optimum current near 45 mA to provide the highest gain in our FAF system. It is especially noteworthy that the high-gain region tends to spread towards an area far off-center of the discharge tube axis with increasing v, and its spreading area becomes significantly broader at a turbulent flow greater than v = 170 m/s.