Perturbation theoretical analysis and its application for TM010-mode microwave cavity of a gas laser

An analytical expression and a perturbation formula for the cavity resonant frequency dependence of plasma are derived for the cylindrical TM010-microwave plasma cavity. A comparison between the exact and the approximate solution shows that the perturbation theory can be used accurately to analyze the perturbation effect on the cavity resonant frequency caused by microwave plasma in low pressure microwave excited gas lasers. A new method is proposed to prevent detuning of the cavity by the perturbation of the plasma and glass tube, so that a uniform and steady-state microwave plasma is successfully formed and a stable laser output power is also obtained. The electron density and the microwave dielectric constant of a tube shell can be measured by the perturbation approach.