Plasma Lens for Optical Path Difference Control

Abstract

This research investigated the feasibility of a plasma lens for wave front control of coherent light sources. The approach is based on the relation between a plasma electron density and its index of refraction. The plasma was encapsulated in a hollow glass cylinder with flat optical glass at its ends. Air in the glass cylinder was ionized using a dielectric barrier discharge. The wave front distortion produced by the ionized air was characterized by placing the plasma lens in one arm of a Michelson interferometer setup. The effect of gas pressure and plasma power were investigated. The results were compared with a derived analytic model that related the electron density and optical path difference to the plasma power. The agreement between the experiment and analytic model was very good, especially at the higher plasma power levels. The maximum optical path difference increased with the gas pressure inside the lens. A maximum optical path difference of approximately 1.5 μm was achieved in the experiments. This brackets optical path difference levels that are typical of aero-optic applications, and otherwise corrected using electromechanical deformable mirrors. Although air was used as the gas in the plasma lens in these feasibility experiments, the use of Penning mixtures would further increase possible optical path difference levels and provide greater dynamic range.