Brian Neiswander

Plasma Lens for Optical Path Difference Control

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.

Geometric Optimization of a Cylindrical Plasma Adaptive Optics Lens

Plasma is a dynamic optical medium with potential applications in the field of aero-optics for wavefront control. The objective is to develop “plasma adaptive optic” devices which rely upon the relationship between plasma electron density and index of refraction. The advantages of plasma adaptive optic devices are that they have no moving parts and can have temporal responses two orders of magnitude higher than the fastest deformable mirror. Therefore, plasma adaptive optic devices have the potential to be more robust, less subject to fatigue, and faster than conventional technology. Experimental results and a theoretical model are presented which investigate the spatial distribution of the plasma inside a cylindrical plasma adaptive optic lens. The experiment reveals two distinct plasma formation regimes that occur depending on the lens geometry. The theoretical model is used to help identify the geometric parameters required to produce each plasma regime. The excellent agreement between the experiment a...

Plasma Adaptive Optics Evaluation Using Two-Wavelength Heterodyne Interferometry

The third part of a research program that investigates the possibility of using low-temperature ionized air (plasma) for adaptive optics in an airborne laser directed-energy system is presented. It...

Electromagnetic wave transmittance control using self-organized plasma lattice metamaterial

A reconfigurable glow discharge plasma lattice structure is examined for its ability to interact with and suppress electromagnetic (EM) wave energy with wavelengths on the order of centimeters. The plasma lattice is formed in the air gap between a double dielectric electrode arrangement that formed a rectangular cross-section channel. The lattice consists of columns that span the gap between the electrodes. The spacing between the plasma columns in the lattice results from a surface charge instability that is controllable by a combination of channel height, AC voltage, and gas pressure. The lattice number is highly repeatable and predictable following packing theory. The effect of the plasma lattice spacing on the transmittance of O(cm) wavelength EM waves was investigated. Excellent agreement was found between the experiments and simulations, with S21 transmittance reduced by up to 75%. In addition, experiments in which the EM waves were oriented at an oblique angle to the plasma lattice incident axis were performed. This documented a narrow-band absorption that was predicted from an anisotropic medium permittivity tensor analysis. These experiments also indicated a negative index of refraction of the oblique EM waves for the plasma lattice that provided further evidence of its anisotropic behavior.A reconfigurable glow discharge plasma lattice structure is examined for its ability to interact with and suppress electromagnetic (EM) wave energy with wavelengths on the order of centimeters. The plasma lattice is formed in the air gap between a double dielectric electrode arrangement that formed a rectangular cross-section channel. The lattice consists of columns that span the gap between the electrodes. The spacing between the plasma columns in the lattice results from a surface charge instability that is controllable by a combination of channel height, AC voltage, and gas pressure. The lattice number is highly repeatable and predictable following packing theory. The effect of the plasma lattice spacing on the transmittance of O(cm) wavelength EM waves was investigated. Excellent agreement was found between the experiments and simulations, with S21 transmittance reduced by up to 75%. In addition, experiments in which the EM waves were oriented at an oblique angle to the plasma lattice incident axis ...