Plasma Lens for Optical Path Difference Control

Abstract

This research investigated the feasibility of a plasma lens for wavefront 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 at optical glass at its ends. Air in the glass cylinder was ionized using a dielectric barrier discharge (DBD). The wavefront distortion produced by the ionized air was characterized by placing the plasma lens in one leg of a Michelson interferometer setup. The eect of gas pressure and plasma power were investigated. The results were compared to a derived analytic model that related the electron density and optical path dierence (OPD) to the plasma power. The agreement between the experiment and analytic model was very good, especially at the higher plasma power levels. The maximum OPD increased with the gas pressure inside the lens. A maximum OPD of approximately 1.5 µm was achieved in the experiments. This brackets OPD levels that are typical of aero-optic applications, and otherwise corrected using electro-mechanical 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 OPD levels and provide greater dynamic range.

The future for plasma science and technology

“…This would allow not only a variety of new focusing configurations, but also enabling new applications in communications, sensing, and imaging (super lensing, near‐field imaging and amplification, cavity super‐resonance, highly selective frequency filters, focusing and expanding devices) . The use of plasma elements in optical communications certainly requires further development in the miniaturization of appropriate plasma sources, and operation at atmospheric pressures …”

White paper on the future of plasma science for optics and glass

“…An ionized gas can therefore be utilized for rapid production of the required OPD, due to the very fast response of electrons to external fields. The most simple adaptive optical element, a plasma lens, can be realized using an axially symmetric (cylindrical) discharge in which the density of electrons and thus the OPD can be controlled by an external applied voltage . An addressable array of such lenses covering a solid state mirror could be used to form a plasma‐based wavefront correction device, a plasma adaptive mirror, whose frequency response would be limited only by the plasma on/off times of the individual elements …”

Computational hydrodynamics and optical performance of inductively-coupled plasma adaptive lenses

“…In plasmas, a tunable refractive-index distribution can be achieved through concentration gradients in the population of free electrons. 7,[9][10][11][12][13][14][15] A brief explanation of this phenomenon is provided below.…”

“…The effects described above have been exploited in recent experiments [12][13][14][15] to manipulate light through capacitively coupled plasma lenses for aero-optical applications in the mTorr-pressure range. In the present study, however, focus is made on inductive coupling at near-atmospheric pressures.…”