Skip to main content

Analysis of a Tubular Gas Lens

01 July 1964

New Image

A communications system using light as the carrier of intelligence needs an efficient medium to propagate light from transmitter to receiver. Among the several alternatives, the idea of Goubau and Schwering1 of confining and propagating an electromagnetic wave with a system of lenses appears promising. However, in a lens-waveguide system there is a wide range of possibilities as to what types of lenses to use. Conventional glass lenses present problems, since they may not only absorb light in the glass medium itself, but furthermore present important reflection losses which can be only partially avoided by special techniques such as coating the lens surfaces or making use of the Brewster angle. 1759 1772 THE HELL S Y S T E M T E C H N I C A L J O U R N A L , J U L Y 19(34 Even if such corrective measures are used, there is still residual reflection and scattering of light due to unavoidable surface irregularities. It appears that most of the problems connected with glass lenses could be overcome if, instead of a high-index medium such as glass, a very lowindex focusing medium were used. If the transition from air into a dense medium could be avoided, the problem of light reflection would not exist. Gases present themselves as an obvious choice of a low-index dielectric medium. Their dielectric constant can be influenced by changing their density. A change of density is most easily effected by varying the gas temperature. D. W. Berreman 2 built a successful gas lens by maintaining a temperature gradient between a hot helix and a cold cylindrical enclosure.