B.S.T.J. Briefs: Gas Mixture Lens Measurements

Gas Mixture Lens Measurements By A. C. B E C K (Manuscript received June 15, 1964) Different gases have different refractive indexes. If two different gases are introduced into different parts of a straight hollow tube and allowed to continue in laminar flow, they diffuse into each other slowly hut remain sufficiently separated so that a refractive index gradient is maintained for some distance. It has been suggested by A. R. Hut-son, G. E. Conklin, and the author that various optical components such as prisms and lenses can be obtained by using such gaseous structures. These components have very low losses and reflections, with no solid surfaces to cause matching or cleaning problems. For these reasons they may have important applications in optical communications systems. 1,2,3 A simple structure, sketched in Fig. 1, was built to test this principle and to get some information about the performance of a gas mixture lens. A cylindrical porous-walled tube with an inside diameter of J inch and an exposed length of 3 inches was mounted inside a larger phenolic cylinder with its ends blocked to form a gas reservoir. A single-mode light beam from a helium-neon gas laser oscillating at A = 0.63 micron was collimated at a diameter of about | inch with glass lenses and then sent along the axis of the porous tube through which one gas was flowing. The second gas was introduced into the tube through the porous walls. The light beam was then intercepted on a screen about 10 to 20 feet away.