B.S.T.J. Briefs: A Gas Lens Using Unlike, Counter-Flowing Gases

T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , J U L Y 19G-t A Gas Lens Using Unlike, Counter-Flowing Gases By D. W. B E R R E M A N (Manuscript received May 26,1964) Because of the current interest in gas lenses for possibe use in longdistance laser beam transmission, it seems worthwhile to report on the successful operation of an example of another class of gas lenses. This class of lenses utilizes the difference of specific refractive index of different gases to achieve focusing in a region where there is a variation in relative concentration of different gases. In the device to be described, two gases flow together continuously from opposing tubes into a mixing chamber. The chamber is designed so that the effective interface where the gases meet is an axially symmetric curved surface, which acts as a lens for light passing down the axis of the opposing tubes. In order to minimize distortion due to gravitational force, it is desirable to use two gases of about the same density. It may be most economical to separate and recycle the gases after they have run together. In principle, continuous separation with a semipermeable membrane would consume only a moderate amount of power. Except for a computation of the theoretical minimum of power consumption, no further discussion of the problem of gas separation will be presented in this paper. A working model of a single element of a counter-flowing gas lens is shown in Fig. 1. Rather elaborate precautions were taken to avoid HIGH INDEX LOW INDEX Fig.