B.S.T.J. Briefs: A Lens or Light Guide Using Convectively Distorted Thermal Gradients in Gases

Development of systems for long-distance communications using laser beams is of considerable current interest. A major problem is to avoid losses in transmission systems for light. Losses by scattering and absorption in solid transmission schemes are likely to be large. By using gases as the media t h a t guide the light beam, such losses should be minimized. A number of schemes in which gases can be made to guide a light beam have recently been investigated. Tests on models of one type of gas lens or light guide utilizing refractive index gradients caused by temperature gradients are to be described in this paper. These particular models consisted of a suitably shaped continuous heating element or train of separate elements supported by insulating material inside a cooler pipe. Heating elements composed either of a series of closely spaced, doughnut-shaped rings or toruses, or of a single, continuous helix of suitable dimensions were used in the experiments to be described. T h e beam travels through the doughnut holes or down the axis of the helix. Helices were used in the more detailed tests to be reported here because they are much easier to construct and to support in the cooler outer jacket. T h e y focus at least as strongly and with as little aberration as toruses of approximately equivalent dimensions. Lens trains of the types described focus to some extent by the alternating gradient (AG) focusing mechanism.* 1 , 2 However, if the temperature distribution is suitably distorted by moving the gas past the heating element, a great enhancement of focusing can be obtained.