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A light beam can be confined and guided along a straight or gently curved path through a gas by appropriate control of temperature gradients in the gas. Two types of guides that take advantage of convection to assist in this temperature control are described. One is composed of a continuous, warm, open helix within a cooler outer pipe containing the gas. The other is a series of gas lenses, in each of which the gas is warmed as it moves through an opposing pair of short focusing tubes to the base of a short warm chimney. The gas rises in the chimney and is then cooled, whereupon it falls through ducts that return it to the focusing tubes. Experiments were performed on each type and the relative merits of the two types are compared. An approximate mathematical analysis of the operation of the second type is presented.
Dwight W. Berreman (Mon,) studied this question.