Fluid mechanical light guide.
It is shown that a beam of light can be deflected continuously through large angles along a curved path using the gas flow from a convergent-divergent nozzle sector whose throat lies on the arc of a circle. The amount of deflection depends on the included angle of the nozzle sector and on the density gradients created by the expanding gas flow. For a 360 degrees included angle the beam can in principle be bent into a closed path with a radius of the order of a few tens of centimeters: Nozzle sectors with included angles of 30 degrees and 180 degrees are studied both theoretically and experimentally. It is demonstrated that a well-defined region exists in the flow wherein light rays are trapped in near-circular paths whose radii are close to the radius of the nozzle throat. The trapping region in effect constitutes a curved light guide. Very low light losses are predicted and measured, even for large deflections. Using nitrogen at a stagnation pressure of 110 atm as the working fluid, a laser beam is deflected as much as 180 degrees with a transmission approaching 100%.
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Christiansen
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Bruckner