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Sensing Of High Pressure By Shock Heating Quartz Optical Fibers

We report the use of bare optical fibers to detect shock arrival times and shock pressures in the collision of a moving flyer plate with a stationary plate. Glass fibers were either laid on the surface of the stationary plate or put through closely fitting holes so that they were perpendicular to the plate, with their cleaved ends flush with the surface being struck by the flyer. The flyer, moving at 5 km/s, struck the stationary plate at an angle of 6.7°. The phase velocity of the line of Intersection, measured from the times of light onset in fibers at different positions, moved at over 40 km/s along the direction of the surface fibers. All of the fibers were shock heated to about 3600K, producing enough light to allow detection by optical receivers viewing the other ends of the fibers. By being reasonably careful about calibrating the absolute transmission of the optical system, we were able to obtain good estimates of the quartz temperature and pressure as a function of time and position along the surface fibers. (We assume that only the light from near the shock front emerges.) By fusing a short piece of smaller-core-fiber to the end of a surface fiber, we were able to get two signals from one fiber and deduce an instantaneous phase velocity. The perpendicular fibers gave understandable signals only during the time the shock ran through the stationary plate.