Development of Polarized High-Energy Photon Beams using Coherent Bremsstrahlung

Mesons are produced in the GlueX detector at Jefferson Laboratory from collisions between a high-energy gamma ray beam and protons in a liquid hydrogen target. In creating gamma rays through bremsstrahlung, X-rays are also produced, which limit how intensite the photon beam can be without overwhelming the capabilities of the electronics to handle the signal rates. We designed a small, lightweight grazing-incidence mirror that reflects X-rays while remaining transparent to higher-energy gamma rays. The mirror must be sufficiently smooth and planar, capable of filtering out X-rays while keeping its thickness minimal, on the order of one micron. We devised a plan to use differential thermal expansion between an aluminum foil and its mount to control the tension and minimize the surface roughness of the aluminum mirror. To test how aluminum foil behaves under high tension compared to our calculated expectations, we applied tension to standard aluminum foil mechanically. We developed a strategy to use the acoustic resonances of the aluminum membrane in different vibrational modes to determine the tension based on the frequencies at which the surface exhibits distinct symmetric oscillatory motion.