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1 January 1992 High-precision characterization of gas-filled shells using scanning Fabry-Perot interferometry
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The validity of inertial-fusion experiments relies on precise and accurate knowledge of the characteristics of small (<1-mm diam) gas-filled shells, such as the wall thickness and outer diameter of the spherical microballoon and the density of the gas inside it. In the past, dual-beam interferometry has been utilized to determine these quantities. These techniques produce interference patterns which have a spatial intensity distribution that is sinusoidal. In contrast, multiple-beam interferometry produces interferometric patterns which are described by the Airy function, and they can have interference maxima that are sharp and narrow, depending on the number of interfering wave fronts. This work describes a technique that uses a scanning, plane Fabry-Perot interferometer to determine inertial-fusion target parameters to high accuracy using the increased precision of multiple-beam interferometry. The microballoon is inserted between the highly-reflective surfaces of an air-spaced Fabry-Perot etalon that is illuminated with monochromatic plane waves. As the separation between the end mirrors is varied continuously, the intensities of the light transmitted through the center of the microballoon and passing external to it are recorded simultaneously as a function of mirror spacing. From this data, the phase difference between these two wave fronts is determined and the appropriate inertial-fusion target parameters are calculated. Using a scanning Fabry-Perot interferometer in conjunction with computerized data acquisition and analysis techniques, phase measurements with precisions of the order of X/100 can be made. With proper refractive index calibration, this precision results in a wall-thickness measurement accuracy of about 0.1%; and the density of the gas inside the microballoon is found with an accuracy of about 1% of its measured value.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mark D. Wittman, Daniel Malacara, and Hong-Jin Kong "High-precision characterization of gas-filled shells using scanning Fabry-Perot interferometry", Proc. SPIE 1553, Laser Interferometry IV: Computer-Aided Interferometry, (1 January 1992);

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