An experimental investigation has been made on plasma closure in pinholes irradiated by Nd glass laser pulses; 300–500-μm diam pinholes of various materials and thicknesses have been irradiated by 20–100-J 300-psec FWHM pulses on the Janus laser system. Calorimetry measurements have yielded data on pinhole energy transmission and intensity loading on the periphery of the pinhole. Ultrafast streak photography measurements indicate effective closure velocities of 2–5 × 107 cm/sec. Scattered light measurements have shown the transmission loss through a typical spatial filter configuration to be primarily refractive in nature.
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