Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2x lO 9 has been measured at T=3.5K.We have been studying large dielectric and semiconductor single crystals as possible gravitational wave detectors. 1 These detectors are frequently cylinders instrumented to detect vibrations of the first longitudinal mode. One of the important desirable properties is a high mechanical quality factor Q. With an ideal transducer the sensitivity to gravitational waves is proportional to Q. The inverse quality factor Q-1 is a direct measure of the dominant mechanism of the attenuation of first sound. Measurements of Q are frequently the best way to gather information concerning the various internal loss mechanisms of a substance. In the region of very high Q (low loss) this sometimes is the only easy method. We report here on measurements on a large single crystal of silicon whose Q values exceed 10 9.The crystal was manufactured by Monsanto by the zero-dislocation Czochralski process in the form of a cylinder (diameter 10.6 cm, length 22.9 cm, mass 4.9 kg), with the [111] axis parallel to the cylinder axis. The ends were polished by the University of Rochester Institute of Optics personnel to better than one wavelength of light. The barrel of the crystal, somewhat wavy from the crystal growing process, was left in this state so that its edge deviates from straightness by -1 mm. The crystal is a p-type

National Ignition Facility (NIF) is a high-energy laser facility comprised of 192 laser beams focused with enough power and precision on a hydrogen-filled spherical, cryogenic target to initiate a fusion reaction. The target container, or hohlraum, must be accurately aligned to an x-ray imaging system to allow careful monitoring of the frozen fuel layer in the target. To achieve alignment, x-ray images are acquired through starburst-shaped windows cut into opposite sides of the hohlraum. When the hohlraum is in alignment, the starburst pattern pairs match nearly exactly and allow a clear view of the ice layer formation on the edge of the target capsule. During the alignment process, x-ray image analysis is applied to determine the direction and magnitude of adjustment required. X-ray detector and source are moved in concert during the alignment process. The automated pointing alignment system described here is both accurate and efficient. In this paper, we describe the control and associated image processing that enables automation of the starburst pointing alignment.

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