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Vacuum support for LSST secondary measurement - Midterm presentation -

Vacuum support for LSST secondary measurement - Midterm presentation -. Masaki Hosoda 4/8/2010 523L Individual Project. Contents. Background Purpose Plan for project Experimental Setup. Background.

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Vacuum support for LSST secondary measurement - Midterm presentation -

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  1. Vacuum support for LSST secondary measurement - Midterm presentation - Masaki Hosoda 4/8/2010 523L Individual Project

  2. Contents • Background • Purpose • Plan for project • Experimental Setup

  3. Background Prof. Dubin et al. tries to measure the Large Synoptic Survey Telescope (LSST) secondary mirror by Fizeau type interferometer with 5mm gap as shown in Figure [1]. In this case, the bending of the test plate caused by the gravity becomes a problem, since the test plate is flipped around after polishing the reference surface. Reducing an unexpected bending in the reference surface is significant. [1] M. B. Dubin, et al., “Fizeau interferometer with spherical reference and CGH correction for measuring large convex aspheres”, Proceedings of the SPIE, Volume 7426 (2009)

  4. Purpose • The purpose of this individual project is to do a simple experiment showing correspondence between simulation and experiment.

  5. Plan for project • Step 1. Hand calculation on LSST model (Done) • Check a surface deflection of Test Plate caused by gravity • Check a surface deflection of Test Plate caused by vacuum • Summarize an effectiveness of vacuum technique • Step 2. Simulation on a simple model • Design a simple model (100mm in diameter, 2.69mm in thickness) • List the Zernike terms depending on pressure [Pa] • Step 3. Experiment on a simple model • Set up the vacuum equipment, lenses, and sealing material • Measure the Zernike terms depending on pressure [Pa] • Show simulation works based on the comparison of simulation data with experimental data • Step 4. Simulation to LSST model (in 523 class) • Simulate wavefront caused by gravity (Solidworks -> Zemax) • Simulate wavefront caused by vacuum (Solidworks -> Zemax) • Show how much uncertainty caused by gravity can be reduced by using vacuum technique

  6. Hand calculations • vacuum deflects the lens as the following. In this case, CD = 0.943 (Continuous support along diameter) by Vukobratovich page 261. Since Pressure (P) = Force / Area = ρgh, then, • About 1000 [Pa] (0.15 [psi]) is needed for a simple experiment.

  7. Experimental Setup Flat Surfaces Needle Scale O-ring Leak Valve Vacuum Pump Reservoir Water Pressure Gage

  8. Pictures (Lenses)

  9. Pictures (Pump and Valve)

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