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Progress in understanding flatness measurements

Progress in understanding flatness measurements. Tom Diehl November 24, 2005. Draft as of 11/24/05. Micro-Epsilon Opto-NCDT 2400. We need to control the flatness of the focal plane. We need to measure components without touching their surfaces.

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Progress in understanding flatness measurements

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  1. Progress in understanding flatness measurements Tom Diehl November 24, 2005 Draft as of 11/24/05

  2. Micro-Epsilon Opto-NCDT 2400 • We need to control the flatness of the focal plane. • We need to measure components without touching their surfaces. • Using a DEMO version Jim Fast determined that this device could measure the distance to the surface of a CCD mounted in the test dewar through the dewar’s quartz window. • 100 micron spot diameter • 24 mm measurement range at 222 mm distance • ~1 micron resolution

  3. Digital Output To Labview Controls DSP Power Supply Polychromatic Light Source Spectrometer Sensor On X-Y Stager CCD Fiber Optic Cable l2 l1 Micro-Epsilon Opto-NCDT 2400

  4. The Machinery • Labview controls X and Y dimension Stages w/ ~1 micron precision On the scale of our devices Micro-epsilon imager Sample

  5. Silicon on a pedestal • Example of a ¼ mm x ¼ mm scan of a part with very reflective surface. Non-flat surface features are evident.

  6. Silicon Piece 6 cm x 3 cm • Glued to aluminum nitride substrate • Taped to a piece of unistrut. The device overlaps the unistrut by ~ 1 cm on each side. • Surface has observable grind marks from a thinning process.

  7. 2 Imagesof Same Device • ½ mm x ½ mm grid • Offset by 0.1 mm in • Y direction illustrates the • problem. • One can see the warp in • the surface but only that • general feature matches. • Individual points do not.

  8. Systematic Uncertainty • The measurements of a point on the surface hold within about 1 micron. • If I move off and move back on the measurement repeats. • If I move by off by 1/10 mm, the measurement is more different than what I think is the height of the typical surface feature. Spurious reflections from the grind marks trick the system? • A systematic unc’y is determined from 2 measurements offset by 1/10 mm. • deltaZ=delta(Za-Zb)/sqrt(2)~15 microns

  9. “Greg’s Device” 6 cm x 3 cm • Average the measurements in ½ cm x ½ cm array. The total uncertainty on mean in each of the 72 regions is ~ 1 micron. 13/72 regions <z> gt 10 microns

  10. The Plan • A few more improvements to the Labview program • Automation is pretty good. • Surface feature identification and concentration is nearly done • Bring into the CCD testing Lab • operate through a window • Incorporate results into the DES CCD database • Develop a flatness grade for each CCD • Develop a way to test the DES Focal plane assembly

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