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The LiCAS Straightness Monitor

The LiCAS Straightness Monitor. Straightness Monitors. Ideas behind the LiCAS straightness monitor system System components and design Data Processing and Analysis. y. z. How does it work?. Used to measure carriage transverse translations and rotations

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The LiCAS Straightness Monitor

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  1. The LiCAS Straightness Monitor DESY Gathering

  2. Straightness Monitors • Ideas behind the LiCAS straightness monitor system • System components and design • Data Processing and Analysis DESY Gathering

  3. y z How does it work? • Used to measure carriage transverse translations and rotations • Require 1μm precision over length of train Rotation: Spots move opposite directions Translation: Spots move same direction CCD Camera DESY Gathering

  4. y y z x Rotations about Z • Use two parallel beams to measure rotation about z-axis SM beams coming out of the screen Image of beam spots observed on CCD Camera DESY Gathering

  5. Straightness Monitors • Ideas behind the LiCAS straightness monitor system • System components and design • Data Processing and Analysis DESY Gathering

  6. System Decisions • Beam Source • SLD, VCSEL, Low Coherence Laser • Beamsplitter Configuration • System Dimensions • Camera size • Reduction Optics DESY Gathering

  7. Low Coherence Beams • Low coherence length diode lasers are used to avoid CCD interference • Stray reflections off surfaces can interfere if coherent The two reflected rays can interfere if coherent The two reflected rays can interfere if coherent Beam- Splitters CCD Chip CCD Glass Face-plate DESY Gathering

  8. Laser with long coherence length. Interference rings observed on CCD Laser with low coherence length No interference structure is observed Perfect Gaussian Beam Interference Rings Interference Rings DESY Gathering

  9. CCD 1 CCD 2 y y z z Splitter Configurations • Single Beam Splitter + End carriage retro-reflector • Double Beam Splitter per carriage • Pro: Measurements independent of splitter angle • Con: Retro-reflector introduces unknown transverse walk to all carriages • Pro: No retro-reflector: No unknown walks • Con: The angle of each beam-splitter in each has to be determined; 12 extra calibration constants DESY Gathering

  10. Demagnification Lenses • CCD cameras are 0.27 cm2 (6.6mm x 4.1mm) • Collimated beam has large initial width • Possibly larger than the CCD • Use of demagnification lenses increase dynamic range • Lenses must be high quality to prevent beam distortion Lens CCD DESY Gathering

  11. Straightness Monitors • Ideas behind the LiCAS straightness monitor system • System components and design • Data Processing and Analysis DESY Gathering

  12. LabView Analysis DESY Gathering

  13. Stability Results ≈ 1mm ≈0.88mm DESY Gathering

  14. Translation Stage Results DESY Gathering

  15. Translation Stage Results DESY Gathering

  16. Rotation Stage Results DESY Gathering

  17. Rotation Stage Results DESY Gathering

  18. Past • Initial design of LiCAS Straightness Monitor completed • Analysis software written • Desired accuracy achieved with stationary components • Experimental system is motion ready • Desired accuracy to be achieved with motion • Decisions will be made for remaining configuration • Beamsplitter, Reduction Optics, Camera Size • Experimental range to be extended • Second camera to be added and Future DESY Gathering

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