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FISS Fast Imaging Solar Spectrograph for NST New Solar Telescope at Big Bear

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FISS Fast Imaging Solar Spectrograph for NST New Solar Telescope at Big Bear

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    1. FISS (Fast Imaging Solar Spectrograph) for NST (New Solar Telescope) at Big Bear

    2. Contents

    3. Introduction New Solar Telescope at Big Bear Solar Observatory (NJIT) 1.6 m off-axis telescope with f-ratio 52 High-order adaptive optics Stable solar images with diffraction-limited resolution : 0.07” at 500 nm and 0.15” at 1000 nm

    4. Introduction Optical Layout of NST

    5. Introduction New Solar Telescope at Big Bear Solar Observatory Two major scientific Instruments : Visible light imaging vector magnetograph (VIM) : Infrared imaging vector magnetograph (IRIM) <= based on Fabry-Perot filters <= ideal for photospheric lines which are narrow and shifted only by a small amount : However, they are not suited for chromospheric lines such as Ha and He I lines which may be either very broad or may be highly shifted. Instrument for the study of chromospheric phenomena => Fast Imaging Solar Spectrograph (FISS) : Chromospheric features - Filaments/ prominences - Flares - Jet-like features ( spicules, mottles, surges, upflow events, and so on )

    6. FISS for Filament Threads High spatial resolution < 0.2” High spectral resolution & mlti-line covergae High temporal resolution

    7. Concept & Data requirement of the FISS Basic design concept of the FISS Full-reflecting Echelle spectrograph of Littrow type Recording two spectral bands at Ha and Ca II IR simultaneously Fast imaging based on fast scan and fast CCD Cameras :It operates either in spectrograph mode or in imaging mode with fast scan at the sacrifice of spectral resolution.

    8. Concept & Data requirement of the FISS Basic Design Parameters of FISS

    9. Optical Design and Tolerance Analysis of the FISS Optical Design of FISS

    10. Optical Design and Tolerance Analysis of the FISS Optical Performance of FISS

    11. Optical Design and Tolerance Analysis of the FISS Tolerance Analysis of FISS Tolerance analysis process <= iterative process Specifying the tolerance : fabrication & align errors Sensitivity analysis Estimating overall performance Tolerance Error Range for Sensitivity Analysis

    12. Optical Design and Tolerance Analysis of the FISS Sensitivity Analysis : Performance criterion - image RMS spot size (mm)

    13. Optical Design and Tolerance Analysis of the FISS Inverse Sensitivity Analysis

    14. Optical Design and Tolerance Analysis of the FISS Sensitivity Analysis : Performance criterion - image RMS spot size :Compensator : thickness surf 21

    15. Slit spectroscopy

    16. Scanning tip-tilt mirror At the pupil, all the chief rays coincide. Regardless of scanner’s tilt, chief rays are located at the same point on the mirror. A field scan of 0.1” corresponds to a mirror tilt of 1/1000°(3.6”).

    17. Scanner in absence of a pupil NST will include adaptive optics; this does not guarantee the existence of a pupil. NST may give a collimated beam. Two solutions Add some lenses to make a pupil ?inefficient Develop a pupilless scanner

    18. The MISC (the Micro-Image-Scanner) This is a mirror version of a dove prism. When the mirror set moves at a distance of ?x, rays move at a distance of 2?x. Images will be inverted up and down. In this design, a movement of 9.3µm(approximately 10µm) corresponds to a field change of 0.1”. This configuration is complex Uses 3 mirrors Large scan field requires bigger mirrors.

    19. Two-mirror scanner Pros : 2 mirrors – smaller than 3. Cons : Rays must be changed; change in direction or in position.

    20. Gerenalized 2-mirror scanner Pros : The angle between incident beam and outward beam is variable( 0~180° ). a scanner movement of ?x makes a field shift of Small ? makes ?(field)/?x small - precise scan is possible, while it requires longer mirror size. Example) When GH=24mm and ?=22.5°, DF=32.9mm Minimum mirror size = DF + RH + RD

    21. Motion control - procedure

    22. Motion control - motor Tip-tilt : Piezoelectric tip-tilt unit Two-mirrored : linear motor Rotational motor with worm gear Inaccurate, friction, wearing down, dust. Linear motor Accurate(nm scale), no friction, repeatability, long life To select appropriate linear motor, motor type( cored or coreless ), mover weight, positioning resolution, maximum velocity and stroke should be carefully considered.

    23. Expected scanning performance For ?=22.5°(Beam reflects by 90°.) case, all length-related values are multiplied by sqrt(2).

    24. Future Works

    26. Tip-tilt mirror scanner

    27. Problems of different incident angle Each field goes to different mirror position. As the mirror tilts, chief ray angle of entering beam differs. Therefore, a field change makes different incident angle. ( 0.48° for 43” field difference )? 32.5A shift(12mm) at the CCD

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