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Laser Launch System for the LBT

Laser Launch System for the LBT. Richard Davies Sebastian Rabien Max Planck Institute for Extraterrestrial Physics. Approaches of other observatories Trade-offs that should be considered Possibilities for LBT.

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Laser Launch System for the LBT

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  1. Laser Launch System for the LBT Richard Davies Sebastian Rabien Max Planck Institute for Extraterrestrial Physics • Approaches of other observatories • Trade-offs that should be considered • Possibilities for LBT SOR, Calar Alto, Lick, MMT, Keck, VLT, Subaru, Gemini North, WHT, Palomar 200”, Mt Wilson 100”

  2. Launch Systems in Use Mt Wilson 100” sketch of beam path directing the beam onto the coude axis need to sharing telescope optical system (block optical path while laser fires); control alignment of laser on optical axis pulsed Rayleigh laser; launched from Primary mirror; focussed at 18km not an option for ‘classical’ LGS on 8-m telescope; but would be used for some novel techniques such as laser phase shifting interferometry (Rabien et al. 2006).

  3. Launch Systems in Use Sketch of Keck Telescope Keck, Lick, ALFA, SOR launch lens at top of beam tube master laser on dome floor & amplifier on M1 cell: dye tubes & fibre in cable wrap; side launch: simple beam relay but elongated spots; LGS spots on Keck WFS

  4. Launch Systems in Use VLT, Subaru Sketch of Subaru Telescope Subaru fibre laser on Nasmyth platform (constant gravity vector); photonic crystal fibre as relay (only possible for cw lasers); central launch telescope Subaru launch telescope (small secondary)

  5. Launch Systems in Use Gemini North Gemini North (& South), Palomar 200”, MMT Gemini North beam relay 5mm beam fits behind narrow support fin laser at M1 cell; actively controlled mirror relay; central launch telescope

  6. Launch Systems in Use WHT single laser for GLAO laser mounted on top ring leads to minimalist beam relay; central launch telescope

  7. Launching Multiple Laser Beams VLT (for HAWK-I & MUSE) 4 launch telescope around M1 cell needed for cw lasers to avoid fratricide MMT 1 central launch telescope; split beam holographically; for pulsed lasers, gating avoids fratricide Gemini South 1 central launch telescope; multiple beams directed into LT; pointings can be controlled independently

  8. Laser Launch Telescope for Gemini South • afocal 60:1 expander, projecting 45cm collimated beam to sky • installed behind secondary • off-axis parabola design • designed to launch 5 beams of 10W each • care needed for glass & coating resistance to laser power density 500-1000W/cm2 • aluminium construction with carbon fibre thermal rod to maintain distance from expander to primary mirror

  9. Laser Launch Telescope for VLT • afocal 12.5:1 expander (36cm beam size) with 50cm primary mirror • on-axis with small secondary • diagnostics in situ (but not used) • suitable for launching multiple beams • ~F/1 (due to space restrictions), so thermally sensitive • enclosed structure filled with N2; totally surrounded by wind baffle;

  10. Laser Launch Telescope for Palomar 200” • on-axis design with 46 cm diameter, F/1.8 primary • Installed behind secondary • LT Transmission 87% • open structure

  11. Basic Design Considerations fibre – not compatible with pulsed lasers. (e.g. VLT) alignment into small fibre can be problematic throughput an issue for high power, long fibres, and small bending radii. mirrors - complex if many must be servoed. (e.g. Gemini) in a static relay, only flexure need be compensated. throughput good for short relays with few optics. lenses - long focal length expander is part of beam relay. (e.g. Keck) scattered light may be an issue if beam is centrally launched beam relay launching launch telescope(s) distributed (top ring? space around M1 cell?) central (headroom? weight limit?) on axis or off axis beam expander? (e.g. VLT) (e.g. Gemini) (light loss, manufacturing, alignment)

  12. Distributed Launch Telescopes not possible View of LBT M1 mirror cell space around M1 cell blocked by M3 arm space around M1 cell blocked by walkway

  13. Laser mounted on platform above Lucifer diagnostics & alignment optics Two 1m electronics cabinets laser heads platform removable in 2 halves identical installation here

  14. Access to LUCIFER auxiliary cryostats Top View between mirror cells LUCIFER auxiliary cryostats laser platform laser platform

  15. Access to LUCIFER main cryostats Top View between mirror cells LUCIFER main cryostats laser platform

  16. Launch Telescope mounted behind M2 non-rigid connection launch telescope & beam expander narrow (~10cm) beam relay laser platform

  17. Central launch, with expander built into beam relay open air propagation from here flat folding mirror launches beam upwards beam expanded by lenses in wide (~45cm) relay laser platform

  18. Attachment of beam relay cover tubes Pads already available on telescope structure Beam relay cover

  19. Things to think about when launching laser beams aircraft avoidance system requirements from FAA & Space Command human spotters all-sky camera radar information from airports bore-sight camera (infrared/optical) interlocks temptation is to make these too complex laser traffic control system procure tool used at Mauna Kea & Cerro Pachon? own development?

  20. Proposed Design for the LBT LGSF open air propagation from here flat folding mirror launches beam upwards beam expanded by lenses in wide (~45cm) relay laser platform

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