Laser Launch System for the LBT
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Laser Launch System for the Laser Launch System for the LBTLBT
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”
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Launch Systems in UseLaunch Systems in Use
Mt Wilson 100”
pulsed Rayleigh laser;launched from Primary mirror;focussed at 18km
need to sharing telescope optical system (block optical path while laser fires);control alignment of laser on optical axis
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).
sketch of beam path directing the beam onto the coude axis
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Launch Systems in UseLaunch Systems in Use
Keck, Lick, ALFA, SOR
master laser on dome floor & amplifier on M1 cell: dye tubes & fibre in cable wrap;side launch: simple beam relay but elongated spots;
launch lens at top of beam tube
LGS spots on Keck WFS
Sketch of Keck Telescope
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Launch Systems in UseLaunch Systems in Use
VLT, Subaru
laser on Nasmyth platform (constant gravity vector);photonic crystal fibre as relay (only possible for cw lasers);central launch telescope
Subaru fibre
Subaru launch telescope (small secondary)
Sketch of Subaru Telescope
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Launch Systems in UseLaunch Systems in Use
Gemini North (& South), Palomar 200”, MMT
laser at M1 cell;actively controlled mirror relay;central launch telescope
Gemini North beam relay
Gemini North
5mm beam fits behind narrow support fin
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Launch Systems in UseLaunch Systems in Use
WHT
laser mounted on top ring leads to minimalist beam relay;central launch telescope
single laser for GLAO
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Launching Multiple Laser BeamsLaunching Multiple Laser Beams
VLT (for HAWK-I & MUSE)4 launch telescope around M1 cellneeded for cw lasers to avoid fratricide
MMT1 central launch telescope;split beam holographically;for pulsed lasers, gating avoids fratricide
Gemini South1 central launch telescope;multiple beams directed into LT; pointings can be controlled independently
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Laser Launch Telescope for Gemini Laser Launch Telescope for Gemini South 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
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Laser Launch Telescope for VLTLaser 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;
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• on-axis design with 46 cm diameter, F/1.8 primary
• Installed behind secondary
• LT Transmission 87%
• open structure
Laser Launch Telescope for Palomar Laser Launch Telescope for Palomar 200” 200”
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Basic Design ConsiderationsBasic 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
launchinglaunch 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)
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Distributed Launch Telescopes not Distributed Launch Telescopes not possiblepossible
space around M1 cell blocked by M3 arm
space around M1 cell blocked by walkway
View of LBT M1 mirror cell
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Laser mounted on platform above Laser mounted on platform above LuciferLucifer
Two 1m electronics cabinets
laser heads
diagnostics & alignment optics
platform removable in 2 halves
identical installation here
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Access to LUCIFER auxiliary cryostatsAccess to LUCIFER auxiliary cryostats
LUCIFER auxiliary cryostats
laser platform
laser platform
Top View between mirror cells
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laser platform
LUCIFER main cryostatsTop View between mirror cells
Access to LUCIFER main cryostatsAccess to LUCIFER main cryostats
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Launch Telescope mounted behind M2Launch Telescope mounted behind M2
narrow (~10cm) beam relay
launch telescope & beam expander
laser platform
non-rigid connection
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Central launch, with expander built into beam relay Central launch, with expander built into beam relay
flat folding mirror launches beam upwards
laser platform
open air propagation from here
beam expanded by lenses in wide (~45cm) relay
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Attachment of beam relay cover tubesAttachment of beam relay cover tubes
Pads already available on telescope structure
Beam relay cover
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Things to think about when launching laser Things to think about when launching laser beamsbeams
aircraft avoidance systemrequirements from FAA & Space Commandhuman spottersall-sky cameraradar information from airportsbore-sight camera (infrared/optical)
interlockstemptation is to make these too complex
laser traffic control systemprocure tool used at Mauna Kea & Cerro Pachon?own development?
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Proposed Design for the LBT LGSFProposed Design for the LBT LGSF
beam expanded by lenses in wide (~45cm) relay
flat folding mirror launches beam upwards
open air propagation from here
laser platform