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LGS at the LBT-. A Road Map to GLAO and Upgrades. Sebastian Rabien. Science cases from this morning. Laird: Deep fields, faint targets The ‘20% seeing case’ Big field of view ‘Planets’, binarys Sky coverage at high strehl. Frank Highest angular res: Interferometry - PowerPoint PPT Presentation
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LGS at the LBT-
A Road Map to GLAO and Upgrades
Sebastian Rabien
Science cases from this morning
Laird:
Deep fields, faint targetsThe ‘20% seeing case’Big field of view
‘Planets’, binarysSky coverage at high strehl
Filippo
Jets, stellar discs DLSN z~1 DLGRB DLAGN’s DLOptically faint galaxies GLAOHigh-z cases GLAOMass-metallicity relation DLMerging history GLAO
Frank
Highest angular res: InterferometryBut fringe tracker limitedZ~2 dynamics Large samples needed
Roger:
Thermal capabilities DL?
DL
GLAOGLAO
Goals of a Laser Guide Star System at the LBT
Provide as soon as possible moderate correction with laser guiding over large field for:
•Lucifer Spectroscopy•Lucifer Imaging
•High Strehl on Axis•Large field high Strehl?
Enhance the observing efficiency and sensitivity
Phased approach
1st Step
2nd Step
System possibilities under discussion
SR-LGS MR-LGS S-LGS MS-LGS
Single Rayleigh LGS: gated at low altitude
Multiple Rayleigh stars
Single Sodium
Multiple Sodium
On-axis performance
Medium Medium High High
Homogenity Medium High Low High
Tech. Risk Optics/ Detectors
Optics/ Detectors
Laser Laser
Cn2 profile from S. Egner
x fudge factor 2
h km
7 layers
First estimations of system performance
X 1 laser centerΔ 3 lasers R=2‘
5 ם lasers R=2‘
‘Sodium’
‘Rayleigh’ 6km ‘Rayleigh’ 6km ‘worse seeing’
7 layers at: 0.5, 0.8, 2.5,5, 10, 15, 20 kmStars distributed over 300’’ field
Without: fitting error, S/N from star, AO bandwidth
Low altitude guide stars can provide a good ground layer correction
•Low altitude guide stars can provide a good ground layer correction•Multiple stars provide a more homogeneous PSF over the field•A single sodium provides high on-axis strehl
Theses
Further Studies needed for detailed decisions, like:
•How many stars?•Where best in the field?•Detection technology?•…
Should be answered in Phase A study
Constrains:
No easy sodium laser currently available.
Proposal for a staged approach
Start with multi Rayleigh low altitude gated system
•Provides homogeneous GLAO•Could be implemented fast•Mostly commercial components can be used•Leave the current NGS sensor in place•Can be used with co-adding and separate spot detection
Design the launch system to be suitable for general purpose
Leave space for additional (yellow) laser
Design of the high strehl (yellow? Cw, pulsed?) WFS to be foreseen in the system
Upgrade Road Provision:
•Provides the high strehl on axis correction•Leaves tomography option open•Single high altitude+ multiple low altitude stars could be a nice path towards MCAO
Phase A study includes:
Modelling of system performance:
•N-Rayleigh guide stars at x-altitude•Compare with Sodium option
Develop roadmap of upgrades
Technology study
Preliminary design
Phase A Performance Study of LGS Systems:
•Single low altitude guide star•Multiple low altitude stars•Single high altitude•Multiple high altitude stars•Modeling of S/N for laser type•Modeling of fitting and bandwidth
Including: good/medium/bad conditions
Modeling of system performanceComparison with science goals
Technology study
Laser system and typeDetail Launch conceptWFS layout/ opticsWFS Detector & Gating type (electronic shutter/EO-shutters)Calibration source
Mechanical constrains/ layoutMechanical analysis (flexure, etc)Electronics needs (motorization, control loops, etc)
Operational scenario/ installation scenarioObservatory constrains, definition of requirements to LBT
Computational needsSoftware needs
Impact on observations (Installation, commissioning)
Timescales for implementationCostingManpower needsAvailability of peopleUpgradeability
Upgrades planning
Laser issues
Pulsed green systems:
•Available commercial•Good beam quality•Easy operation•532nm Nd or 515nm Yb feasible
ELS, disc
Jdsu YAG
Best candidates
Nd-YAG sum frequency
Proven technology13 (50) W demonstratedBulkySolid stateMedium maintenanceHigh costs
Fiber lasers
Less mature5W demonstratedVery compactSolid stateLow maintenanceLow costs
Dye lasers
Proven technology20W demonstratedBulkyChemicals neededMaintenance intenseMedium costs
Currently no ‘easy’ option available
589nm lasers
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
WFS remarks and questions
Low altitude detection system is not straightforward•Space constrains•Large backfocal distance
New or separate dicroic needed?
Detectors
Single detector preferable (cost)Optically switching preferred (best CCD can be used)Leaves upgrade to cw/ sodium detection
50μm pixel2 e- noise256x256 pixel
Cost and FTE expectationsKomponents Hardware Costs
Laser Sum 1300 k€
Electronics and Computers 100 k€
Lasers 800 k€
Optics und Mechanics 400 k€
Else 100 k€
Projektion Sum 1300 k€
Electronics and computers 200 k€
Beam transport 300 k€
Teleskopes 500 k€
Aircraft avoidance 100 k€
else 100 k€
Wellenfrontsensor Sum 800 k€
Computers and electronics 200 k€
Detectors and electronics 300 k€
Optics and mechanics 200 k€
else 100 k€
Installation Sum 300 k€
Change to telescope, infrastructure
100 k€
Transport / Travel 100 k€
Installation at telescope 100 k€
Continguency (10%) Sum 400 k€
Total 4100 k€
Aufgabe FTE‘s
Management 2
System Engineering 4
Construction 4
Elektronics 4
Software 4
Mechanical workshop 6
Electronics workshop 2
Integration and Test 8
Continguency (10%) 4
Sum 38
With 50 k€ / Personenjahr
= 1900 k€
Example done for a multi Rayleigh system
Timeline
Today’s meeting
TechnologyDecisionPreliminary design Design review Test review Commissioning
Phase A
Concept comparisonPerformance calculationTechnology evaluationPreliminary design
Phase B
Design
Phase C
Manufacturing
Phase D
ShippingInstallation
Goal: Operation 2010Phase A: 6 monthPhase B: 1 yearPhase C: 1 year
We have to start immediately
A LGS facility is a must to keep LBT competitive
A phased approach leads to an early implementation
•GLAO first•High strehl next