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LGS at the LBT-

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

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LGS at the LBT-

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  1. LGS at the LBT- A Road Map to GLAO and Upgrades Sebastian Rabien

  2. 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 But fringe tracker limited Z~2 dynamics Large samples needed GLAO GLAO DL Filippo Jets, stellar discs DL SN z~1 DL GRB DL AGN’s DL Optically faint galaxies GLAO High-z cases GLAO Mass-metallicity relation DL Merging history GLAO Roger: Thermal capabilities DL?

  3. Goals of a Laser Guide Star System at the LBT Phased approach • Provide as soon as possible moderate • correction with laser guiding over large field for: • Lucifer Spectroscopy • Lucifer Imaging 1st Step Enhance the observing efficiency and sensitivity 2nd Step • High Strehl on Axis • Large field high Strehl?

  4. System possibilities under discussion

  5. First estimations of system performance Cn2 profile from S. Egner 7 layers x fudge factor 2 h km

  6. 7 layers at: 0.5, 0.8, 2.5,5, 10, 15, 20 km Stars distributed over 300’’ field X 1 laser center Δ 3 lasers R=2‘ ם 5 lasers R=2‘ Without: fitting error, S/N from star, AO bandwidth ‘Sodium’ Low altitude guide stars can provide a good ground layer correction ‘Rayleigh’ 6km ‘Rayleigh’ 6km ‘worse seeing’

  7. Theses • 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 • 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.

  8. 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 Upgrade Road Provision: 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 • 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

  9. 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

  10. Modeling of system performance Comparison with science goals • 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

  11. Technology study Laser system and type Detail Launch concept WFS layout/ optics WFS Detector & Gating type (electronic shutter/EO-shutters) Calibration source Mechanical constrains/ layout Mechanical analysis (flexure, etc) Electronics needs (motorization, control loops, etc) Operational scenario/ installation scenario Observatory constrains, definition of requirements to LBT Computational needs Software needs Impact on observations (Installation, commissioning) Timescales for implementation Costing Manpower needs Availability of people Upgradeability Upgrades planning

  12. Laser issues Best candidates Pulsed green systems: Jdsu YAG • Available commercial • Good beam quality • Easy operation • 532nm Nd or 515nm Yb feasible ELS, disc

  13. 589nm lasers Dye lasers Proven technology 20W demonstrated Bulky Chemicals needed Maintenance intense Medium costs Nd-YAG sum frequency Proven technology 13 (50) W demonstrated Bulky Solid state Medium maintenance High costs Fiber lasers Less mature 5W demonstrated Very compact Solid state Low maintenance Low costs Currently no ‘easy’ option available

  14. 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

  15. 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 pixel 2 e- noise 256x256 pixel

  16. Cost and FTE expectations Example done for a multi Rayleigh system

  17. Timeline Technology Decision Preliminary design Today’s meeting Design review Test review Commissioning Phase A Concept comparison Performance calculation Technology evaluation Preliminary design Phase B Design Phase C Manufacturing Phase D Shipping Installation Phase A: 6 month Phase B: 1 year Phase C: 1 year Goal: Operation 2010

  18. A LGS facility is a must to keep LBT competitive A phased approach leads to an early implementation • GLAO first • High strehl next We have to start immediately

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