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Sodium monitoring experiment in Chile

Sodium monitoring experiment in Chile. Céline d’Orgeville. Presentation overview. Sodium physics Mesospheric sodium facts Laser-sodium interaction basics Sodium monitoring experiment at CTIO Experimental set-up Pretty pictures  Preliminary results. Mesospheric sodium characteristics.

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Sodium monitoring experiment in Chile

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  1. Sodium monitoring experiment in Chile Céline d’Orgeville

  2. Presentation overview • Sodium physics • Mesospheric sodium facts • Laser-sodium interaction basics • Sodium monitoring experiment at CTIO • Experimental set-up • Pretty pictures  • Preliminary results MCAO Preliminary Design Review

  3. Mesospheric sodium characteristics Annual mean = 4.3 109 atoms/cm2 6 Na abundance (109atoms/cm2) 4 2 Months Sodium monitoring at Urbana, Illinois • Origin: meteoritic • Mean altitude: 90-95km • Thickness: 5-12km • Column density: 1-10 109 atoms/cm2 • Yearly, nightly and hourly variations of sodium abundance, altitude and layer thickness • Latitude dependence • Sporadic events MCAO Preliminary Design Review

  4. Importance of sodium parameters for AO • Sodium abundance • LGS photon return proportional (no saturation) or almost proportional (small saturation case) to sodium column density  Fix laser power requirement • Yearly and nightly variations • Seasons more favorable for LGS AO observations • Queue scheduling • Layer altitude • AO focus correction can be mislead by • Fast altitude variations • Sporadic events MCAO Preliminary Design Review

  5. Importance of sodium parameters for AO • Sodium monitoring experiment in Chile • Funding • Gemini, CTIO/NOAO & ESO • CTIO telescope time proposals • PI – Celine d’Orgeville • Co-PI’s • Imperial College: Chris Dainty • Gemini: Mark Chun • CTIO: Brooke Gregory, Andrei Tokovinin, Maxime Boccas • Coordination with local air traffic control • Enrique Figueroa MCAO Preliminary Design Review

  6. Sodium monitoring experiment • Use Imperial College experimental set-up (sodium monitoring in La Palma, Canaries Islands, 1999-2000) • Low power laser • Launch telescope • Planning 5 runs over a year • Feb., May, Sept., Nov/Dec. 2001 and Feb. 2002 • Bright time • 0.9m and Schmidt telescopes • First run: Feb 11-20  10 nights worth of data • Second run: May 2-11  3 nights of data out of 10 nights allocated MCAO Preliminary Design Review

  7. Sodium monitoring with a laser – just another laser guide star MCAO Preliminary Design Review

  8. Sodium atoms / laser light interaction physics D2 line: l=589.0 nm 32P3/2 3P 32P1/2 F=2  F=3 3S 32S1/2 MCAO Preliminary Design Review

  9. Sodium atoms / laser light interaction physics X 6 10 Inefficient spectral format (bandwidth > 3 GHz) 14 18 Maximum efficiency at the 10-W level X Max. efficiency zone Photon returnper Watt ofCW laser power Laser bandwidth (MHz) Saturation X Laser power (W) • Interaction efficiency depends on: • Laser temporal format (CW or pulsed) • Laser spectral format (compared to Na D2 line) • Laser peak intensity (saturation) • E.g. simulation for CW laser MCAO Preliminary Design Review

  10. Experimental set-up e ~ 10 km 0.9 m Schmidt q ~d e / h2 ~ 35 arcsec h ~ 90 km LASER CTIO 0.9m / Schmidt d0.9 ~ 140 m dSchm ~ 110 m MCAO Preliminary Design Review

  11. Optical bench: laser + launch tower MCAO Preliminary Design Review

  12. Aligning the laser… MCAO Preliminary Design Review

  13. Hole in the roof ! MCAO Preliminary Design Review

  14. Laser beam !!! MCAO Preliminary Design Review

  15. Experimental resolution • Spatial resolution • Ultimately set by 0.9m telescope CCD pixel size = 0.4 arcsec  Dh ~ 115 m • But during the first run we observed LGS width as large as 3-6 arcsec (increasing during the night)Dh ~ 0.8-1.7 km • Cerro Tololo seeing • 0.9m defocus • 0.9m dome seeing • Seeing induced by heat exchange between laser room and outside air Sealed hole in the roof with plastic sheet attached to LLT • Second run: 2-4 arcsec LGS width Dh ~ 0.5-1.1 km MCAO Preliminary Design Review

  16. Experimental resolution 120 LGS width = 3" bin = 2 100 80 60 SNR 40 20 40 60 20 Time (s) • Temporal resolution • We took 10-60s exposures depending on atmosphere transparency (>10s when clouds) • For LGS magnitude = 14.5 and width = 3 arcsec, simulation predicts: • DT ~ 10 s for SNR ~ 40 where signal is the sum of binned pixel signal over LGS width MCAO Preliminary Design Review

  17. Preliminary results Sodium guide star (~ 90 km) Rayleigh scattering (< 30 km) MCAO Preliminary Design Review

  18. Preliminary results February 18, 2001 22:35-23:50 MCAO Preliminary Design Review

  19. Feb 11, 2001 Feb 12, 2001 Feb 13, 2001 Feb 14, 2001 Feb 15, 2001 Feb 16, 2001 MCAO Preliminary Design Review

  20. Data reduction…on-going • Full data-reduction includes: • Star calibration  telescope throughput + atmospheric transmission • Laser power calibration • Triangulation method • Derive profile parameters (column density, altitude) • Compare with data obtained at ESO Paranal and La Silla • Statistics • Update laser power requirements and MCAO performance MCAO Preliminary Design Review

  21. Friday, 5/25 0800 Laser System 0900 CTIO Sodium Studies 0915 Control System 0945 Break 1000 RTC Electronics 1045 Safety System 1100 Availability analysis 1130 Closed vendor Sessions 1200 Lunch 1300 Cost and schedule 1400 Committee session 1700 Committee report 1800 Adjourn PDR Agenda MCAO Preliminary Design Review

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