Sodium monitoring experiment in Chile Céline d’Orgeville

MCAO May 24-25, 2001 MCAO Preliminary Design Review 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 May 24-25, 2001 Why laser guide stars ? Adaptive OpticsAdaptive Optics need a bright reference source but science objects are usually too faint NGSUse of a bright star nearby whenever possible (NGS) LGS laserIf not, create an ‘Artificial’’ Guide Star (LGS) with a laser

MCAO May 24-25, 2001 MCAO Preliminary Design Review 4 Mesospheric sodium characteristics Origin: meteoritic Mean altitude: 90-95km Thickness: 5-12km Column density: atoms/cm 2 Yearly, nightly and hourly variations of sodium abundance, altitude and layer thickness Latitude dependence Sporadic events Months Na abundance (10 9 atoms/cm 2 ) Annual mean = atoms/cm Sodium monitoring at Urbana, Illinois

MCAO May 24-25, 2001 MCAO Preliminary Design Review 5 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 May 24-25, 2001 MCAO Preliminary Design Review 6 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 May 24-25, 2001 MCAO Preliminary Design Review 7 Sodium monitoring experiment –Use Imperial College experimental set-up (sodium monitoring in La Palma, Canaries Islands, ) Low power laser Launch telescope –Planning 5 runs over a year –Feb., May, Sept., Nov/Dec and Feb –Bright time –0.9m and Schmidt telescopes First run: Feb  10 nights worth of data Second run: May 2-11  3 nights of data out of 10 nights allocated

MCAO May 24-25, 2001 MCAO Preliminary Design Review 8 Sodium monitoring with a laser – just another laser guide star

MCAO May 24-25, 2001 MCAO Preliminary Design Review 9 Sodium atoms / laser light interaction physics F=2  F=3 D2 line:  =589.0 nm 3P 3S 3 2 S 1/2 3 2 P 3/2 3 2 P 1/2

MCAO May 24-25, 2001 MCAO Preliminary Design Review 10 Sodium atoms / laser light interaction physics 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 Laser power (W) Laser bandwidth (MHz) X Inefficient spectral format (bandwidth > 3 GHz) Max. efficiency zone Maximum efficiency at the 10-W level X X Saturation Photon return per Watt of CW laser power

MCAO May 24-25, 2001 MCAO Preliminary Design Review 11 Experimental set-up e ~ 10 km h ~ 90 km d 0.9 ~ 140 m d Schm ~ 110 m  ~  d e / h 2 ~ 35 arcsec CTIO 0.9m / Schmidt 0.9 m Schmidt LASER

MCAO May 24-25, 2001 MCAO Preliminary Design Review 12 CTIO 0.9m telescope

MCAO May 24-25, 2001 MCAO Preliminary Design Review 13 Laser bench

MCAO May 24-25, 2001 MCAO Preliminary Design Review 14 Optical bench: laser + launch tower

MCAO May 24-25, 2001 MCAO Preliminary Design Review 15 Aligning the laser…

MCAO May 24-25, 2001 MCAO Preliminary Design Review 16 Hole in the roof !

MCAO May 24-25, 2001 MCAO Preliminary Design Review 17 Laser beam !!!

MCAO May 24-25, 2001 MCAO Preliminary Design Review 18 Hard workers in the cold of the night !!!!!

MCAO May 24-25, 2001 MCAO Preliminary Design Review 19 Experimental resolution Spatial resolution –Ultimately set by 0.9m telescope CCD pixel size = 0.4 arcsec   h ~ 115 m –But during the first run we observed LGS width as large as 3-6 arcsec (increasing during the night)   h ~ 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   h ~ km

MCAO May 24-25, 2001 MCAO Preliminary Design Review 20 Experimental resolution 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:   T ~ 10 s for SNR ~ 40 where signal is the sum of binned pixel signal over LGS width Time (s) SNR LGS width = 3" bin = 2

MCAO May 24-25, 2001 MCAO Preliminary Design Review 21 Experimental resolution 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:   T ~ 10 s for SNR ~ 40 where signal is the sum of binned pixel signal over LGS width SNR Time (s) 1 arcsec 3 arcsec 6 arcsec LGS mag = 13.7

MCAO May 24-25, 2001 MCAO Preliminary Design Review 22 Preliminary results Rayleigh scattering (< 30 km) Sodium guide star (~ 90 km)

MCAO May 24-25, 2001 MCAO Preliminary Design Review 23 Preliminary results

MCAO May 24-25, 2001 MCAO Preliminary Design Review 24 Preliminary results February 18, :35-23:50

MCAO May 24-25, 2001 MCAO Preliminary Design Review 25 Preliminary results February 11, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 26 Feb 11, 2001 Feb 12, 2001 Feb 13, 2001 Feb 14, 2001Feb 15, 2001 Feb 16, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 27 Feb 12, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 28 Feb 13, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 29 Feb 14, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 30 Feb 15, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 31 Feb 16, 2001

MCAO May 24-25, 2001 MCAO Preliminary Design Review 32 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 May 24-25, 2001 MCAO Preliminary Design Review 33 Sodium monitoring team Run #1 (Feb , 2001) –Laser: Laurent Michaille (IC) & Celine d’Orgeville –Telescopes: John Quartel & Nick Wooder (IC) Run #2 (May 2-10, 2001) –Laser: Celine d’Orgeville & Maxime Boccas (CTIO) –Telescopes: Brooke Gregory (CTIO) & Gelys Trancho Future runs (Sept., Nov./Dec and Feb. 2002) –Laser: Celine d’Orgeville … –Telescopes: Francois Rigaut, Brooke Gregory, Andrei Tokovinin, Gelys Trancho + others

MCAO May 24-25, 2001 MCAO Preliminary Design Review 34 PDR Agenda Friday, 5/ 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