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Sodium monitoring Sodium monitoring experiment in Chileexperiment in Chile
Céline d’OrgevilleCéline d’Orgeville
May 24-25, 2001 MCAO Preliminary Design Review 2
MCAOMCAO
Presentation overviewPresentation overview
• Sodium physics – Mesospheric sodium facts– Laser-sodium interaction basics
• Sodium monitoring experiment at CTIO– Experimental set-up– Pretty pictures – Preliminary results
May 24-25, 2001 MCAO Preliminary Design Review 4
MCAOMCAOMesospheric sodium Mesospheric sodium characteristicscharacteristics
• 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
MonthsNa
abun
danc
e (1
09 ato
ms/
cm2 )
Annual mean = 4.3 109 atoms/cm2
2
6
4
Sodium monitoring at Urbana, Illinois
May 24-25, 2001 MCAO Preliminary Design Review 5
MCAOMCAOImportance of sodium Importance of sodium parameters for AOparameters 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
May 24-25, 2001 MCAO Preliminary Design Review 6
MCAOMCAOImportance of sodium Importance of sodium parameters for AOparameters 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
May 24-25, 2001 MCAO Preliminary Design Review 7
MCAOMCAO
Sodium monitoring experimentSodium 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
May 24-25, 2001 MCAO Preliminary Design Review 8
MCAOMCAOSodium monitoring with a Sodium monitoring with a laser – just another laser guide laser – just another laser guide
starstar
May 24-25, 2001 MCAO Preliminary Design Review 9
MCAOMCAOSodium atoms / laser light Sodium atoms / laser light interaction physicsinteraction physics
F=2 F=3
D2 line:=589.0 nm
3P
3S 32S1/2
32P3/2
32P1/2
May 24-25, 2001 MCAO Preliminary Design Review 10
MCAOMCAO
Sodium atoms / laser light Sodium atoms / laser light interaction physicsinteraction 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)
Las
er b
andw
idth
(M
Hz)
XInefficient spectral format (bandwidth > 3 GHz) Max.
efficiency zone
Maximum efficiency at the 10-W levelX
XSaturation
Photon Photon returnreturnper Watt per Watt ofofCW laser CW laser powerpower
6
14
18
10
May 24-25, 2001 MCAO Preliminary Design Review 11
MCAOMCAO
Experimental set-upExperimental set-up
e ~ 10 km
h ~ 90 km
d0.9 ~ 140 m
dSchm ~ 110 m
~d e / h2 ~ 35 arcsec
CTIO 0.9m / Schmidt
0.9 m Schmidt
LASERLASER
May 24-25, 2001 MCAO Preliminary Design Review 14
MCAOMCAOOptical bench: laser + launch Optical bench: laser + launch towertower
May 24-25, 2001 MCAO Preliminary Design Review 19
MCAOMCAO
Experimental resolutionExperimental 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 ~ 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 h ~ 0.5-1.1 km
May 24-25, 2001 MCAO Preliminary Design Review 20
MCAOMCAO
Experimental resolutionExperimental 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 ~ 40where signal is the sum of binned pixel signal over LGS width Time (s)
SN
R
20 40 60
20
40
60
80
100
120LGS width = 3" bin = 2
May 24-25, 2001 MCAO Preliminary Design Review 22
MCAOMCAO
Preliminary resultsPreliminary results
Rayleigh scattering (< 30 km)
Sodium guide star (~ 90 km)
May 24-25, 2001 MCAO Preliminary Design Review 24
MCAOMCAO
Preliminary resultsPreliminary results
February 18, 2001 22:35-23:50
May 24-25, 2001 MCAO Preliminary Design Review 26
MCAOMCAO
Feb 11, 2001Feb 12, 2001Feb 13, 2001Feb 14, 2001Feb 15, 2001Feb 16, 2001
May 24-25, 2001 MCAO Preliminary Design Review 32
MCAOMCAO
Data reduction…on-goingData 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
May 24-25, 2001 MCAO Preliminary Design Review 34
MCAOMCAO
PDR AgendaPDR Agenda
Friday, 5/250800 Laser System 0900 CTIO Sodium Studies0915 Control System0945 Break1000 RTC Electronics1045 Safety System1100 Availability analysis1130 Closed vendor
Sessions1200 Lunch
1300 Cost and schedule1400 Committee session1700 Committee report1800 Adjourn
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