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 15

MCAOMCAOAligning the laser…Aligning the laser…

May 24-25, 2001 MCAO Preliminary Design Review 16

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Hole in the roof !Hole in the roof !

May 24-25, 2001 MCAO Preliminary Design Review 17

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Laser beam !!!Laser beam !!!

May 24-25, 2001 MCAO Preliminary Design Review 19

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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

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Preliminary resultsPreliminary results

Rayleigh scattering (< 30 km)

Sodium guide star (~ 90 km)

May 24-25, 2001 MCAO Preliminary Design Review 24

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Preliminary resultsPreliminary results

February 18, 2001 22:35-23:50

May 24-25, 2001 MCAO Preliminary Design Review 26

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Feb 11, 2001Feb 12, 2001Feb 13, 2001Feb 14, 2001Feb 15, 2001Feb 16, 2001

May 24-25, 2001 MCAO Preliminary Design Review 32

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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