Monica Bobra, "The Endless Mantra: Innovation at the Keck Observatory"
Laser guide star adaptive optics at the Keck Observatory
14
Laser guide star adaptive optics at the Keck Observatory Adam R. Contos, Peter L. Wizinowich, Scott K. Hartman, David Le Mignant, Christopher R. Neyman, Paul J. Stomski, Jr., and Douglas Summers W.M. Keck Observatory SPIE Astronomical Telescopes and Instrumentation Conference 23 August 2002, Waikoloa, HI 4389 - 42
description
4389 - 42. Laser guide star adaptive optics at the Keck Observatory. Adam R. Contos, Peter L. Wizinowich, Scott K. Hartman, David Le Mignant, Christopher R. Neyman, Paul J. Stomski, Jr., and Douglas Summers W.M. Keck Observatory SPIE Astronomical Telescopes and Instrumentation Conference - PowerPoint PPT Presentation
Transcript of Laser guide star adaptive optics at the Keck Observatory
Laser guide star adaptive optics at
the Keck Observatory
Adam R. Contos, Peter L. Wizinowich, Scott K. Hartman, David Le Mignant, Christopher R.
Neyman, Paul J. Stomski, Jr., and Douglas Summers
W.M. Keck Observatory
SPIE Astronomical Telescopes and Instrumentation Conference
23 August 2002, Waikoloa, HI
4389 - 42
Talk Outline
OverviewSky Coverage for LGS and NGS ModesOptical PathNew LGS AO HardwareSystem Upgrades & IssuesLaser Guide StarFutureSummary
Overview
Traditional AO with NGS – Bright star in close proximity ~ 1% coverage– Sodium LGS for nearly complete coverage
• Still require an NGS, but can be much dimmer
Keck II System Upgrades for LGS AO– Low Bandwidth Wavefront Sensor (LBWFS)– Tip/Tilt Sensor (TTS), using quad-cell APDs– Software control– Laser system (described in following talk)
Scheduled for integration in 2003
Sky Coverage vs. NGS Limiting Magnitude(Varying Galactic Lat. and Field of View)
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
0.10% 1.00% 10.00% 100.00%
Sky Coverage
Re
fere
nc
e S
tar
Ma
gn
itu
de
(R
-ba
nd
)
30'' FOV @ 45º lat
60'' FOV @ 45º lat
60'' FOV @ 0º lat
Sky Coverage: NGS and LGS1Bahcall & Soneira, 1981; 2Keck Report 208, 1996.
NGS
LGS
Optical Path
Highlighted AO Bench Elements: 1-Image Rotator2-Tip/Tilt Mirror4-Deformable Mirror6-IR Dichroic12-Sodium Dichroic13-Field Steering Mirrors14, 15-Wavefront Sensing Camera
and Focus Camera Stage17-Beamsplitter18-Low Bandwidth Wavefront
Sensor, Tip/Tilt Sensor & Stage19-Acquisition Camera
LBWFS & TTS Description
Low Bandwidth Wavefront Sensor– Shack-Hartmann lenslet array sensor– 304 subapertures (240 active)– Photometrics 512x512 CCD detector– Readout every few sec. to few min.
Tip/tilt Sensor– Quad-lens– Fiber-fed APDs
Mounted on 3-axis tip/tilt stageBeamsplitter cube
– 90% to TTS, 10% to LBWFS
System Upgrades & Issues (1)
1no bright NGS
nearby LGS
2 laser spot moving WFS to Up-Tip/Tilt (laser pointing)
3wavefront changing
rapidly WFS to deformable
mirror loop
4laser spots elongated &
distorted in WFS
recalibrate using
LBWFS centroid & gains
5sodium distance
changing move WFS (focus)
6 pupil size changes motorized pupil relay optics
7sodium in science
camera
IR transmissive dichroic & science
filters
System Upgrades & Issues (2)
8no tip/tilt info; limited focus info; no 'truth'
calibrator
Dim NGS
9LGS wavefront will
drift w.r.t. NGS
LBWFS to determine avg.
wavefront (truth)
10LGS provides no tip/tilt information
quad cell TTS w/ APDs
11LGS focus will drift
w.r.t. NGS
LBWFS to determine best
focus
System Upgrades & Issues (3)
12NGS not co-located
w.r.t. LGS
LBWFS/TTS co-located on x,y,z
TSS stage
14
when move TSS, LBWFS looses registration with
deformable mirror
LBWFS lenslet mounted on x, y
stage
13see excess sodium
light in long exposures
sodium trasmissive dichroic & sodium rejection filter for
TTS/LBWFS
1st Laser Propagation (12/01)
Laser power ~ 17 W FWHM ~ 1.4” (seeing ~ 1”) Magnitude ~ 9.5
Future
Summary of LGS AO at Keck
Achieved first laser propagationAO upgrades being incorporated for LGSIntegration milestones throughout 2003
– LGS AO on world’s largest optical telescope will become incredible tool for astronomy
– First operational LGS on an 8-10 m telescope
System Flow & Control
