adaptive optics in astronomy - portland state university | home
TRANSCRIPT
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Adaptive Optics in AstronomyAdaptive Optics in Astronomy
Jay McCarthyKeck II Telescope - Mauna Kea volcano in Hawaii
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Adaptive Optics vs. Active OpticsAdaptive Optics vs. Active Optics
Active Optics• Low Spatial Frequency• Effects Due to Temperature, Gravity, Tracking• Low Frequency Corrections < 0.05Hz
Adaptive Optics• Subset of Active Optics• High Spatial Frequency• Real time, closed-loop control• Effects due to atmospheric turbulence• Frequency Corrections are 1 – 1000Hz
WIYN 3.5 meter optical telescope Kitt Peak, AZ
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
““..perpetual tremor..”..perpetual tremor..”
Atmospheric Turbulence• Temperature fluctuations
causes wind velocity changes, eddies
• Atmospheric density differences
• Aerosol scattering, molecular absorption
• Tiny Lenses
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Optical Resolution LimitationsOptical Resolution Limitations
Plane Waves – Diffraction limitedR α λ/D
Atmospheric DistortionR α λ/ rO
Fried’s Coherence Length – rO• Turbulence scale size – wavefront
phase correlated• rO is on the order of 5-20cm
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Adaptive Optical System Design Adaptive Optical System Design
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
WavefrontWavefront Sensors Sensors –– ShackShack--Hartmann Hartmann
• Array of Lenses images to a CCD array
• Local gradient information determined by centroids
• Phase front reconstructed according to gradients
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Phase Reconstruction Phase Reconstruction
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Sensor CCD Sensitivity Sensor CCD Sensitivity –– Guide StarsGuide Stars
• Suppose each sensor requires 150 photons, ro is 15cm (at Keck), 100Hz sampling – require mv = 12
• Need bright object for wavefront sensor• Given 1.45*exp(0.96*mv) stars/rad2
• 150,000 stars/rad2
• Isoplanatic angle of 10µrad• 1.46x10-7 (mv = 12) stars/µrad
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Laser Guide StarsLaser Guide Stars
3 meter Lick Observatory Mt. Hamilton, California.
• Rayleigh Scattering – 20km• 150 phtons – 14mJ/pulse
(XeF, copper vapor)• Sodium Resonance – 92km
150 photons – 272mJ/pulse (Nd:YAG, excimer) 592nm
Higher altitude, more accurate phase representation
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Deformable MirrorsDeformable Mirrors
• Piston and Tilt• 336 actuators• Other designs: segmented,
piston only, tilt only
Multiple Mirror Telescope (MMT) Arizona
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Comparison of Images with and without AOComparison of Images with and without AO
Galaxy NGC 7469,
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Adaptive Optics for the Human EyeAdaptive Optics for the Human Eye
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Artificial Neural Networks in Adaptive OpticsArtificial Neural Networks in Adaptive Optics
• Currently used for wavefront reconstruction –centroid placement
InputHidden Layer
Output
•Nonlinear •I/O Mapping•Supervised Learning
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Adaptive Critic Control DesignAdaptive Critic Control Design
• Mirror control is nonlinear• Current control designs use linear controllers• Computationally expensive• Neural Networks are simple, low computational cost• Reinforcement learning• Can be used with ANN wavefront sensor to reduce
costs and time
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
Final RemarksFinal Remarks
• AO rejuvenate current land based telescope performance
• Retrofitting most land based telescopes > 4m• Can be used in Astronomy, Medical Applications,
and Telecommunications• ANN’s can improve controller performance and
reduce complexity
NW Computational Intelligence LaboratoryNW Computational Intelligence Laboratory
AO Projects/CompaniesAO Projects/Companies
• ADONIS on the ESO-La Silla 3.6 m telescope• (UH-AO) Hokupa at Mauna Kea and on the 8-m Gemini North• PUEO installed on the 3.6-m CFHT telescope (Mauna Kea)• ADOPT on the 100" Hooker telescope (Mount Wilson)• ALFA on the Calar Alto 3.5-m telescope• LLNL AO System at the 3.5-m Shane telescope (Lick Observatory• Keck II AO Facility at Mauna Kea• Companies: Stellar Products, TURN Ltd., Adaptive Optics
Associates, Inc., Starpoint Adaptive Optics, etc