“Twinkle, Twinkle Little Star”: An Introduction to Adaptive Optics

1. “Twinkle, Twinkle Little Star”:An Introduction to Adaptive Optics Mt. Hamilton Visitor’s Night July 28, 2001

2. Turbulence in the atmosphere limits the performance of astronomical telescopes • Turbulence is the reason why stars twinkle • More important for astronomy, turbulence spreads out the light from a star; makes it a blob rather than a point Even the largest ground-based astronomical telescopes have no better resolution than an 8" backyard telescope!

3. Lick Observatory, 1 m telescope “Perfect” image: diffraction limit of telescope Long exposure image Short exposure image Images of a bright star, Arcturus Distant stars should resemble “points,” if it weren’t for turbulence in Earth’s atmosphere

4. Turbulence changes rapidly with time Sequence of very short snapshots of a star. Movie is much slower than "real time."

5. How to correct for atmospheric blurring Measure details of blurring from “guide star” near the object you want to observe Light from both guide star and astronomical object is reflected from deformable mirror; distortions are removed Calculate (on a computer) the shape to apply to deformable mirror to correct blurring

6. Basic idea of AO Wavefront corrector Aberrated wavefront Corrected wavefront Wavefront sensor Wavefront control computer

7. Adaptiveopticsinaction Lick Observatory adaptive optics system Star with adaptive optics Star without adaptive optics

9. The Deformable Mirror

10. Deformable mirrors come in many shapes and sizes • Today: mirrors from Xinetics. From 13 to 900 actuators (degrees of freedom); 3 - 15 inches in diameter. Xinetics Inc.Devens, MA • Future: very smallmirrors (MEMS, LCDs); very large • mirrors (replace secondary mirror of the telescope)

11. Adaptive optics system is usually behind main telescope mirror • Example: AO system at Lick Observatory’s 3 m telescope Support for main telescope mirror Adaptive optics package under main mirror

12. What does a “real” adaptive optics system look like? Light from telescope Wavefront sensor Infra-red camera Deformable mirror

13. If there is no nearby star, make your own “star” using a laser Implementation Concept Lick Obs.

14. Laser in 120-inch dome

15. Laser guide star adaptive optics at Lick Observatory Uncorrected image of a star Laser Guide Star correction of a star: Strehl = 0.6 Ircal1129.fits RX J0258.3+1947 10/20/00 2:04 Ks V=15 K=~13.32 20s S=0.6 LGS

16. AO at the Keck 10 m Telescope Adaptive optics lives here

17. Adaptive optics on 10-m Keck II Telescope: Factor of 10 increase in spatial resolution 9th magnitude star imaged in infrared light (1.6 mm) Without AO Without AO width = 0.34 arc sec With AO width = 0.039 arc sec

20. Neptune in Infrared Light With Keck adaptive optics Without adaptive optics 2.3 arc sec May 24, 1999 June 27, 1999 l = 1.65 microns

21. Circumferential bands Compact southern features Neptune:Ground-based AO vs. Voyager Spacecraft Visible: Voyager 2 fly-by, 1989 Infrared: Keck adaptive optics, 2000

22. Saturn’s moon Titan: Shrouded by hazeas seen by Hubble Space Telescope Image at 0.85 microns Hints of surface detail Limb Brightening due to haze

23. Titan with adaptive optics Titan at Keck: with and without adaptive optics Titan without adaptive optics February 26-27, 1999 Typical @ wavelength 1.65 mm

24. Uranus as seen by Hubble Space Telescope and Keck AO Hubble Space Telescope false-color image (1.1, 1.6, 1.9 mm) Keck adaptive optics image (2.1 mm)

25. Keck AO Can See the Faintest RingsDiscovered by Voyager Voyager: 4 groups of rings Keck AO: outer e ring plus 3 inner groups (individual rings unresolved) e d g b a 4 5 6

26. 1 arc sec Volcano erupting on limb A volcano erupting on Io: Jupiter's largest moon Infrared image (2 microns)

27. Galileo: visible CCD camera Keck AO: three IR "colors" Io with adaptive optics sees most of the volcanic features seen by Galileo Same volcanoes Same volcanoes

28. Other Uses for AO • High-speed communications with laser beams • Cheaper and lighter telescopes in space • High-powered lasers for fusion power • Vision science research

29. Why Correct the Eye’s Optics? Perfect Eye Aberrated Eye

30. Visual Acuity Is Worse at Night When Pupils Dilate 1 mm 2 mm 3 mm 4 mm pupil images followed by psfs for changing pupil size 5 mm 6 mm 7 mm

31. The Rochester Adaptive Optics Ophthalmoscope

32. Adaptive optics provides a clear improvement in retinal image quality Point Spread Function Retinal Image in White Light Wave Aberration Retinal Image at 550nm Before adaptive optics: 1 deg After adaptive optics: YY 6.8 mm pupil

33. Adaptive optics provides highest resolution images of living human retina Williams, Roorda et al. (U Rochester) With AO: Resolve individual cones Without AO

34. Looking Inside the Eye with AO

35. View of Lunar Eclipse

36. Retinal Imaging – Basic Science Scale bar = 5 µm First images of the trichromatic photoreceptor mosaic in the human eye (Roorda and Williams, Nature, 1999)

38. Primary Mirrors: CELT vs. Keck Keck CELT

39. CELT and Stonehenge Keck

40. CELT in PacBell Park

41. Keep your eye on Adaptive Optics!

42. How to measure turbulent distortions (one method among many)

43. Applications and Results