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					Adaptive Optics and its Applications
             Lecture 1
               Neptune




             Claire Max
           UC Santa Cruz
           January 5, 2006


                                       Page 1
 Outline of lecture

• Introductions, goals of this course

• How the course will work

• Homework for next week

• Overview of adaptive optics for astronomy



   Please remind me to stop for a break at 2:45 pm!

                                                      Page 2
  Introductions: who are we?

• Via video:
  – AEOS, Maui: Ben Wheeler
  – Indiana U. Optometry School: Weihua Gao, Yan Zhang
  – JPL: Ian Crossfield
  – Keck Observatory: Eric Johansson, Roger Sumner
  – UCLA: Tuan Do, Jessica Lu, Jon Mauerhon, Emily
    Rice, Shelley Wright
  – UC Irvine: Lianqi Wang
  – UCSC Mt. Hamilton: Bryant Grigsby

• In the CfAO conference room at UCSC

                                                     Page 3
Videoconference techniques

• Please identify yourself when you speak
  – “This is Mary Smith from Santa Cruz”

• Report technical problems to the UCOP contact
  person (see your email)

• Microphones are quite sensitive
  – Do not to rustle papers in front of them
  – Mute your microphone if you are making side-
    comments, sneezes, eating lunch, whatever


                                                   Page 4
 Goals of this course

• To understand the main concepts behind adaptive
  optics systems
• To understand how to do astronomical observations
  with AO
   – Planning, reducing, and interpreting data (your own data, but
     just as importantly other people’s data)
   – Some of this will apply to AO for vision science as well

• Get acquainted with AO components in the Lab.
   – Delve into engineering details if you are interested.

• Brief introduction to non-astronomical applications
• I hope to interest a few of you in learning
  more AO, and doing research in the field
                                                                     Page 5
How the course will work

• Website: http://www.ucolick.org/~max/289C
  – Lectures will be on web after each class
  – (Hopefully before class)

• Textbooks

• Course components

• Homework



                                               Page 6
Required Textbooks

• Reader containing key articles and excerpts
  for this class. Available at Slug Books Coop,
  next to 7-11 Store. http://www.slugbooks.com/
  – We can arrange to buy copies on behalf of folks in
    video land
  – PDF versions will be available on restricted website

• Field Guide to Adaptive Optics by Robert K.
  Tyson and Benjamin W. Frazier, SPIE Press.
  Available from Bay Tree Bookstore.

                                                           Page 7
Course components

• Lectures
• Reading assignments
• Homework problems
• Student group projects (presentations in class)
• Laboratory exercises
• Field trip to Lick Observatory
• Web discussions (perhaps)
• Final exam
                                                    Page 8
Next Week

• Next Tuesday I will be at the American
  Astronomical Society meeting in Washington
  DC

• Instead of regular lecture class, there will be a
  tour of the Laboratory for Adaptive Optics

• Meet here in CfAO Conference Room at 2 pm

• Next regular class is Thursday January 12th


                                                      Page 9
Homework for Thursday January 12

• Read Syllabus carefully (on web)

• Do Homework # 1: “Tell me about yourself”

• Reading: in Reader
   –Chapter 1 of Roggeman (pages 59-66)
  – Excerpt from Hardy’s Chapter 2 (pages 5-15)
  – Don’t sweat the details -- goal is to get a broad
    overview on where adaptive optics came from



                                                        Page 10
Why is adaptive optics needed?


                         Turbulence in earth’s
                         atmosphere makes stars twinkle


                         More importantly, turbulence
                         spreads out light; makes it a
                         blob rather than a point




         Even the largest ground-based astronomical
  telescopes have no better resolution than an 8" telescope!
                                                               Page 11
 Images of a bright star, Arcturus


                     Lick Observatory, 1 m telescope

    ~ 1 arc sec
                                                         ~ l/D




  Long exposure               Short exposure             Image with
     image                        image                adaptive optics




Speckles (each is at diffraction limit of telescope)

                                                                         Page 12
 Turbulence changes rapidly with time

                 QuickTime™ and a YUV420 codec decompressor are needed to see this picture.




   Image is
  spread out
into speckles                                                                                 Centroid jumps
                                                                                                  around
                                                                                              (image motion)




     “Speckle images”: sequence of short snapshots of a star,
    taken at Lick Observatory using the IRCAL infra-red camera
                                                                                                          Page 13
Turbulence arises in several places

                        stratosphere


tropopause




    10-12 km


                            wind flow over dome
       boundary layer
                                                         ~ 1 km

                                        Heat sources w/in dome




                                                                  Page 14
Atmospheric perturbations
cause distorted wavefronts

                                   Rays not parallel




             Index of refraction
Plane Wave       variations          Distorted
                                     Wavefront

                                                       Page 15
 Optical consequences of turbulence

• Temperature fluctuations in small patches of air cause
  changes in index of refraction (like many little lenses)
• Light rays are refracted many times (by small amounts)
• When they reach telescope they are no longer parallel
• Hence rays can’t be focused to a point:



                          focus
                           Point
                                                               blur

   Parallel light rays             Light rays affected by turbulence
                                                                   Page 16
 Imaging through a perfect telescope

                                       With no turbulence,
                                        FWHM is diffraction limit
                                        of telescope,  ~ l / D
                      FWHM ~l/D
                                       Example:
                            1.22 l/D     l / D = 0.02 arc sec for
                                         l = 1 mm, D = 10 m

                                       With turbulence, image
                    in units of l/D     size gets much larger
                                        (typically 0.5 - 2 arc sec)
   Point Spread Function (PSF):
intensity profile from point source

                                                                    Page 17
 Characterize turbulence strength
 by quantity r0

  Wavefront
   of light

                               r0   “Fried’s parameter”

               Primary mirror of telescope


• “Coherence Length” r0 : distance over which optical
  phase distortion has mean square value of 1 rad2
  (r0 ~ 15 - 30 cm at good observing sites)

• Easy to remember: r0 = 10cm  FWHM = 1” at l = 0.5mm
                                                          Page 18
 Effect of turbulence on image size

• If telescope diameter D >> r0 , image size of a point
  source is l / r0 >> l / D

                    l/D
                                  “seeing disk”
                        l / r0


• r0 is diameter of the circular pupil for which the
  diffraction limited image and the seeing limited image
  have the same angular resolution.

• r0  10 inches at a good site. So any telescope larger
  than this has no better spatial resolution!
                                                           Page 19
How does adaptive optics help?
(cartoon approximation)
 Measure details of   Calculate (on a       Light from both guide
 blurring from        computer) the         star and astronomical
 “guide star” near    shape to apply to     object is reflected from
 the object you       deformable mirror     deformable mirror;
 want to observe      to correct blurring   distortions are removed




                                                                       Page 20
        Infra-red images of a star, from Lick
        Observatory adaptive optics system




     QuickTime™ and a YUV420 codec decompressor are needed to se e this picture.




            No adaptive optics                  With adaptive optics


Note: “colors” (blue, red, yellow, white) indicate increasing intensity
                                                                                   Page 21
AO produces point spread functions
with a “core” and “halo”
                                       Definition of “Strehl”:
                                      Ratio of peak intensity to
                                      that of “perfect” optical
                                               system
        Intensity




                       x

• When AO system performs well, more energy in core
• When AO system is stressed (poor seeing), halo
  contains larger fraction of energy (diameter ~ r0)
• Ratio between core and halo varies during night
                                                               Page 22
Adaptive optics increases peak
intensity of a point source
                                        Lick
                                        Observatory




      No AO     With AO
                           Intensity




        No AO                 With AO




                                                      Page 23
  Schematic of adaptive optics system




Feedback loop:
       next cycle
     corrects the
   (small) errors
of the last cycle




                                        Page 24
How to measure turbulent distortions
(one method among many)




        Shack-Hartmann wavefront sensor
                                          Page 25
 Shack-Hartmann wavefront sensor
 measures local “tilt” of wavefront

• Divide pupil into subapertures of size ~ r0
   – Number of subapertures  (D / r0)2

• Lenslet in each subaperture focuses incoming light to
  a spot on the wavefront sensor’s CCD detector

• Deviation of spot position from a perfectly square grid
  measures shape of incoming wavefront

• Wavefront reconstructor computer uses positions of
  spots to calculate voltages to send to deformable
  mirror
                                                            Page 26
 How a deformable mirror works
 (idealization)


         BEFORE                  AFTER




Incoming     Deformable    Corrected
Wave with      Mirror      Wavefront
Aberration
                                         Page 27
Real deformable mirrors have
continuous surfaces




• In practice, a small deformable mirror with
  a thin bendable face sheet is used

• Placed after the main telescope mirror
                                                Page 28
Deformable Mirror for real wavefronts
 Most deformable mirrors today
 have thin glass face-sheets
                       Glass face-sheet




Light                                     Cables leading to
                                            mirror’s power
                                            supply (where
                                          voltage is applied)



                                   PZT or PMN actuators:
                                   get longer and shorter
                                   as voltage is changed
  Anti-reflection coating
                                                                Page 30
 Deformable mirrors come in many sizes

 • Range from 13 to > 900 actuators (degrees of freedom)




                                                About 12”




A couple                           Xinetics
of inches
                                                       Page 31
 New developments:
 tiny deformable mirrors
• Potential for less cost per degree of freedom

• Liquid crystal devices
  – Voltage applied to back of each pixel changes index
    of refraction locally

• MEMS devices (micro-electro-mechanical
  systems)
  Electrostatically
  actuated                     Membrane
                    Attachment mirror
  diaphragm         post




          Continuous mirror

                                                          Page 32
 If there’s no close-by “real”
 star, create one with a laser


• Use a laser beam to
  create artificial
  “star” at altitude of
  100 km in
  atmosphere




                                 Page 33
 Laser is operating at Lick Observatory,
 being commissioned at Keck

                            Keck Observatory




Lick
Observatory
                                               Page 34
Galactic Center with Keck laser guide star

    Keck laser guide star AO   Best natural guide star AO




                                                            Page 35
Adaptive Optics World Tour




                             Page 36
Adaptive Optics World Tour
(2nd try)




                             Page 37
Steady growth in AO astronomy
publications since 1995




                                Page 38
Citations for AO papers are
equal to astrophysics average




                                Page 39
Astronomical observatories with
AO on 3-5 m telescopes

• ESO 3.6 m telescope, Chile

• Canada France Hawaii

• William Herschel Telescope, Canary Islands

• Mt. Wilson, CA

• Lick Observatory, CA

• Mt. Palomar, CA

• Calar Alto, Spain


                                               Page 40
Adaptive optics system is usually
behind main telescope mirror

 • Example: AO system at Lick Observatory’s 3 m
   telescope

Support for
     main
                                      Adaptive optics
 telescope
                                       package below
    mirror
                                        main mirror




                                                   Page 41
Lick adaptive optics system at 3m
Shane Telescope




                                              DM




                    Off-axis   IRCAL infra-
      Wavefront     parabola    red camera
       sensor        mirror                   Page 42
Palomar adaptive optics system



                         AO system is in
                         Cassegrain cage




  200” Hale telescope




                                           Page 45
Adaptive optics makes it possible to find
faint companions around bright stars

         Two images from Palomar of a
        brown dwarf companion to GL 105


                              200” telescope




             Credit: David Golimowski
                                               Page 46
    The new generation:
    adaptive optics on 8-10 m telescopes

                   Summit of Mauna Kea volcano in Hawaii:

                                                                  Subaru


                                                                  2 Kecks




Gemini North


               And at other places: MMT, VLT, LBT, Gemini South
                                                                            Page 47
 The Keck Telescope




 Adaptive
  optics
lives here




                      Page 48
    Keck Telescope’s primary mirror
    consists of 36 hexagonal segments




Nasmyth
platform




                                        Person!




                                              Page 49
Neptune in infra-red light (1.65 microns)

                                            With Keck
  Without adaptive optics                 adaptive optics




                            2.3 arc sec




      May 24, 1999                         June 27, 1999
                                                            Page 50
Neptune at 1.6 mm: Keck AO exceeds
resolution of Hubble Space Telescope

        HST - NICMOS                  Keck AO




                                                        ~2 arc sec
     2.4 meter telescope           10 meter telescope


              (Two different dates and times)
                                                                     Page 51
Uranus with Hubble Space
Telescope and Keck AO




                               L. Sromovsky


   HST, Visible                         Keck AO, IR

Lesson: Keck in near IR has same resolution as Hubble in visible

                                                                   Page 52
Uranus with Hubble Space
Telescope and Keck AO
                                de Pater




   HST, Visible                       Keck AO, IR

Lesson: Keck in near IR has same resolution as Hubble in visible

                                                                   Page 53
European Southern Observatory:
4 8-m Telescopes in Chile




                                 Page 54
 VLT NAOS AO first light

Cluster NGC 3603: IR AO on 8m ground-based telescope
 achieves same resolution as HST at 1/3 the wavelength




      Hubble Space Telescope      NAOS AO on VLT
        WFPC2, l = 800 nm          l = 2.3 microns       Page 55
 Some frontiers of adaptive optics

• Current systems (natural and laser guide stars):
   – How can we measure the Point Spread Function while we
     observe?
   – How accurate can we make our photometry? astrometry?
   – What methods will allow us to do high-precision spectroscopy
     with AO?


• Future systems:
   – Can we push new AO systems to achieve very high contrast
     ratios, to detect planets around nearby stars?
   – How can we achieve a wider AO field of view?
   – How can we do AO for visible light (replace Hubble on the
     ground)?
   – How can we do laser guide star AO on future 30-m telescopes?

                                                                    Page 56
Frontiers in AO technology

• New kinds of deformable mirrors with > 5000
  degree of freedom

• Wavefront sensors that can deal with this many
  degrees of freedom

• Innovative control algorithms

• “Tomographic wavefront reconstuction” using
  multiple laser guide stars

• New approaches to doing visible-light AO
                                                Page 57
 Adaptive optics at UCSC

• Center for Adaptive Optics
  – This building is headquarters
  – NSF Science and Technology Center
  – AO for astronomy and for looking into the living
    human eye
  – 11 other universities are members, as well as national
    labs and observatories

• Laboratory for Adaptive Optics
  – Funded by the Gordon and Betty Moore Foundation
  – Two labs in Thimann
  – Experiments on “Extreme AO” to search for planets,
    and on AO for Extremely Large Telescopes

                                                         Page 58
• Enjoy!




           Page 59

				
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