Rahul Krishnan Seminar Adaopt

822019 Rahul Krishnan Seminar Adaopt

httpslidepdfcomreaderfullrahul-krishnan-seminar-adaopt 126

An Introduction to AdaptiveOptics

BY

RAHUL KRISHNAN

S7 EEE



Why do we need adaptive optics

To Correct for Irregularities in theTransmission Media ndash Atmospheric (Astronomical)

Scintillation or Twinkling (Eddies ~ radicλL)

Beam Wander or Quiver (Eddies gt Beam Size)

Spreading (Eddies lt Beam Size)

ndash Atmospheric (LASER Transmission) Thermal Blooming

ndash Ocular (Retinal Imaging) Defects in the Lens and Cornea





Astronomical AO ExampleNeptune

415

Without adaptive optics With adaptive optics

2

3

a r c

s e c

Credit Keck Observatory LLNL UCB



Essentials of anAO system

Wavefront sensor

Computer

Phase modulator



How Turbulence Effects Light

Spherical wavesemitted by thesource (star) areessentially planewaves when theyarrive at the Earthrsquosatmosphere Thewaves are thenrandomly distorted

by turbulence in the



How does it work

Two Basic Functions

ndash Wavefront sensing

Shack-Hartmann wavefront sensor

Shearing interferometer

ndash Wavefront correction

Tip-tilt optical element

Deformable optical element



Wavefront Sensing

Shack-HartmannSensor

ndash Has become the

standard type of sensor ndash Uses an array of

spherical ldquolenseletsrdquo

ndash Focuses wavefronts

onto a CCD array ndash (b) is a plane wave

ndash (c) is a distorted wave



Wavefront Sensing

ShearingInterferometer

ndash Distorted wavefronts

result in phase shiftedoutput signals betweenthe detector arrays

ndash Two interferometers are

required for correctionin the x-y plane



Wavefront Correction

High speed tip-tiltmirror reduces overallwavefront tilt

Deformable mirror(monolithic orsegmented) correctswavefront shape



Wavefront Correction Monolithic Deformable Mirror

ndash Reflective face cast on a solid piezoelectric backing (14um)

ndash Thin face supported by an array of electro-mechanical actuators (+- 30um) ndash Thin face supported by an array of piezoelectric actuators (50um)




Segmented Mirrors

ndash Capable of largercorrections than

monolithic types ndash Requires frequent

calibration

ndash Diffraction due to gaps

between segments





Some Definitions

Apparent or VisualMagnitude ndash The relativebrightness of a star asseen by an observer on

Earth Guide Star ndash A sufficiently

bright star to use as areference for imagecompensation The

required magnitude variesas a function of the desiredobservation wavelength



Limitations of Image Compensation

Compensation in visible wavelengths (05um)requires a guide star of magnitude 10 or brighter

Compensation in infrared wavelengths (22um)

allows guide stars down to magnitude 14

Small isoplanatic region around the guide starlimits total observation area

ndash Visual ndash 1100000 of the sky ndash IR ndash 11000 of the sky



Guide Stars



Artificial Guide Stars

The area of sky coverage can beexpanded using artificial guide stars

Created using a LASER aligned withthe telescope optics

Rayleigh beacons take advantage ofRayleigh scattering in theatmosphere ndash Useful for telescopes with apertures lt 2m

ndash Creates a 1 to 2 arc second guide star 5 to

10km in altitude ndash 100W LASER

ndash LASER is pulsed so that backscatter can beeliminated by range gating




Sodium Beaconsexploit a layer ofsodium vapor in the

upper atmosphere ndash 10W LASER at 589nm

ndash Excites sodium atoms90 to 92 km in altitude

Photo - The Sodium laser launching

from the side of the LickObservatory 120 ShaneTelescope This is a 10 minute timeexposure - note the star trails




Natural guide starrequired for tiltcorrection

Limiting magnitude forguide star is about 20

Result is nearly 100

sky coverage



IR Stellar imaging from Lick

Observatory



Upper Left Io imagetaken with Keckadaptive optics K-band 22 micron

Upper Right Io imagebased on visible lighttaken with Galileospacecraft orbiter

Lower Left Io imagetaken with Keckadaptive optics L-band35micron

Lower Right Io imagetaken without Keckadaptive optics



The Lick Observatory CIS



Non-Astronomical Applications

Most of the current AOtechnology wasdeveloped by DARPA

during the Cold War toimage and shoot downsatellites with LASERweapons



Retinal Imaging



References

Carroll Joseph Daniel C Gray Austin Roorda David R Williams ldquoRecent Advances inRetinal Imaging with Adaptive Opticsrdquo Optics and Photonics News Jan 2005 p 36-42

Chaisson Eric and Steve McMillan Astronomy Today 4th Edition Prentice Hall UpperSaddle River NJ 2002

Florence Ronald The Perfect Machine Harper Collins New York NY 1994

Hardy John W Adaptive Optics for Astronomical Telescopes Oxford University PressNew York NY 1998

Hardy John W ldquoAdaptive Opticsrdquo Scientific American June 1994 p 60-65

Hecht Eugene Optics 4th Edition Addison-Wesley Reading MA 2002

Tyson Robert K Principles of Adaptive Optics 2nd Edition Academic Press San DiegoCA 1998

AdaptiveOpticscom 2002 Adaptive Optics Associates Inc httpwwwaoainccom Center for Adaptive Optics 2005 University of California Santa Cruz

httpcfaoucolickorg





Why do we need adaptive optics

To Correct for Irregularities in theTransmission Media ndash Atmospheric (Astronomical)

Scintillation or Twinkling (Eddies ~ radicλL)

Beam Wander or Quiver (Eddies gt Beam Size)

Spreading (Eddies lt Beam Size)

ndash Atmospheric (LASER Transmission) Thermal Blooming

ndash Ocular (Retinal Imaging) Defects in the Lens and Cornea






415


2

3

a r c

s e c





Wavefront sensor

Computer

Phase modulator








How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg








415


2

3

a r c

s e c





Wavefront sensor

Computer

Phase modulator








How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg






415


2

3

a r c

s e c





Wavefront sensor

Computer

Phase modulator








How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg






Wavefront sensor

Computer

Phase modulator








How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg










How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg





How does it work

Two Basic Functions









Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg





Wavefront Sensing










Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg





Wavefront Sensing



















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg
















Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg











Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg






Segmented Mirrors



calibration


between segments





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg







Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg





Some Definitions















Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg













Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg





Guide Stars
























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg


























sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg

















sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg









sky coverage




Observatory

















Retinal Imaging



References









httpcfaoucolickorg






Observatory

















Retinal Imaging



References









httpcfaoucolickorg



















Retinal Imaging



References









httpcfaoucolickorg













Retinal Imaging



References









httpcfaoucolickorg










Retinal Imaging



References









httpcfaoucolickorg





Retinal Imaging



References









httpcfaoucolickorg





References









httpcfaoucolickorg





Date post:	06-Apr-2018
Category:	Documents
Upload:	trimm123
View:	221 times
Download:	0 times

Rahul Krishnan Seminar Adaopt

Documents