Adaptive Optics:basic concepts, principles

and applications

Short course of lectures

Vadim Parfenov

Res.Ctr. “S.I.Vavilov State Optical Institute”

14, Birzhevaya linia, St.Petersburg, 199034, Russia

vadim@optilas.spb.ru

Lecture #2

Applications of Adaptive Optics.

New technologies. Future of AO

• Astronomy with Adaptive Optics;

• Non-Astronomical Applications of AO;

• Adaptive Optics in Ophtalmology;

• Other Applications of AO;

• New Technologies;

• Future of AO.

Outline

Adaptive optics technology

AO technology deals with real-time correction of optical aberrations.Used mainly in researchenvironment. Established applications:- Astronomy;- Military optical systems;- Laser technology;- Ophthalmology.

Part I

Astronomy with Adaptive Optics

Optical observations by ground-based astronomers have long been limited by the distorting effects of the Earth’s atmosphere.

Primary mirrors of telescopes have been polished to exquisite accuracy for telescopes with apertures as large as 10 meters, but at optical wavelengths these can deliver an angular resolution typically no better than of a 25-cm telescope, as atmospheric turbulence deforms the image on a millisecond time scale.

Two possible solutions of the problem:

1. Space Telescopes (Extremely expensive ! );2. Adaptive Optics Systems which measure and undo the effects of clear-air turbulence in real time.

I. Existing and funded Projects Some examples of adaptive optics systems currently

working for astronomy:

-        ESO-France-Come-On-Plus system at La Silla Observatory, Chile

(52 actuators on a 3.6-m telescope)

(this is improved version of an early prototype called Come-On)

(19 actuators on the ESO 3.6-m telescope));

  -        the University of Hawaii system at the Canada-France-Hawaii Telescope (CFHT)

on Mauna Kea, Hawaii, USA (12 actuators on a 3.6-m telescope);

- two 10-m Keck telescopes, Mauna Kea, Hawaii, USA (primary mirror consists of 36

hexagonal elements);

-        8.5-m Gemini North telescope product of a collaboration of the U.S.A., Canada, the United

Kingdom, Argentina, Brazil and Chile), Mauna Kea, Hawaii, USA;

-        8.3-m Subaru telescope, Mauna Kea, Hawaii, USA

-        a system on Sacramento Peak, New Mexico, USA, built by Lockheed for solar

observations(19 tip-tilt piston segments, that is 38 degrees of freedom, on a 0.7-m

telescope);

-        six-aperture Martini project on the 4.2-m William Herschel Telescope. La Palma.

-      ALFA system (  3.6-m telescope, Cala Alto, Spain).

Mount Mauna Kea, Hawaii, USA

KECK INTERFEROMETER

KECK TELESCOPE

PRIMARY MIRROR

General view of Keck interferometer

Telescope Subaru, Mount Mauna Kea, Hawaii

Trapezium region in the Orion nebula with adaptive optics off (a) and on (b) at the H wavelength of 0.6564 m. These images were obtained by the 1.5-m laser-guided adaptive optics telescope at the Starfire Optical Range in New Mexico. The central star, 1 Orionis, was used as the tip-tilt reference source. A majority of the faint objects are H sources associated with the photoevaporating envelopes of low-mass stars. Field of view is 41 x 41 arcsec, and spatial resolutions is 0.4 arcsec. (Image provided by R.Q.Fugate, Phillips Laboratory, and P.McCullough, University of Illinois.)

Some military adaptive optical telescopes are used for astronomical applications !

II. Where Do We Go From Here ?

(Some coming and Planning Projects of Astronomical telescopes)

ESO OWL (100 meter – class) Telescope

ESO OWL (100 meter – class) Telescope

ESO OWL (100 meter – class) Telescope

Optical design of the ESO OWL Telescope

3. 25-m Russian Astronomical Telescope AST-25

(Project of Res.Ctr. “Astrofizika”, Moscow)

Other projects of large astronomical adaptive telescopes

  1. 50-m Sweden adaptive astronomical telescope

2. Project of 30-m optical-infrared Telescope CELT (California Extremely Large Telescope)

THE JAMES WEBB SPACE TELESCOPE

JWST (formerly Next Generation Space telescope) will be a large, infrared-optimized adaptive space telescope. It will have an 18-segment, 6.5-meter primary mirror. It is being built by Northrop Grumman Space Technology and is scheduled to launch in 2011.

Part II

Non-Astronomical Applications of Adaptive Optics

1. Military Adaptive Optical Systems

• Imaging optical systems (satellites surveillance, etc.);

• Large-size telescopes for ground-based high-power laser energy projection;

• Large-size telescopes for space-based high-power laser energy projection.

Three views of the satellite Seasat from the U.S. Air Force Starfire Optical Range 3.5 m adaptive optical telescope (AF Kirtland Airbase, NM):

(a) through the turbulence, (b) real time correction using adaptive optical system, (c) post-processed with the blind deconvolution algorithm. 

2. Adaptive Optics in Ophthalmology

Historical remarks

• First investigations on the use of AO in ophthalmology have been carried out by David Williams from Rochester University, USA, in 1995-1996.

• First prototype of commercial AO fundus camera –result of joint researches of the Moscow State University, Russia (project manager –Dr. A.Larichev) & Kestrel Corp., USA, (project manager – Dr.L.John Otten) - 2002.

Measurement of human eye Measurement of human eye aberrationsaberrations

Short-sightedness Far-sightedness

Normal vision = emmetropia

Background

Technology is in its Lasik Infancy

keras (cornea) smileusis (carving)

Keratomileusis (cornea carving)

1949 – Professor Jose Ignnasio Barraquer of Colombia first suggested and made myopic keratomileusis.

Laser in situ keratomileusis (LASIK) is the most recent step in the process of removing/shaping corneal tissue. It combines well-established surgical techniques with the precision of excimer laser photoablation.

Although it enjoys at present great popularity among refractive surgeons, LASIK is a still still developing procedure In terms of technique and developing procedure In terms of technique and preoperative patient management.preoperative patient management.

Medical Need of Human Eye Aberrations Measurement

LASIK involves creating a corneal flap so that midstronal tissue can be ablated directly and reshaped with an excimer laser beam.

With the knowledge of the aberrations the custom ablation

pattern to compensate for the aberrations of the eye can be developed.

Because very little of the epithelium has been disturbed, most patients report only a few hours of discomfort after

having LASIK vision correction.

Basic Layout of Wavefront Sensing For the Human Eye

1L

2L

3L

7L

5L

6L

8L

10L

9L

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Principal scheme of Wavefront Analyzer for Human Eye Aberration Measurement

Images of human eye retina made by Adaptive Optical System

a) b) a) image made by AO fundus camera; b) the same image after following mathematical treatment

(Pictures have been taken with AO systems of the Lomonosv Moscow State University )

Preliminary conclusions

• AO technology is effective way to image retina

of human eye;• Effectiveness of AO approach has been

demonstrated; • Collaboration of Russian and American scientists

have resulted in development of first prototype of commercial fundus-camera;

• New era of human eye diagnostics is begun.

Human vision correction.Supervision ?

The main idea –

Correction of human eye by means of AO-based

spectacle lens and artificial eye implant

Two main goals:

1. Restoration of the accommodation ability of the human eye for two

target groups: with artificial eye implant and for elderly people

(contact lens)

2. Improvement of the visual acuity over the natural limit

(to be resarched).

Adaptive spectacles

G. Vdovin, Quick focusing of imaging optics using micro machined deformable mirrors, Opt. Comm., 140, pp. 187-190, (1997).

Preliminary conclusionsCommon knowledge:

• AO is applicable to the human eye and can increase the resolution of its optics

• AO should be conjugated to the eye lens, resulting in bulky and complicated setups

Proposed:• The only way to use AO for everyday vision correction is the

incorporation of the AO within the human eye. • There are two ways to incorporate the AO: a contact lens and

an intra-ocular implant.

Approach

Requirements to the implant

• Safe (low power low voltage);• Small and bio-compatible, chemically neutral;• Wireless control and feedback;• Temporal stability;• Transparent;• Polarization insensitive;• Usable with the control system off;• Transparent for oxygen (contact lens only).

Adaptive LC correctors

Adaptive LC correctors: small (5 to 10 mm), low power (less than 1 mW), safe, non-toxic, transparent (90%), usable with power off (no focusing power), durable.

Adaptive LC lens

Suggested implant configuration•Integrated receivercoil;•Integrated LC lens•Encapsulation:same as forocular implants;•Focusing powercontrolled by theamplitude and frequency of the control signal•With no control acts as a static implant

Preliminary conclusions:

What is required for AO human vision correction ?

• Development of a multi-channel wireless link to the implantable adaptive corrector;

• Development of the packaging approach for a LC corrector, both for the contact lens implementation and for the implant;

• Development of a wireless-powered and controlled “smart” adaptive optical component.

The technical goals are feasible in a wider sense than the final application-specific goals. They are in the streamline of the general development of the AO technology.

Other applications of Adaptive Optics

Moon

Receiver

Laser beacon

Earth

Retransmitter

mirror

1 2 34

567

3. Transmission of high-power energy in space

Multi-modular adaptive optical system 1- laser beam phase modulator; 2- amplifier, 3-phase sensor, 4- collimating telescope, 5 -frequency control, 6 - laser master oscillator, 7 - laser-heterodyne

4. Adaptive Optics power beaming for orbital debris removal

What is a problem ?

More than 160,000 or more objects larger than 1 cm in diameter in low-earth orbit. Space debris can damage spacecrafts ! But all space debris of the 1-10 cm can be removed by sufficient power ablating of ground-based pulsed lasers. AO system for laser beaming through atmosphere is necessary !

5. Deployable Space-Based LIDARs

Some examples:

1. 3-meter ORACLE (joint project of the NASA and Canadian Space Agency)Goal of the project – monitoring of Earth ozone Layer.

2. 3.5-meter Tektonika-A (project of Russian Academy of Sciences)Goal of the project – prevention of earthquakes.

6. Compensation of wavefront aberrationsof high-power laser beams

First works were carried out by Russian scientists:Yu.Anan`yev (Vavilov State Optical Institute),M.Vorontsov & A.Kudryashov (Moscow State University)

The goals are –1. Compensation of distortions of wavefront of high-power industrial lasers;2. Achievement of Super-Gaussian distribituion of laser beams

Correction of wave-front distortions of laser beams by means of the use of

deformable mirrors

                                                                            

The intensity distribution of high-power Nd:YAG laser in the focal plane of lens

overall size of the focal spot of corrected beam decreases by 3 times !

7. Scanning optical microscope

Micromachined deformable mirror significantly improves the scan resolution over the wide field ofview in the scanning microscope.

8. Adaptive pulse compression using micromachined deformable mirrors

Application of MMDM allows to compress the laser pulse from 150fsto about 15fs (close to the theoretical limit). Currently one of themost used methods of laser pulse compression.

Preliminary conclusions:

Now there are many applications of Adaptive Optics !

At present time there are several established applications:

- Astronomy; - Military optical optical imaging and high-power laser beaming systems; - Laser technology; - Ophthalmology.

• New approaches ?

• New technologies ?

• New applications ?

Part III.

Future of Adaptive Optics

New Technologies

1. MEMS-based Adaptive Optics

2. Membrane mirrors for space-

based optical telescopes

MOEMS-based Adaptive OpticsWhy MOEMS ?

Extremely large optical telescopes, ranging from 20 to 100 m are currently under development in different research groups around the world. For these telescopes the number of actuators for each deformable mirror, roughly equal to the number of r0 elements within the pupil, will range from 5000 to 100 000.

This number of actuators is prohibitive for conventional technology (stacked piezoelectric actuators, bimorph mirrors), but can be achieved by the development of new technologies based on optical micro-electro-mechanical systems (MOEMS).

Why MOEMS? (2)

• Three technologies apart are expensive. Single framework makes it simpler and cheaper to use.

• The precision of the structures is comparable to the light wavelength (350…1600nm)

Micromachined MembraneDeformable Mirrors

The shape of tensed membrane iscontrolled by the electrostaticattraction to the grid of electrodes

(developed by G.Vdovin,Delft Technical University, Netherlands)

Advantages of MOEMS-based Adaptive Optics System

Desired features:

• compactness (low weight, small size);

• simplicity (easy calibration and operation);

• speed (system frequency > 100 Hz);

• low cost (larger scope of applications).

ad a p tiv e m irro r

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co m p u ter

co r rec te dw av e fro n t

ab e rra te dw av e fro n t

b ea msp litte r

im a g e p la ne

im p e rfe c t m ed iu m

New Approaches

Radio plasma based artificial guide staras reference beacon foradaptive astronomical telescopes

1. 1. E.Ribak, Tomographic measurement of the atmosphere by artificial plasma fringes, European Southern Observatory Proceeding 55, 186-91 (1997).

2. 2. E Ribak, Alternative artificial guide stars for adaptive optics. SPIE 3353, 320-9 (1998).

Radio Guide Stars can be used for global tilt solution in optical and radio astronomical telescopes !

E.Ribak, R.Ragazzoni, and V.A.Parfenov, Radio plasma fringes as guide stars: tracking the global tilt, Proceedings of SPIE, Vol. 4338, p.118-126, (2000).

 

30-meter Diameter Diffraction-Limited Gossamer Telescopes in Space

Membrane (inflatable) mirror technology is underMembrane (inflatable) mirror technology is under

development at the U.S. Air-Force Research Laboratorydevelopment at the U.S. Air-Force Research Laboratory

Deployable membrane mirror in spaceDeployable membrane mirror in space(artistic view)(artistic view)

Adaptive Optics space- and ground-

based astronomical hypertelescopes

Large hypertelescopes – “multi-aperture densified-pupil imaging interferometers”. Consist of hundreds or thousands of mirror elements across a square kilometer or even 10 km.

Goal – general astro-physical imaging of deep-Universe galaxies.

Proposed by Antonie Laberyie (in Adaptive Optics, ESO Conference and Workshop Proceedings, No. 58, p.109-111. (2002) )

Conclusions:

AO is very promising optical technology which can be applicable to the astronomical telescopes and optical imaging systems and can increase the resolution of its optics.

There are many established applications of Adaptive Optics.

Now a number of new technologies and innovative concepts are under development. It will result in further improvement of Adaptive optical systems parameters.

Further development and wide use of AO will depend on cost of AO systems.

Future of Adaptive Optics is almost unlimited…