Research Network for Adaptive Optics
Australian Research Capacity
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Research in adaptive optics in Australia is spread throughout most of
the major universities, defence organizations, and nascent
industry. Here we consider what research capacity Australia
currently has in the area of adaptive optics, including its strengths
and potential opportunities for development.
The Research Network for Adaptive Optics embraces the following research areas:
 University of Sydney adaptive optics system at the Anglo-Australian Telescope. John O'Byrne spent several months in 2001 working with the astronomical Adaptive Optics group at the University of Durham, UK. His collaborations with groups in the UK have included SCIDAR measurements at Siding Spring Observatory with Imperial College London to begin characterizing atmospheric turbulence.
 Turbulence profile above Siding Spring Observatory obtained with SCIDAR. Courtesy John O'Byrne. Tip-tilt correction is also an integral part of the Sydney University Stellar Interferometer (SUSI). There is considerable experience in the SUSI group in building and controlling a tip-tilt system. Tip-tilt correction was also demonstrated in a laboratory-based scanning confocal microscope system. Attempts to utilise this adaptive optics experience in ophthalmology in conjunction with the Queensland University of Technology have not yet attracted ARC funding. As a result, the full potential of adaptive optics activity at the University of Sydney is yet to be realised. The Research School of Astronomy and Astrophysics (RSAA) of The Australian National University routinely operates a low-order tip-tilt secondary mirror system on the infrared Cassegrain focus of its 2.3 m telescope at Siding Spring Observatory. This system was developed by RSAA. It uses piezo-electric actuators to tip and tilt the 250-mm diameter telescope secondary mirror at frequencies up to 100 Hz. Position sensing is performed by an optical CCD in the telescope focal plane. A dichroic mirror reflects near-infrared light to the science instrument. Improvements in image full width at half maximum of up to a factor of two over natural seeing are realised in suitable atmospheric conditions.
 Schematic of the tip-tilt secondary system on the ANU 2.3 m telescope. The Research School of Astronomy and Astrophysics of The Australian National University has designed and is building two facility class adaptive optics instruments for the international Gemini Observatory. The group is led by Dr. Peter McGregor and includes ten engineers. The Near-infrared Integral Field Spectrograph (NIFS) will be used with the ALTAIR classical adaptive optics system on the 8-m diameter Gemini North telescope in HAWAII. ALTAIR will correct a field approximately 20 arcseconds in radius centered on its reference star. A laser guide star system is expected to be installed in early 2005, before NIFS is commissioned. NIFS will recorded a two-dimensional grid of near-infrared spectra at 0.1 arcsecond spatial resolution over the central 3.0x3.0 arcsecond of ALTAIR's field. The spectral resolving power of R ~ 5500 will be sufficient to separate terrestrial OH airglow emission lines and hence work in the low-background regions between the airglow lines.
 Peter McGregor aligning the Near-infrared Integral Field Spectrograph. The Gemini South Adaptive Optics Imager (GSAOI) is a diffraction-limited camera that will be the work horse instrument for the Gemini Observatory's flagship Multi-Conjugate Adaptive Optics (MCAO) system. The MCAO system will use five laser guide stars and three natural guide stars to sample and correct the three-dimensional structure of the atmosphere. Using this system, it will be possible to obtain diffraction-limited near-infrared images over a field approximately 90 arcseconds in diameter. GSAOI will record these images using a 4096x4096 pixel mosaic of Rockwell HAWAII-2RG detectors with a spatial sampling of 0.020 arcseconds per pixel. The diffraction-limit of an 8-m telescope is approximately 0.04 arcseconds at the middle of the near-infrared wavelength band.
 The Gemini South Adaptive Optics Imager camera assembly. Dr. McGregor is a member of the Gemini Adaptive Optics Science Working Group, and Prof. Warrick Couch of the University of New South Wales also has a keen interest in adaptive optics through his role as the Australian Gemini Project Scientist. Adaptive Optics will play a key role in the success of 30-100 m diameter Extremely Large Telescopes (ELT) that are current being considered world-wide. The Research School of Astronomy and Astrophysics of The Australian National University is committed to gaining significant access to an ELT for the Australian astronomical community. The School is therefore planning to address issues associated with deploying adaptive optics systems on ELTs. An active adaptive optics group exists at the University of Cantebury, Christchurch, New Zealand. The group consists of Dr. Richard Lane, Dr. Peter Cottrell, a part-time postdoc and three PhD students. The main objective of the group is astronomical imaging. Their main research activities are:
The Astronomy group at the University of New South Wales (Prof. John Storey, A/Prof. Michael Ashley, A/Prof. Michael Burton, and Dr. Jon Lawrence) have deployed a fast tip-tilt secondary mirror on the SPIREX telescope at the South Pole. SPIREX was the first infrared telescope to operate from the Antarctic plateau, and demonstrated the feasibility of operating complex astronomical telescopes with adaptive optics capability under Antarctic conditions. Working with the University of Nice, the UNSW group has made the first microthermal measurements of the distibution of turbulence throughout the Antarctic atmosphere, creating a database that now forms the basis for research by adaptive optics groups around the world on potential Antarctic telescopes. The UNSW group is now studying the adaptive optics requirements for large telescopes in Antarctica. Jon Lawrence, in particular, is investigating the optimization of adaptive optics for a possible Antarctic ELT. In addition, the group is continuing to make extensive measurements of the turbulence properties of the Antarctic atmosphere, in collaboration with the University of Nice, the Jet Propulsion Laboratory in California, and the USA Cerro Tololo Inter-American Observatory in Chile. A new collaboration with the Osservatorio Astrofisico di Arcetri in Italy will explore issues related to adaptive optics for an Antarctic-based ELT. The UNSW group currently holds a 5 year ARC Discovery Projects grant and Jon Lawrence holds a separate ARC APD grant. Astronomical adaptive optics systems with wide field of view require multiple artificial laser guide stars to simultaneously measure the wavefront errors through different atmospheric paths. The most promising approach is to stimulate sodium atoms in the upper atmosphere using a laser locked to the Na I D transition in the yellow region of the optical spectrum. Highly collimated lasers with laser powers of approximately 10 Watts are required to produce sufficiently bright laser guide stars. Prof. Barry Luther-Davies at The Research School of Physical Sciences and Engineering at The Australian National University is attempting with Electro Optics Systems Ltd, a nearby NSW company, to develop a high-powered, low-maintenace sodium laser that can be deployed at remote observatory sites. There are several approaches to creating laser guide stars. Probably the most favoured at present relies on non-linear sum frequency generation from the output of two synchronously mode-locked Nd:YAG lasers operating on the 1064 nm and 1319 nm lines of Nd:YAG. Whilst this scheme does use a very well developed laser system, it is rather complex and not well suited for "remote" operation and is complex to scale to higher average power. The ANU group therefore propose to use a periodically poled Optical Parametric Oscillator (OPO) as an alternative route to generating high power at 589 nm. This scheme is attractive as the pump source remains a Nd:YAG or Nd:YVO4 laser which is a well-developed system but can use simpler mode-locking schemes which should simplify the system and render it more capable of reliable remote operation. Additionally, the group's current laser products allow them to access some unique high power laser technology from the Fraunhofer Institute in Aachenm, Germany. As a result they can access laser hardware that potentially allows the OPO-based system to be scaled beyond the 15 W initial specification towards the 100 W level. This is probably not needed for astronomical observations, but may well be important for the satellite ranging work of Electro Optic Systems Ltd. Prof. Jesper Munch and Dr. Peter Veitch at the Department of Physics of the University of Adelaide have recently submitted a proposal for the research and development of a sodium guide star source. Their novel design is optimized to produce pulsed waveforms suitable for use in Multi-Conjugate Adaptive Optics on Extremely Large Telescopes. It is power scalable to average powers in excess of 100 Watts and builds upon their extensive experience with the development of high power, diffraction-limited beam quality, solid state lasers for remote sensing. Wavefront sensors and deformable mirrors are key elements of an adaptive optics system. However, complex mathematics in the form of a reconstructor is needed to convert wavefront information into actuator commands at the deformable mirror. The reconstructor solves a linear system of equations. To be effective, the solution must be found in real time with minimal latency. The only way to meet such a requirement is to use tools and techniques that are at the forefront of both the mathematical and computer sciences. These techniques include optimal solution methods such as the multigrid method or near optimal methods like the preconditioned conjugate gradient method. To obtain the maximum possible performance, cache based implementations of the algorithms need to be used as they help avoid the memory bottleneck inherent in modern computing systems. Much of this technology has been developed for the solution of large scale problems on supercomputers. Dr. Linda Stals at the Department of Mathematics at The Australian National University is interested in transferring this technology to the area of adaptive optics to solve "real life" practical problems.
This work would be assisted greatly by the addition of adaptive optics, which would permit the imaging of individual photoreceptors in the retinal array. By using two or more wavelengths, it will be possible to identify the spectral sensitivity of the individual cone photoreceptors. This would in turn permit optical stimulation of the separate cone arrays (e.g., "red-sensitive" and "green-sensitive" cones) independently, in order to separate their electrical responses in a way that has not previously been possible. The expectation is that there will be great scope for research on the retina (photoreceptors and post-receptoral cells) using these techniques. However, this is virgin territory so it is difficult to forecast what might be discovered. Dr. Fred Reinholz has been a visiting scientist at the Center for Visual Science at the University of Rochester. Within the group "Adaptive Optics for the Human Eye", headed by Prof. David Williams, Dr. Reinholz has led efforts to develop a high-resolution scanning laser ophthalmoscope employing segmented MEMS mirrors as the adaptive optical elements. He has now returned to the Lion's Eye Institute in Perth. David Atchison is an Associate Professor at the School of Optometry at the Queensland Institute of Technology. He has taught and researched in the area of visual optics for many years. He measures aberrations in the eye and their effects on human visual performance (e.g., contrast sensitivity, visual acuity). His interest in adaptive optics is in eliminating and manipulating aberrations of the eye and then ascertaining the effects of doing this on measures of visual performance such as visual acuity, the contrast sensitivity function, and the phase transfer function. He plans to set up an adaptive optics facility using relatively inexpensive MEMS mirrors to perform this work. Most of the components are in-hand. Technical expertise could be made available through collaborations with Prof. Pablo Artal at the University of Murcia, Spain. Prof. Atchison's interest in adaptive optics is related to recent advances in corneal refractive surgery. Many ophthalmologists are confident of providing "Supervision" by customising corneal ablations to correct the eye's monochromatic aberrations. Everyone is a potential patient, not just those with manifest refractive errors such as myopia (short sightedness). However, until it can be demonstrated that experimental or clinical measurements match predictions of visual performance, we cannot be confident that such procedures will match the expectations. Prof. Atchison has had significant collaborations with Prof. George Smith of the The Department of Optometry and Vision Sciences at the University of Melbourne in various ocular optics endeavours funded by the ARC and NHMRC. Prof. Smith has obtained a Queensland University of Technology Visiting Research Fellowship to work with Prof. Atchison in 2004. Dr. Andrew Metha of The Department of Optometry and Vision Sciences at the University of Melbourne has worked with Prof. David Williams at the Center for Visual Science at the University of Rochester. He is setting up an adaptive optics corrected scanning laser ophthalmoscope along with Prof. George Smith, Dr. Ross Ashman (Hon. Fellow), and Mary Daaboul (Hons. student). Ross Ashman is building a Shack-Hartmann wavefront sensor for measuring the aberrations of the eye. This will form the first half of the adaptive optics system that the group would like to use for measuring and then correcting such aberrations to allow high resolution imaging of the retina. Specifically, this system could be used to explore the following ocular applications:
 Artist's impression of laser communications between Mars and Earth. Courtesy AAO.
Adaptive optics has typically been used in optical systems for viewing, and for improving the image viewed. The use of adaptive optics on the laser beam or in the laser rsonator, enabling real-time adjustment of the laser properties, is timely. The ability to adjust the laser beam profile in real time, for example to adapt to changes in a substrate for laser machining, perhaps as circumstances in the laser target change, is of great value in a wide range of laser applications. The project involves the development of deformable mirrors using laser microfabrication to improve the control and reproducibility of the structures. A long term aim of this group is to achieve real-time control of the frequency and spatial distribution of the laser output. The first stage of this program, an Honours project in 2004, is to demonstrate an electrically-controlled deformable mirror controlling the output from a diode-pumped microchip laser.
 Research in the Centre for Lasers and Applications has focussed on both the physics and the practical applications of lasers. In particular, several staff and students have expertise in the characterization and control of UV, visible, and infrared laser beam quality for various applications including laser microfabrication and imaging. The use of adaptive optics techniques for improving the beam quality is a natural extension of their work on modelling and characterising the outputs from a wide range of lasers. Real-time control of laser parameters offers great potential for improved sensitivity, efficiency, and selectivity in laser applications such as spectroscopy, communications, and remote sensing. Such lasers could be designed with specific properties, or in the longer term, the adjustment may be done by real-time optimization. For a laser, a smoothly deformable mirror with low mass and fine spatial resolution is required. The possibilities include; deformable membrane mirrors, segmented micro-mirrors, or liquid crystal spatial light modulators. Since all intra-cavity laser optics must be low-loss, with mm-dimension apertures for beam acceptance and smooth mirror surfaces, and a high damage threshold, the deformable membrane mirrors are most promising for use with laser beams. An intra-cavity deformable mirror is preferred, as smaller adjustments are required to correct beam aberrations than for external mirrors. The pixelated nature of segmented mirrors is often a significant problem for lasers, so it is more practical to use a continuous membrane where different areas of the membrane are deformed by actuators attached to the back of the mirror. Deformable mirrors for lasers can be made of any material that has satisfactory reflectivity and responds to electrostatic attraction or repulsion, e.g., thin smooth semiconductor films are suitable membranes, offer localised electrostatic response, and they can be metal- or dielectric-coated to give efficient broadband reflectivity. Clear parallels exist with the laser adaptive optics needed to produce highly-collimated, intense laser guide stars for astronomy and similarly high-collimated laser beams for satellite and space debris ranging and tracking. Prof. Min Gu at the Centre for Micro-Photonics at the Swinburne University of Technology heads a group building a laser tweezers system using donut beams. This device uses a static phase pattern generated by a liquid crystal display to produce the donut beam. They would like to use a dynamic system to control trapped particles. Areas of future development include:
Prof. Gu is a member of the Executive Committee and the Coordinator of the Melbourne node of the Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS). He holds an ARC Linkage Infrastructure Equipment & Facilities (LIEF) grant with Ross Ashmann entitled "Real Time Multi-Dimensional Multi-Photon Microscopy Facility".
These Directed Infrared Laser Countermeasures (DIRCM) systems are mounted on the aircraft fuselage as pods. These devices are used to deliver countermeasures against infrared guided missiles. The relevant aspects are:
The observed effects (lateral shifts, blurring, and scintillation) within the optical tracker is likely to be correlated with the outgoing laser effects (lateral shifts, laser broadening, and scintillation). The two bore-sighted apertures (laser and infrared camera) are separated by about 10 cm. The optical path is therefore very similar. The Electro-Optic Countermeasures group would like to develop improved DIRCM technologies and techniques. One of the potential approaches is to apply adaptive optics to the optical focussing of the incoming image of the missile plume and similarly the outgoing laser beam. (assuming a similar wavefront distortion across a similar optical path and likewise related corrective measures). The small bright and distant missile plume will act as the "guide star". It is assumed that this guide star moves along a smooth (non-erratic) track and grows in size and intensity by approximately 1/R2 (where R is the range, which decreases in time). This missile "guide star" will be imaged at a high frame rate by the camera. The adaptive optic components (mirror steering and deformation) would "hopefully" respond to compensate for turbulence-induced aberrations in the wavefront from the incoming "guide-star" image and the equivalent correction will be made for the outgoing laser beam. A more accurate track of the missile should be achieved and greatly improved laser beam should be delivered through strong turbulence. A complete cure-all is not expected, but it should be possible to obtain significant improvement in cases of moderate to strong turbulence.
Some areas for which they are investigating the use of adaptive optics are:
The broad direction of the group for the future is to apply the simple, low-cost adaptive optics system that might be developed in the current project to other time-varying aberrations problems such as:
A group at the Physics Department of the University of Auckland, New Zealand, led by Dr. Tom Barnes also studies various adaptive optics techniques. They are interested in the use of feedback interferometry for real-time aberration correction. They have recently demonstrated correction over a terrestrial path using feedback interferometry. They are also interested in the development of novel high speed interferometers (including phase-stepping and heterodyne white light systems) for use in adaptive optics. For this they have developed a range of self-referencing interferometers for adaptive optics applications using phase-stepping, heterodyne, and Fourier transform techniques. The group also designs and constructs segmented mirrors using low-cost techniques developed in-house. They are also interested in the application of membrane mirrors and liquid crystal devices. A group at the School of Information Technology and Electrical Engineering at the Australian Defence Force Academy works on wide-area algorithms that are useful for characterising turbulence at observatory sites and engineering adaptive optic components for wide-area AO systems. The group consists of two academics (Dr. Donald Fraser and Dr. Andrew Lambert), an ARC Research Associate/Professional Engineer (Sayyah Jahromi), a PhD student (Tahtali) and an ME student (Clyde). Their research interest is the restoration of atmospherically distorted images over a wide field of view. The group's research to date has involved post-capture image processing of turbulence degraded imagery with small, wide-field of view telescopes, in both astronomy and surveillance through heat haze. These both suffer viewing in the anisoplanatic regime. The key to wide-area restoration continues to be effective image registration, allowing us to dewarp each frame of a position-dependent tip-tilt distorted image sequence to remove local motion blur. Blind deconvolution then forms the last stage of image restoration, following motion deblurring. The group has also postulated that, in the anisoplanatic case, the random turbulence-induced tip-tilt may allow higher spatial frequencies than otherwise to enter the telescope pupil, leading to super-resolution. They have engineered a fast streaming camera (>100,000 frames/sec) based on a megapixel CMOS photosensor that will enable them to "freeze" atmospheric effects during daytime surveillance image experiments. In addition, they now have the ability to obtain simultaneous dual-camera image sequences for phase diversity experiments in anisoplanatic restoration. Investigations conducted in this fashion include a DSTO collaboration on the visual effects of Turbulent Plumes from Jet Engines. Incorporated in the work has been development and exploitation of spatial light modulators for adaptive optics. So far, these have been sideline investigations to the main image processing focus, but the group has long realised the need to develop multi-conjugate adaptive optics (MCAO) systems that would expedite the correction for, and visualisation of, the intervening turbulence. Until recently the expense of adaptive optics has restrained this avenue of investigation, even though the group feels that their post-processing algorithms would be adaptable to optical methods. Their experience in spatial light modulator technology using LCD, DMD, and more recently coated peizo-electric films is evolving into an inexpensive opportunity to produce fast quality deformable mirrors for use in a MCAO system. |
