Adaptive Optics (AO) is an ensemble of techniques that aims at the remedial of the deleterious effects that the Earth's
turbulent atmosphere induces on both imagery and signal gathering in real time. It has been over four decades since the
first AO system was developed and tested. During this time important technological advances have changed profoundly
the way that we think and develop AO systems. The use of Micro-Electro-Mechanical-Systems (MEMS) devices and
Liquid Crystal Devices (LCD) has revolutionized these technologies making possible to go from very expensive, very
large and power consuming systems to very compact and inexpensive systems. These changes have rendered AO
systems useful and applicable in other fields ranging from medical imaging to industry. In this paper we will review the
research efforts at the Naval research Laboratory (NRL) to develop AO systems based on both MEMs and LCD in order
to produce more compact and light weight AO systems.
The Naval Prototype Optical Interferometer (NPOI) is the longest baseline at visible wavelengths interferometer in the
world. The astronomical capabilities of such an instrument are being exploited and recent results will be presented. NPOI
is also the largest optical telescope belonging to the US Department of Defense with a maximum baseline of 435 meter
has a resolution that is approximately 181 times the resolution attainable by the Hubble Space Telescope (HST) and 118
times the resolution attainable by the Advanced Electro-Optical System (AEOS). It is also the only optical interferometer
capable of recombining up to six apertures simultaneously. The NPOI is a sparse aperture and its sensitivity is limited by
the size of the unit aperture, currently that size is 0.5 meters. In order to increase the overall sensitivity of the instrument
a program was started to manufacture larger, 1.4 meter, ultra-light telescopes. The lightness of the telescopes
requirement is due to the fact that telescopes have to be easily transportable in order to reconfigure the array. For this
reason a program was started three years ago to investigate the feasibility of manufacturing Carbon Fiber Reinforced
Polymer (CFRP) telescopes, including the optics. Furthermore, since the unit apertures are now much larger than r0 there
is a need to compensate the aperture with adaptive optics (AO). Since the need for mobility of the telescopes, compact
AO systems, based on Micro-Electro-Mechanical-Systems (MEMS), have been developed. This paper will present the
status of our adaptive optics system and some of the results attained so far with it.
The use of Spatial Light Modulators (SLM), Liquid Crystal Devices for atmospheric turbulence simulation in
optical system has increased in the recent years. These devices allow the development of test-beds that can be
used to simulate, analyze and improve optical components or systems in a controlled laboratory environment
before further implementation on the eld. Most research has been performed at visible wavelengths with
the use of a vast array of atmospheric turbulence simulation algorithms. We present preliminary work on an
atmospheric simulation test bed which uses an algorithm developed at NRL with a transmissive high denition
Liquid Crystal Device SLMs for applications in the short-wavelength infrared, with the main focus of interested
at 1550nm. Preliminary results are shown for the application to a high denition re
ective Liquid Crystal Device
SLM for the same wavelength.
Adaptive optics (AO) systems are well demonstrated in the literature with both laboratory and real-world systems being
developed. Some of these systems have employed MEMS deformable mirrors as their active corrective element. More
recent work in AO for astronomical applications has focused on providing correction in more than one conjugate plane.
Additionally, horizontal path AO systems are exploring correction in multiple conjugate planes. This provides
challenges for a laboratory system as the aberrations need to be generated and corrected in more than one plane in the
optical system. Our work with compact AO systems employing MEMS technology in addition to liquid crystal spatial
light modulator (SLM) driven aberration generators has been scaled up to a two conjugate plane testbed. Using two
SLM based aberration generators and two separate wavefront sensors, the system can apply correction with two MEMS
deformable mirrors. The challenges in such a system are to properly match non-identical components and weight the
correction algorithm for correcting in two planes. This paper demonstrates preliminary results and analysis with this
system with wavefront data and residual error measurements.
For the past decade our group has been involved in the development and test of small
portable Adaptive Optics (AO) systems based on MEMs Deformable Mirrors (DM)
technology. The main trust of this activity was toward what is usually referred as vertical
propagation of the light that is the common situation for astronomical applications.
However, in the past couple of years our efforts have been towards the correction of
horizontal path imagery. In this regime the atmospheric turbulence presents different
types of problems such to make the development of AO systems much more demanding.
Once again one of the starting points for us is the development of a test bed where AO
components and algorithms can be tested under well controlled conditions.
The Naval Prototype Optical Interferometer (NPOI) is the longest baseline interferometer operating at visible
wavelengths in the world. The astronomical capabilities of such an instrument are being exploited and recent results will
be presented. NPOI is also the largest optical telescope belonging to the US Department of Defense with a maximum
baseline of 435 meter has a resolution that is approximately 181 times the resolution attainable by the Hubble Space
Telescope (HST) and 118 times the resolution attainable by the Advanced Electro-Optical System (AEOS). It is also the
only optical interferometer capable of recombining up to six apertures simultaneously. The NPOI is a sparse aperture and
its sensitivity is limited by the size of the unit aperture, currently that size is 0.5 meters. In order to increase the overall
sensitivity of the instrument a program was started to manufacture larger, 1.4 meter, ultra-light telescopes. The lightness
of the telescopes requirement is due to the fact that telescopes have to be easily transportable in order to reconfigure the
array. For this reason a program was started three years ago to investigate the feasibility of manufacturing Carbon Fiber
Reinforced Polymer (CFRP) telescopes, including the optics. Furthermore, since the unit apertures are now much larger
than r0 there is a need to compensate the aperture with adaptive optics (AO). Since the need for mobility of the
telescopes, compact AO systems, based on Micro-Electro-Mechanical-Systems (MEMS), have been developed. This
paper will present the status of our adaptive optics system and some of the results attained so far with it.
Adaptive optics systems have advanced considerably over the past decade and have become common tools
for optical engineers. The most recent advances in adaptive optics technology have lead to significant
reductions in the cost of most of the key components. Most significantly, the cost of deformable elements
and wavefront sensor components have dropped to the point where multiple deformable mirrors and Shack-
Hartmann array based wavefront sensor cameras can be included in a single system. Matched with the
appropriate hardware and software, formidable systems can be operating in nearly any sized research
laboratory. The significant advancement of MEMS deformable mirrors has made them very popular for use
as the active corrective element in multi-conjugate adaptive optics systems so that, in particular for
astronomical applications, this allows correction in more than one plane. The NRL compact AO system and
atmospheric simulation systems has now been expanded to support Multi Conjugate Adaptive Optics
(MCAO), taking advantage of using the liquid crystal spatial light modulator (SLM) driven aberration
generators in two conjugate planes that are well separated spatially. Thus, by using two SLM based
aberration generators and two separate wavefront sensors, the system can measure and apply wavefront
correction with two MEMS deformable mirrors. This paper describes the multi-conjugate adaptive optics
system and the testing and calibration of the system and demonstrates preliminary results with this system.
Our program for the upgrade of the Naval Prototype Optical Interferometer with large telescopes
and adaptive optics has produced a test-bed for the in system evaluation and testing of our MEMs
adaptive optics components and system performances. We have already reported in recent
publications the basic characteristics of the test-bed. In order to improve the capabilities of such
laboratory set-up we have started an upgrade that aims at developing a Multi Conjugate Adaptive
Optics (MCA) test-bed. This test bed is based on the use of multiple Liquid Crystal Spatial Light
Modulators (LCSLMs) for producing different phase screens at different spatial locations within the
set-up. Details of this new set-up are presented in another paper in these proceedings. This paper
specifically deals with the analytic portion of the MCAO test-bed.
The Naval Prototype Optical Interferometer (NPOI) is the longest baseline at visible
wavelengths interferometer in the world. The astronomical capabilities of such an
instrument are being exploited and recent results will be presented. NPOI is also the
largest optical telescope belonging to the US Department of Defense with a maximum
baseline of 435 meter has a resolution that is approximately 181 times the resolution
attainable by the Hubble Space Telescope (HST) and 118 times the resolution attainable
by the Advanced Electro-Optical System (AEOS). It is also the only optical
interferometer capable of recombining up to six apertures simultaneously. The NPOI is a
sparse aperture and its sensitivity is limited by the size of the unit aperture, currently that
size is 0.5 meters. In order to increase the overall sensitivity of the instrument a program
was started to manufacture larger, 1.4 meter, ultra-light telescopes. The lightness of the
telescopes requirement is due to the fact that telescopes have to be easily transportable in
order to reconfigure the array. For this reason a program was started three years ago to
investigate the feasibility of manufacturing Carbon Fiber Reinforced Polymer (CFRP)
telescopes, including the optics. Furthermore, since the unit apertures are now much
larger than r0 there is a need to compensate the aperture with adaptive optics (AO). Since
the need for mobility of the telescopes, compact AO systems, based on Micro-Electro-
Mechanical-Systems (MEMS), have been developed. This paper will present the status of
our adaptive optics system and some of the results attained so far with it.
The Naval Research Laboratory (NRL) has been conducting research
in novel portable adaptive optics systems for many years. These systems
are tested exhaustively in a laboratory environment before being migrated
to field experiments on astronomical telescopes. As part of the laboratory
testing, an atmosphere simulator hardware testbed has been developed to
provide a realization of atmospheric turbulence based on Kolmogorov
statistics. In this testbed, a high-pixel count liquid crystal spatial light
modulator induces the atmospheric turbulence through a series of
computer calculated phase maps. User controls allow a wide range of
telescope apertures and seeing conditions to be explored for testing the
adaptive optics system. This paper explains and reports on the use of this
dynamic and expandable system in characterizing the performance and
optimization parameters of the adaptive optics systems at NRL.
The Naval Research Laboratory (NRL) has been conducting research
in novel portable adaptive optics systems for many years. These systems
are tested exhaustively in a laboratory environment before being migrated
to field experiments on astronomical telescopes. As part of the laboratory
testing, an atmosphere simulator hardware testbed has been developed to
provide a realization of atmospheric turbulence based on Kolmogorov
statistics. In this testbed, a high-pixel count liquid crystal spatial light
modulator induces the atmospheric turbulence through a series of
computer calculated phase maps. User controls allow a wide range of
telescope apertures and seeing conditions to be explored for testing the
adaptive optics system. This paper explains and reports on the use of this
dynamic and expandable system in characterizing the performance and
optimization parameters of the adaptive optics systems at NRL.
The Naval Prototype Optical Interferometer (NPOI) is the longest baseline at visible wavelengths interferometer in the world. The astronomical capabilities of such an instrument are being exploited and recent results will be presented. NPOI is also the largest optical telescope belonging to the US Department of Defense with a maximum baseline of 435 meter has a resolution that is approximately 181 times the resolution attainable by the Hubble Space Telescope (HST) and 118 times the resolution attainable by the Advanced Electro-Optical System (AEOS). It is also the only optical interferometer capable of recombining up to six apertures simultaneously. The NPOI is a sparse aperture and its sensitivity is limited by the size of the unit aperture, currently that size is 0.5 meters. In order to increase the overall sensitivity of the instrument a program was started to manufacture larger, 1.4 meter, ultra-light telescopes. The lightness of the telescopes requirement is due to the fact that telescopes have to be easily transportable in order to reconfigure the array. For this reason a program was started three years ago to investigate the feasibility of manufacturing Carbon Fiber Reinforced Polymer (CFRP) telescopes, including the optics. Furthermore, since the unit apertures are now much larger than r0 there is a need to compensate the aperture with adaptive optics (AO). Since the need for mobility of the telescopes, compact AO systems, based on Micro-Electro-Mechanical-Systems (MEMS), have been developed. This paper will present the status of our adaptive optics system and some of the results attained so far with it.
Many electro optical devices are now available for compensating atmospheric distortions in optical systems. To support the characterization of these devices in a consistent fashion a common testbed that physically simulates these atmospheric aberrations is required. This paper reports on a system that realizes seeing conditions ranging from very poor to excellent and feeds these wavefronts to the compensation device under test. The testbed provides quantitative characterization of the system under test and evaluates residual wavefront error.
Deployment costs of large aperture systems in space or near-space are directly related to the weight of the system. In
order to minimize the weight of conventional primary mirrors and simultaneously achieve an agile system that is capable
of a wider field-of-view (FOV) and true optical zoom without macroscopic moving parts, we are proposing a
revolutionary alternative to conventional zoom systems where moving lenses/mirrors and gimbals are replaced with
lightweight carbon fiber reinforced polymer (CFRP) variable radius-of-curvature mirrors (VRMs) and MEMS
deformable mirrors (DMs). CFRP and MEMS DMs can provide a variable effective focal length, generating the
flexibility in system magnification that is normally accomplished with mechanical motion. By adjusting the actuation of
the CFRP VRM and MEMS DM in concert, the focal lengths of these adjustable elements, and thus the magnification of
the whole system, can be changed without macroscopic moving parts on a millisecond time scale. In addition, adding
optical tilt and higher order aberration correction will allow us to image off-axis, providing additional flexibility.
Sandia National Laboratories, the Naval Research Laboratory, Narrascape, Inc., and Composite Mirror Applications,
Inc. are at the forefront of active optics research, leading the development of active systems for foveated imaging, active
optical zoom, phase diversity, and actively enhanced multi-spectral imaging. Integrating active elements into an
imaging system can simultaneously reduce the size and weight of the system, while increasing capability and flexibility.
In this paper, we present recent progress in developing active optical (aka nonmechanical) zoom and MEMS based
foveated imaging for active imaging with a focus on the operationally responsive space application.
Many devices are now being used in Adaptive Optics Systems for compensating atmospheric
distortions. We have developed a testbed that simulates atmospheric aberrations using a Liquid
Crystal Spatial Light Modulator and the speed in which they vary may be controlled. This system
allows the simulation of seeing conditions ranging from very poor to very good and these aberrations
to be compensated by a second device. This second device may be a deformable mirror in
conjunction with an Adaptive Optics System. Using these two devices simultaneously provides a
well-defined quantitative characterization of the system and residual wavefront error using Point
Spread Function and interferometric techniques.
The use of adaptive and active optics (AO) is enabling the construction and test of flexible optical systems with
performances unprecedented. This flourishing of technical advances is also due to the availability of new technologies
that are much lower in cost, much easier to implement and use. Among these new technologies the use of Micro-Electro-
Machined (MEM) mirrors is one of the primary sources of innovation. Several groups are actively working in bringing to
fruition AO systems based on MEMs technologies and at the same time several groups are working to improve the
MEMs technology and tailor it more and more towards various aspects of the AO problems. This technology is
especially interesting to the Navy Prototype Optical Interferometer (NPOI) upgrade. In this field several AO systems
have to be constructed and operated. It is of the outmost importance that each system has a less complex and costly
approach than classical AO systems.
Sandia National Laboratory has constructed several segmented MEMS
deformable mirrors that are under investigation for their suitability in Adaptive Optics
systems for the Naval Research Laboratory. These mirrors are constructed in a
hexagonal array and have been constructed with flat surfaces, or with optical power
allowing each mirror to bring its subaperture of light to a focus similar to a Shack-
Hartman array. Each mirror can use the tip, tilt and piston function to move the focused
spots to the desired reference location, and the measurement of the applied voltage can be
used directly to power a similar flat MEMS deformable mirror. This paper reports on the
suitability of this reflective wavefront sensor for closed-loop Adaptive Optics
applications.
The development of sensors that are compact, lighter weight, and adaptive is critical for the success of future military initiatives. Space-based systems need the flexibility of a wide FOV for surveillance while simultaneously maintaining high-resolution for threat identification and tracking from a single, nonmechanical imaging system. In order to meet these stringent requirements, the military needs revolutionary alternatives to conventional imaging systems.
We will present recent progress in active optical (aka nonmechanical) zoom for space applications. Active optical zoom uses multiple active optics elements to change the magnification of the imaging system. In order to optically vary the magnification of an imaging system, continuous mechanical zoom systems require multiple optical elements and use fine mechanical motion to precisely adjust the separations between individual or groups of elements. By incorporating active elements into the optical design, we have designed, demonstrated, and patented imaging systems that are capable of variable optical magnification with no macroscopic moving parts.
Liquid crystal spatial light modulators, lenses, and bandpass filters are becoming increasingly capable as material and electronics development continues to improve device performance and reduce fabrication costs. These devices are being utilized in a number of imaging applications in order to improve the performance and flexibility of the system while simultaneously reducing the size and weight compared to a conventional lens. We will present recent progress at Sandia National Laboratories in developing foveated imaging, active optical (aka nonmechanical) zoom, and enhanced multi-spectral imaging systems using liquid crystal devices.
Adaptive optics systems are commonly added onto conventional astronomical telescopes to improve the wavefront quality in the presence of atmospheric turbulence. Recent successes in the development of carbon fiber reinforced polymer telescopes have significantly reduced the weight of meter class telescopes making them portable, however, most adaptive optics systems continue to be constructed on large optical benches. The Navy Prototype Optical Interferometer is developing several 1.4 m portable telescope with internal wavefront correction. As part of this upgrade, a prototype 0.4 m aperture telescope has been constructed and a light weight, compact adaptive optics system is being developed. We present in this paper the design of an adaptive optics system for the lightweight telescope. The key to this system is the incorporation of a compact wavefront correction device and a novel collimation optic within the base of the telescope.
This paper reports on the measurement and reconstruction using two algorithms of an Adaptive Tilt Mirror's (ATM) reflected wavefront using a Shack-Hartmann (SH) based wavefront sensor. The ATM consists of a deformable mirror mounted onto a fast steering mirror platform. Reconstruction of the wavefront was performed using Finite Difference and Finite Element reconstruction algorithms for comparison. The SH wavefront sensor with high frame-rate readout camera and the two types of software reconstructors provide a visualization of the ATM's surface while being moved physically on the fast steering mirror platform at a rate of 30 Hz.
In most adaptive optics systems, there are two elements that control wavefront correction. These are a tip/tilt platform and a deformable mirror. The tip/tilt platform can correct the lower order aberrations like piston, tip and tilt. The deformable mirror can correct the higher order aberrations like defocus, astigmatism, etc. By mounting the deformable mirror onto the tip/tilt platform, one corrective element is now used in the system, rather than two. This is made possible by the use of a lightweight MEMS deformable mirror, as traditional deformable mirrors tend to be quite large and bulky. Other advantages are that there is less overall optics and a simpler alignment process needed with this configuration.
In this paper we present results using a compact, portable adaptive optics system. Such compact systems are possible thanks to the use of new technologies based on Micro-Electro-Machined deformable mirrors and liquid crystals devices among other possible technologies. In the paper we will illustrate our experience with such devices; we will address the pros and cons of such approach, some experimental results and new trends for future tests.
Unique liquid crystal (LC) spatial light modulators (SLM) are being developed for foveated imaging systems that provide wide field-of-view (FOV) coverage (±60° in azimuth and elevation) without requiring gimbals or other mechanical scanners. Recently, a transmissive-SLM- based system operating in the visible (532 nm) has been demonstrated. The LC SLM development is addressing implementation issues through the development of high figure-of-merit (FoM) LC materials and transmissive high-resolution SLMs. Transmissive SLM operation allows the foveated imaging configuration to be very compact using a very simple lens system. The reduction in the size, weight and cost of the imaging optics and in data acquisition/processing hardware makes the foveated approach attractive for small platforms such as unmanned airborne vehicles (UAVs) or missile seekers.
KEYWORDS: Microelectromechanical systems, Mirrors, Analog electronics, Adaptive optics, Deformable mirrors, Control systems, Manufacturing, Commercial off the shelf technology, Actuators, Electronics
The use of Micro-Electro-Machined (MEM) devices as deformable mirrors (DM) for active and adaptive optics is increasing dramatically. Such increases are due to both the cost and simplicity of use of these devices. Our experience with MEM DMs has been positive, however the controlling protocols of these devices presents some issues. Based on our experience and needs we decided to design a generic controller based on a fast communication protocol. These requirements have pushed us to design a system around a USB 2.0 protocol. In this paper we present our architectural design for such controller. We present also experimental data and analysis on the performance of the controller. We describe the pros and cons of such approach versus other techniques. We will address how general such architecture is and how portable is to other systems.
In most adaptive optics systems, there are two elements that control wavefront correction, a fast steering mirror that corrects tip and tilt and a deformable element that corrects higher order aberrations. By mounting the deformable element onto the tip/tilt platform, complete wavefront compensation is now possible at one location in an optical system. The advantage of mounting a lightweight Micro Electro-Machined (MEM) deformable mirror on a tip/tilt stage is both fewer optical components and a simpler alignment process. The impact on the frequency stability of the of the MEM device on the tip/tilt platform is approximately 5% of the driving frequency.
The use of adaptive and active optics (AO) is enabling the construction and test of flexible optical systems with performances unprecedented. This flourishing of technical advances is also due to the availability of new technologies that are much lower in cost, much easier to implement and use. Among these new technologies the use of Micro-Electro-Machined (MEM) mirrors is one of the primary sources of innovation. Several groups are actively working in bringing to fruition AO systems based on MEMs technologies and at the same time several groups are working to improve the MEMs technology and tailor it more and more towards various aspects of the AO problems. In this paper we will presents an overview of MEMs adaptive optics problems. We will especially focus on our experience in this field and discuss results from our AO system. We will discuss pros and cons on the use of MEM for adaptive optics and elaborate on our experience on field-testing of these devices. This paper will also briefly discuss the broader use of adaptive optics in fields other than atmospheric compensation.
Adaptive optics techniques have been demonstrated in both laboratory and field tests, with a great level of scientific satisfaction, especially in astronomical and surveillance communities. Such successes have sparked the interest for these techniques in other fields, like biomedical imaging and industrial applications. However, to decrease complexity and costs, both very important issues for applications other than astronomical and surveillance, new technologies have to be brought to fruition. MEMS are becoming a very important player in this arena. We describe a portable adaptive optics (AO) system based on a MEM device that has been tested in both laboratory and field experiments. Results of these tests are discussed. Capabilities and shortcomings of this technology are discussed. A look at future applications and trends is given.
Modern microprocessors are rapidly reaching performance levels that make them suitable for wavefront sensing and correction. This has the combined advantage of reducing system costs and a smaller footprint for the control system. These reductions have provided adaptive optics system designers with the capability of producing small form factor and low power system compared to just a few years ago. In recent work on the NRL portable adaptive optics system, our group has investigated implementing alternative computer peripherals for deformable and tip/tilt mirror control to support the low power low cost approach. This paper reports on characterization of several computer peripherals for use within adaptive optics systems with a focus on minimizing size, weight, cost and power consumption.
This paper presents the optical design and experimental demonstration of a compact, foveated, wide field-of-view (FOV) imaging system using two lenses and a liquid crystal spatial light modulator (SLM). The FOV of this simple doublet system is dramatically improved by the SLM, which can be programmed to correct all the geometrical aberrations at any particular field angle. The SLM creates a variation in the image quality across the entire FOV, with a diffraction-limited performance at the field angle of interest (similar to the foveated human vision). The region of interest can be changed dynamically, such that any area within the FOV of the system can be highly resolved within milliseconds. The wide FOV, compactness, and absence of moving parts make this system a good candidate for tracking and surveillance applications. We designed an f/7.7 system, with a 60° full FOV, and a 27 mm effective focal length. Only two lenses and a beam splitter cube were used along with a reflective SLM. The theoretical wavefront aberration coefficients were used to program the SLM, which was placed in the pupil plane of the system. A prototype was built and the system was experimentally demonstrated using monochromatic light and a CCD camera.
Changing the field-of-view of a laser communication system in real-time without mechanical motion could significantly improve signal strength and reduce drop out rates. By incorporating active elements into the optical design, we have designed and demonstrated imaging systems that are capable of variable effective focal lengths with no macroscopic moving parts (i.e. active optical zoom). This technique, in which the active optics serve as variable focal-length lenses, could easily be applied to laser communication systems to improve capability. The key to this concept is to create relatively large changes in the field-of-view of the system with very small changes in the focal lengths of individual elements by leveraging the optical power of conventional optical elements surrounding the active optics. By appropriately designing the optical system, these variable focal-length lenses can provide the flexibility necessary to change the overall system focal length, and therefore field-of-view, that is normally accomplished with mechanical motion in conventional zoom systems.
Micromachined deformable membrane mirrors (MDMMs) are currently being integrated into or proposed for numerous space-based imaging applications, including systems that utilize phase diversity, foveated imaging, and active or adaptive optical zoom. In stark contrast to applications that require only a few waves of optical stroke, such as atmospheric turbulence correction, these applications often require that the mirrors operate over much larger dynamic ranges. In order to obtain near diffraction-limited performance, these mirrors must be capable of producing wavefronts with accurate figures to within a quarter-wave (P-V). Recent experimental results will be discussed, in which MDMMs produced focal lengths as low as 2.5m with near diffraction-limited performance.
In order to optically vary the magnification of an imaging system, continuous mechanical zoom lenses require multiple optical elements and use fine mechanical motion to precisely adjust the separations between individual or groups of lenses. By incorporating active elements into the optical design, we have designed and demonstrated imaging systems that are capable of variable optical magnification with no macroscopic moving parts. Changing the effective focal length and magnification of an imaging system can be accomplished by adeptly positioning two or more active optics in the optical design and appropriately adjusting the optical power of those elements. In this application, the active optics (e.g. liquid crystal spatial light modulators or deformable mirrors) serve as variable focal-length lenses. Unfortunately, the range over which currently available devices can operate (i.e. their dynamic range) is relatively small. Therefore, the key to this concept is to create large changes in the effective focal length of the system with very small changes in the focal lengths of individual elements by leveraging the optical power of conventional optical elements surrounding the active optics. By appropriately designing the optical system, these variable focal-length lenses can provide the flexibility necessary to change the overall system focal length, and therefore magnification, that is normally accomplished with mechanical motion in conventional zoom lenses.
Adaptive optics techniques have been proved in both laboratory and field tests to the satisfaction especially of the astronomical and surveillance communities. Such success have sparked interests in other fields, however, to increase efficiency and lower costs new technologies have to be brought to fruition. MEMs are becoming a very important player in this arena. In this paper we describe a portable adaptive optics (AO) system that has been tested in both laboratory and field experiments. Results of these tests will be discussed. Capabilities and shortcomings of this technology will be discussed. A look at future applications and trends will be given.
This report focuses on the treatment parameters leading to successful nanoshell-assisted photo-thermal therapy (NAPT). NAPT takes advantage of the strong near infrared (NIR) absorption of gold-silica nanoshells, a new class of nanoparticles with tunable optical absorptivities that are capable of passive extravasation from the abnormal tumor vasculature due to their nanoscale size. Under controlled conditions nanoshells accumulate in tumors with superior efficiency compared to surrounding tissues. For this treatment: (1) tumors were inoculated in immune-competent mice by subcutaneous injection, (2) polyethylene glycol coated nanoshells (≈150 nm diameter) with peak optical absorption in the NIR were intravenously injected and allowed to circulate for 6 - 48 hours, and (3) tumors were then extracorporeally illuminated with a collimated diode laser (808 nm, 2-6 W/cm2, 2-4 min). Nanoshell accumulations were quantitatively assessed in tumors and surrounding tissues using neutron activation analysis for gold. In order to assess temperature elevation, laser therapies were monitored in real-time using a mid-infrared thermal sensor. NAPT resulted in complete tumor regression in >90% of the subjects. This simple, non-invasive procedure shows great promise as a technique for selective photo-thermal tumor treatment.
In most adaptive optics systems, there are two elements that control wavefront correction. These are a tip/tilt platform and a deformable mirror. The tip/tilt platform can correct the lower order aberrations like piston, tip and tilt. The deformable mirror can correct the higher order aberrations like defocus, coma, spherical, etc. Currently in this method, two conjugate planes must be created by the two elements. It is also a necessity that these two conjugate planes be identical. This requires more optics and a more complicated alignment process. In this project a deformable mirror is mounted onto a tip/tilt platform resulting in the two correction elements having the same conjugate plane, automatically. This is made possible by the use of a lightweight deformable mirror, as traditional deformable mirrors tend to be quite large and bulky. Results of this experimental project will be presented.
Adaptive optics techniques have been proved in both laboratory and field tests to the satisfaction especially of the astronomical and surveillance communities. Such success have sparked interests in other fields, however, to increase efficiency and lower costs new technologies have to be brought to fruition. MEMs are becoming a very important player in this arena. In this paper we describe a portable adaptive optics (AO) system that has been tested in both laboratory and field experiments. Results of these tests will be discussed. Capabilities and shortcomings of this technology will be discussed. A look at future applications and trends will be given.
In this paper, we present results on a test-bed for the use of adaptive optics (AO) in optical interferometry. The test-bed is based on two deformable mirrors made by OKO technologies. The two mirrors are simultaneously controlled by the same computer and control software. The experimental set is based on our portable adaptive optics system. The goal of this test-bed is to study and characterize the effects of aberrations on the fringe contrast and the effects and characterization of the use of AO for improving fringe contrast. In this paper we will report some field test of our portable AO system. We will also describe the test-bed and some of the experimental results obtained so far.
In order to optically vary the magnification of an imaging system, mechanical zoom lenses, such as those found on 35mm cameras, require multiple optical elements and use cams or gears to adjust the spacing between individual or groups of lenses. By incorporating active elements in the optical design, we can eliminate the need to change lens separations and create an imaging system with variable optical magnification that has no macroscopic moving parts.
Adaptive optics techniques have been proved in both laboratory and field tests to the satisfaction especially of the astronomical and surveillance communities. Such success have sparked interests in other fields, however, to increase efficiency and lower costs new technologies have to be brought to fruition. MEMs are becoming a very important player in this arena. In this paper we describe a portable adaptive optics (AO) system that has been tested in both laboratory and field experiments. Results of these tests will be discussed. Capabilities and shortcomings of this technology will be discussed. A look at future applications and trends will be given.
The idea of using liquid crystal devices as an adaptive optics component has been proposed by several authors. In recent years a vigorous research effort has been carried out, and it is still flourishing, in several countries. Mainly the research and experimental work has been concentrated in the USA, U.K. and Russia. There are several reasons why liquid crystals may represent a valid alternative to the traditional deformable mirror technology that has been used for the past two decades or so. The main attractiveness of LC resides in the cost. Current deformable mirror technology has a range of price going from $2K to $15K per channel. LC technology promises to be at least a couple of orders of magnitude cheaper. Other reasons are connected with reliability, low power consumption and with a huge technological momentum based on a wide variety of industrial applications. In this paper we present some preliminary characterizations of a new, large format device. Such devices have the potential for extremely high-resolution wave-front control due to the over 10,000 corrective elements. The characterization of the device, so far, consists of measurements of the overall optical quality and of the phase control relationship
In this paper we present results using a compact, portable adaptive optics system. The system was developed as a joint venture between the Naval Research Laboratory, Air Force Research Laboratory, and two small, New Mexico based-businesses. The system has a footprint of 18x24x18 inches and weighs less than 100 lbs. Key hardware design characteristics enable portability, easy mounting, and stable alignment. The system also enables quick calibration procedures, stable performance, and automatic adaptability to various pupil configurations. The system was tested during an engineering run in late July 2002 at the Naval Observatory Flagstaff Station one-meter telescope. Weather prevented extensive testing and the seeing during the run was marginal but a sufficient opportunity was provided for proof-of-concept, initial characterization of closed loop performance, and to start addressing some of the most pressing engineering and scientific issues.
A University/Industry/Air Force Laboratory collaboration has developed an inexpensive but innovative telescope for interferometry. It incorporates low weight mirrors, low profile tip/tilt secondary, and accelerometer based jitter control. It is built to incorporate higher order adaptive optics. A design team has striven to emphasize a low cost medium tech approach to reduce costs coupled with sturdy precision engineering. The telescopes will be sited in New Mexico and used for Academic and Defense needs.
We have successfully demonstrated a simple, wide field-of- view, foveated imaging system utilizing a liquid crystal spatial light modulator (SLM). The SLM was used to correct the off-axis aberrations that otherwise limited the useful field-of-view (FOV) of our system. Our system mimics the operation of the human eye by creating an image with variable spatial resolution and could be made significantly smaller and more compact than a conventional wide FOV system. It may be useful in applications such as surveillance, remote navigation of unmanned vehicles, and target acquisition and tracking, or any application where size, weight, or data transmission bandwidth is critical.
KEYWORDS: Mirrors, Relays, Space telescopes, Telescopes, Beam controllers, Space mirrors, Laser applications, Satellites, Space operations, Space based lasers
EAGLE (Evolutionary Air & Space Global Laser Engagement) is the proposed high power weapon system with a high power laser source, a relay mirror constellation, and the necessary ground and communications links. The relay mirror itself will be a satellite composed of two optically-coupled telescopes/mirrors used to redirect laser energy from ground, air, or space based laser sources to distant points on the earth or space. The receiver telescope captures the incoming energy, relays it through an optical system that cleans up the beam, then a separate transmitter telescope/mirror redirects the laser energy at the desired target. Not only is it a key component in extending the range of DoD's current laser weapon systems, it also enables ancillary missions. Furthermore, if the vacuum of space is utilized, then the atmospheric effects on the laser beam propagation will be greatly attenuated. Finally, several critical technologies are being developed to make the EAGLE/Relay Mirror concept a reality, and the Relay Mirror Technology Development Program was set up to address them. This paper will discuss each critical technology, the current state of the work, and the future implications of this program.
The idea of using liquid crystal as adaptive optics components has been proposed by several authors. In recent years a vigorous research effort has been carried out, and it is still flourishing, in several countries. Mainly the research and experimental work has been concentrated in US, U.K. and Russia. There are several reasons why liquid crystal may represent a valid alternative to the traditional deformable mirror technology that has been used for the past two decades or so. The main attractiveness of LC is resides in the cost. Current deformable mirror technology has a range of price going from $2K to $15K per channel. LC technology promises to be at least a couple of orders of magnitude cheaper. Other reasons are connected with reliability, low power consumption and with a huge technological momentum based on a wide variety of industrial applications. In this paper I present some of the experimental results of a 5 years, on going, research effort at the Air Force Research Lab. Most of the work has been on the development of suitable devices with extremely high optical quality, individually addressable pixels, fast switching time. The bulk of the work has been concentrated in the arena of the untwisted nematic material. However new devices are now under development using dual-frequency nematic material and high tilt angle ferroelectric material.
In many instances, mechanical vibrations, not atmospherics, are the dominant contributors to time varying optical tilts affecting both astronomical and terrestrial observations. We used a pair of inexpensive micromachined accelerometers placed on the secondary mirror mount of a 12' telescope, inferring angular deviations from twice temporally integrated acceleration signals. We then applied this result with appropriate gain to a feed-forward tip/tilt mirror correction loop with good results.
We seek to examine near-IR photometric signatures for geosynchronous earth orbit (GEO) communication satellites. To this end, we present a set of high quality photometric measurements for a sample of ten GEOs. The observations were made with a standard set of broad band astronomical filters (Johnson filters), using the 3.6 meter telescope at the Air Force Research Laboratory (AFRL) Directed Energy Directorate Starfire Optical Range, Kirtland AFB, NM. The results indicate that near-IR photometric signatures can be used to distinguish among different satellite classes. Other uses of the data, e.g. anomaly resolution and health status, are discussed.
There are two main ways to mitigate the effects of atmospheric turbulence on an imaging system. A post factor approach, where data are opportunely acquired and processed in order to increase the overall resolution attainable by the optical system, speckle imaging is an example of such technique. The other approach is to use an adaptive optics system that will compensate for atmospheric effects before the data are recorded. Of course, the situation is not sharply distinct. Hybrid approaches have been proposed and demonstrated. Other approaches that are a mid-way between the two are also possible. The basic idea of static and dynamic pupil masking will be presented. Experimental results based on point sources and extended objects will be presented. Advantages and limitations of such technique will be discussed. Finally some new ideas involving fiber optics and liquid crystals will be presented.
In this paper we present a status report of our liquid crystal (LC) adaptive optics program. Liquid crystal have been proposed to be used for adaptive optics components by several authors. We are actively pursuing a two prong approach, on one side we have built a closed loop test bed based on a 127 element nematic LC device; on the other side we are actively involved in research on the ferroelectric side of the LC devices. In this paper we present preliminary results from our testbed. The essential elements of this testbed are a Shack-Hartman based wavefront sensors with an analog reconstructor, and the 127 nematic elements from Meadowlark Optics. Some of the basic experimental parameters will be reviewed, and result will be discussed. Furthermore we will present the status of our activity in the field of ferroelectric LC. Several prototypes are under testing to establish their capabilities as AO components.
The application of stellar interferometry to the observation of laser illuminated artificial satellites is investigated for a relocatable imaging system. Because of the satellite surface roughness, the light scattered from the surface can be considered spatially incoherent, creating laser speckle at the pupil of the array. The speckle noise is manifested in loss of fringe constrast because of the intensity distribution of speckle is predominately dark for aperture areas small compared to the characteristic speckle dimension. Speckle mitigation by use of aperture diameters larger that the speckle size result, on average, in fringe visibility errors because each aperture resolves the satellite. We quantify these effects in terms of incoherent imaging theory and discuss situations where speckle can be mitigated by the motion of the satellite. A conceptual design of a relocatable interferometer is shown with results of simulations which exclude the effects of the atmosphere.
Imaging array interferometry in the optical regime offers the promise of observing faint sources of small angular extent. A ground based system, however, must ameliorate the effects of atmospheric turbulence to maintain the very high resolution imaging capabilities of the instrument. Observing these interesting sources will require large diameter collectors with partial wavefront compensation. We highlight the mathematical treatment expressing the ensemble average image spectrum for the image plane and pupil plane interferometers. The theory treats aperture co-phasing and wavefront compensation by the idealized removal of an arbitrary number of Zernike modes.
KEYWORDS: Interferometers, Fourier transforms, Telescopes, Optical transfer functions, Deconvolution, Synthetic apertures, Astronomy, Receivers, Spatial frequencies, Signal to noise ratio
We present computer simulations of variable baseline 2D imaging optical interferometers operating at visible and infrared wavelengths. Sparse apertures of fewer than 10 receivers, baselines up to 400 m and aperture size from 1 to 2 m are considered. SNR limitations pose significant problems with dilute apertures observing faint sources; we explore various ways to address this problem. We simulate pupil plane visibility measurements under perfect conditions and in the presence of wavefront aberrations due to atmospheric distortion. A variety of ideal sources are studied, including stellar photospheres with features and artificial satellites. Earth rotation aperture synthesis over extended periods improves spatial frequency coverage of astronomical sources, while observation at multiple wavelengths improves coverage for geosynchronous satellites. We introduce a hybrid technique for performing a fast analytic pixel transform, similar to the fast discrete Fourier transform, which allows complex sources to be represented in pixel form but which admits the full floating point accuracy of analytic calculation. We study image deconvolution techniques to enhance the final image. An algorithm is presented for improvement of images formed from pupil plane interferometric data. Values are added to the frequency domain with the dominant constraint being an image taken with a small filled aperture instrument. A deconvolution technique using the entropy function is developed to enhance reconstruction of the truth image. Examples of image improvement obtained by the algorithm are presented.
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