Adaptive Optics Technology Research Articles

Effects of higher‐order wavefront aberrations on the eye's depth of focus

Abstract Purpose To evaluate the impact of higher order aberrations (HOA), defined by individual Zernike polynomial coefficients, on the eye's depth of focus using an adaptive optics (AO) system. Methods A crx1 AO visual simulator (Imagine Eyes, France) was used to introduce different amounts of individual 3rd and 4th order HOA in 10 healthy eyes. These HOA included coma (Z(3,‐1)) and trefoil (Z(3,‐3)) at magnitudes of +/‐0.3 µm, and spherical aberration (SA) (Z(4,0)) at magnitudes of +/‐0.3,+/‐0.6 and +/‐0.9 µm through a fixed 6‐mm pupil diameter. A through‐focus response (TFR) curve was assessed by recording the percentage of optotype letters of fixed 20/50 size that the subject could identify while these letters were presented at various target distances. Testing was performed under cycloplegia. For each applied HOA, the subject's depth of focus (DoF) and center of focus (CoF) were computed as, respectively, the half‐maximum width and the midpoint of the TFR curve. Results The introduction of SA resulted in linearly shifting the CoF by 1.3 D for each 0.5 µm of wavefront. The shift was hyperopic with positive SA, myopic with negative SA. The simulation of either positive or negative SA also had the effect of enhancing the DoF, up to a maximum increase of 2 D with 0.6 µm of SA. The enhancement became smaller when the SA was further increased. Trefoil and coma appeared to neither shift the CoF nor significantly modify the DoF. Conclusion AO technology allowed us to selectively test the visual impact of several HOA on the DoF. The introduction of SA significantly shifted and expanded the subjects’ overall DoF. This technique could help in designing optimal corrections for presbyopia and allowing patients to preview refractive surgery outcomes. Commercial interest

High resolution observations using adaptive optics: Achievements and future needs

Over the last few years, several interesting observations were obtained with the help of solar Adaptive Optics (AO). In this paper, few observations made using the solar AO are enlightened and briefly discussed. A list of disadvantages with the current AO system are presented. With telescopes larger than 1.5 m expected during the next decade, there is a need to develop the existing AO technologies for large aperture telescopes. Some aspects of this development are highlighted. Finally, the recent AO developments in India are also presented.

Calculations and Measurements of the Visual Benefit of Correcting the Higher-order Aberrations Using Adaptive Optics Technology

Purpose Our goal was to examine the accuracy of metrics, calculated using a numerical eye model including the measurement of the monochromatic aberrations of the eye, to predict the contrast sensitivity (CS) and visual acuity (VA) visual benefits (VB) of correcting higher-order aberrations (HO). Methods We measured, on the right eyes of 25 subjects (10 myopes and 15 emmetropes) aged 21 to 56 years, the 16 c/deg CS and high-contrast VA in two conditions of aberration corrections: (i) when correcting only the defocus and astigmatism terms and (ii) when dynamically correcting all the monochromatic aberration terms up to the 5 th order. The measured VB was defined as the ratio of the performances between these two conditions of aberration corrections. Results We measured a VB of 1.25 and 1.64 respectively in term of VA and CS. We did not find any influence of age on the VB and no statistical significant difference between the myopic and emmetropic group. The contrast sensitivity VB was well correlated (r 2=0.79) with the ratio of the modulation transfer functions calculated at 16 c/deg in both conditions of aberrations corrections (i.e. MTF 16c/deg HO/MTF 16c/deg SC). The levels of correlation between various metrics and measured visual acuity VB were lower (r 2=0.30 in the better case), however the averaged VB was correctly predicted by the ratio of the intersections between the MTF and a typically neural contrast threshold function. Conclusions Metrics based on wave aberration measurements are able to predict the impact of monochromatic aberrations on CS.

Effects of Zernike Wavefront Aberrations on Visual Acuity Measured Using Electromagnetic Adaptive Optics Technology

This study measured the changes in visual acuity induced by individual Zernike ocular aberrations of various root-mean-square (RMS) magnitudes. A crx1 Adaptive Optics Visual Simulator (Imagine Eyes) was used to modify the wavefront aberrations in nine eyes. After measuring ocular aberrations, the device was programmed to compensate for the eye's wavefront error up to the 4th order and successively apply different individual Zernike aberrations using a 5-mm pupil. The generated aberrations included defocus, astigmatism, coma, trefoil, and spherical aberration at a level of 0.1, 0.3, and 0.9 microm. Monocular visual acuity was assessed using computer-generated Landolt-C optotypes. Correction of the patients' aberrations improved visual acuity by a mean of 1 line (-0.1 logMAR) compared to best sphero-cylinder correction. Aberrations of 0.1 microm RMS resulted in a limited decrease in visual acuity (mean +0.05 logMAR), whereas aberrations of 0.3 microm RMS induced significant visual acuity losses with a mean reduction of 1.5 lines (+0.15 logMAR). Larger aberrations of 0.9 microm RMS resulted in greater visual acuity losses that were more pronounced with spherical aberration (+0.64 logMAR) and defocus (+0.62 logMAR), whereas trefoil (+0.22 logMAR) was found to be better tolerated. The electromagnetic adaptive optics visual simulator effectively corrected and generated wavefront aberrations up to the 4th order. Custom wavefront correction significantly improved visual acuity compared to best-spectacle correction. Symmetric aberrations (eg, defocus and spherical aberration) were more detrimental to visual performance.

Adaptive optics in microscopy

The imaging properties of optical microscopes are often compromised by aberrations that reduce image resolution and contrast. Adaptive optics technology has been employed in various systems to correct these aberrations and restore performance. This has required various departures from the traditional adaptive optics schemes that are used in astronomy. This review discusses the sources of aberrations, their effects and their correction with adaptive optics, particularly in confocal and two-photon microscopes. Different methods of wavefront sensing, indirect aberration measurement and aberration correction devices are discussed. Applications of adaptive optics in the related areas of optical data storage, optical tweezers and micro/nanofabrication are also reviewed.

Applications of adaptive‐optics in ophthalmology

Abstract Purpose: This presentation reviews the current and potential applications of adaptive optics (AO) in the area of ophthalmology. Methods: AO was invented by astrophysicists in order to eliminate image blur and twinkling in large terrestrial telescopes. This technique cancels the optical distortions that are introduced by the earth atmosphere, a turbid and inhomogeneous medium, in the light emitted by distant stars. Like the atmosphere, the human eye is optically imperfect: it suffers from wavefront aberrations whose pattern and amount differ between individuals. This is the reason why AO has met several applications in ophthalmology. One part of the AO technology consists in measuring the distortions of light using a wavefront sensor: this technique has been integrated into wavefront aberrometers that routinely improve the precision of LASIK procedures. Results: The full implementation of AO has recently led to other breakthrough devices. AO visual simulators are enhanced aberrometers that allow patients to visualize, at the pre‐operative stage, the expected outcome of refractive surgery procedures, including presbyopic ablations. Several research laboratories have implemented AO to improve the resolution of various retinal imaging techniques (fundus camera, SLO, OCT) up to the scale of single retinal cells. Three‐dimensional images of cone photoreceptors have recently been obtained with a resolution of 3μm, both in the longitudinal and transverse dimensions of the retinal tissue. Aside from this world‐record, the presentation will also address the limitations of the technique and describe some of the work in progress towards the clinical applications of AO technology. Conclusions: AO technology will likely provide new devices that meet unsatisfied needs in refractive surgery and retinal disagnostics.

Locating the Two Black Holes in NGC 6240

Mergers play an important role in galaxy evolution and are key to understanding the correlation between central-black hole mass and host-galaxy properties. We used the new technology of adaptive optics at the Keck II telescope to observe NGC 6240, a merger between two disk galaxies. Our high-resolution near-infrared images, combined with radio and x-ray positions, revealed the location and environment of two central supermassive black holes. Each is at the center of a rotating stellar disk, surrounded by a cloud of young star clusters. The brightest of these young clusters lie in the plane of each disk, but surprisingly are seen only on the disks' receding side.

Comparative Lyot Coronagraphy with Extreme Adaptive Optics Systems

As adaptive optics technology continues to improve, the stellar coronagraph will play an ever increasing role in ground-based high-contrast imaging observations. Although several different image masks exist for the most common type of coronagraph, the Lyot coronagraph, it is not yet clear what level of wave front correction must be reached in order to gain, either in starlight suppression or observing efficiency, by implementing a more sophisticated design. In this paper, we model image plane Lyot-style coronagraphs and test their response to a range of wave front correction levels, in order to identify regimes of atmospheric compensation where the use of hard-edge, Gaussian, and band-limited image masks becomes observationally advantageous. To delineate performances, we calculate the speckle noise floor mean intensity. We find that apodized masks provide little improvement over hard-edge masks until on-sky Strehl ratios exceed ~0.88Sqs, where Sqs is the intrinsic Strehl ratio provided by the optical system. Above this value, fourth-order band-limited masks outperform Gaussian masks by generating comparable contrast with higher Lyot stop throughput. Below this level of correction, hard-edge masks may be preferentially chosen, since they are less susceptible to low-order aberration content. The use of higher order band-limited masks is relegated to situations where quasi-static residual starlight cannot be sufficiently removed from the search area with speckle-nulling hardware.

Modelling the application of adaptive optics to wide‐field microscope live imaging

Wide-field fluorescence microscopy is an essential tool in modern cell biology. Unfortunately the image quality of fluorescence microscopes is often significantly degraded due to aberrations that occur under normal imaging conditions. In this article, we examine the use of adaptive optics technology to dynamically correct these problems to achieve close to ideal diffraction limited performance. Simultaneously, this technology also allows ultra-rapid focusing without having to move either the stage or the objective lens. We perform optical simulations to demonstrate the degree of correction that can be achieved.

Research on the Phase Aberration Correction with a Deformable Mirror Controlled by a Genetic Algorithm

In order to improve laser beam quality, a real number encoding genetic algorithm based on adaptive optics technology was presented. This algorithm was applied to control a 19-channel deformable mirror to correct phase aberration in laser beam. It is known that when traditional adaptive optics system is used to correct laser beam wave-front phase aberration, a precondition is to measure the phase aberration information in the laser beam. However, using genetic algorithms, there is no necessary to know the phase aberration information in the laser beam beforehand. The only parameter need to know is the Light intensity behind the pinhole on the focal plane. This parameter was used as the fitness function for the genetic algorithm. Simulation results show that the optimal shape of the 19-channel deformable mirror applied to correct the phase aberration can be ascertained. The peak light intensity was improved by a factor of 21, and the encircled energy strehl ratio was increased to 0.34 from 0.02 as the phase aberration was corrected with this technique.

Adaptive Optics Ophthalmoscopy: Results and Applications

The living human eye's optical aberrations set a limit to retinal imaging in the clinical setting. Progress in the field of adaptive optics has offered unique solutions to this problem. The purpose of this review is to summarize the most recent advances in adaptive optics ophthalmoscopy. Adaptive optics technology has been combined with flood illumination imaging, confocal scanning laser ophthalmoscopy, and optical coherence tomography for the high resolution imaging of the retina. The advent of adaptive optics technology has provided the technical platform for the compensation of the eye's aberration and made possible the observation of single cones, small capillaries, nerve fibers, and leukocyte dynamics as well as the ultrastructure of the optic nerve head lamina cribrosa in vivo. Detailed imaging of retinal infrastructure provides valuable information for the study of retinal physiology and pathology.

Detection and computation of the amount of atmospheric wave-front tilt in the application of adaptive optics technology to lunar laser ranging

For dealing with the problem of too few photons in the return wave in lunar laser ranging, the effect of the atmospheric turbulence is studied. The principles of the two tracking algorithms, cross correlation and absolute difference are studied and programs are written, which are tested with solar data. Collected image data of the interested area on the lunar disc are given. The integrated tilt signals of the atmospheric wave front obtained are treated by different methods under different conditions and the algorithms are compared as to their effectiveness.

Characterizing the Adaptive Optics Off‐Axis Point‐Spread Function. I. A Semiempirical Method for Use in Natural Guide Star Observations1,1Based, in part, on observations obtained at the Lick Observatory, which is operated by the University of California. 22All authors except D. C. are affiliated with the Center for Adaptive Optics.

ABSTRACTEven though the technology of adaptive optics (AO) is rapidly maturing, calibration of the resulting images remains a major challenge. The AO point‐spread function (PSF) changes quickly in both time and position on the sky. In a typical observation, the star used for guiding will be separated from the scientific target by 10″–30″. This is sufficient separation to render images of the guide star by themselves nearly useless in characterizing the PSF at the off‐axis target position. A semiempirical technique is described that improves the determination of the AO off‐axis PSF. The method uses calibration images of dense star fields to determine the change in PSF with field position. It then uses this information to correct contemporaneous images of the guide star to produce a PSF that is more accurate for both the target position and the time of a scientific observation. We report on tests of the method using natural guide star AO systems on the Canada‐France‐Hawaii Telescope and Lick Observatory Shane Telescope, augmented by simple atmospheric computer simulations. At 25″ off‐axis, predicting the PSF FWHM using only information about the guide star results in an error of 60%. Using an image of a dense star field lowers this error to 33%, and our method, which also folds in information about the on‐axis PSF, further decreases the error to 19%.

Spatial optical (2+1)-dimensional scalar- and vector-solitons in saturable nonlinear media

(2+1)-dimensional optical spatial solitons have become a major field of research in nonlinear physics throughout the last decade due to their potential in adaptive optical communication technologies. With the help of photorefractive crystals that supply the required type of nonlinearity for soliton generation, we are able to demonstrate experimentally the formation, the dynamic properties, and especially the interaction of solitary waves, which were so far only known from general soliton theory. Among the complex interaction scenarios of scalar solitons, we reveal a distinct behavior denoted as anomalous interaction, which is unique in soliton-supporting systems. Further on, we realize highly parallel, light-induced waveguide configurations based on photorefractive screening solitons that give rise to technical applications towards waveguide couplers and dividers as well as all-optical information processing devices where light is controlled by light itself. Finally, we demonstrate the generation, stability and propagation dynamics of multi-component or vector solitons, multipole transverse optical structures bearing a complex geometry. In analogy to the particle-light dualism of scalar solitons, various types of vector solitons can - in a broader sense - be interpreted as molecules of light.

Spatial optical (2+1)‐dimensional scalar‐ and vector‐solitons in saturable nonlinear media

Abstract(2+1)‐dimensional optical spatial solitons have become a major field of research in nonlinear physics throughout the last decade due to their potential in adaptive optical communication technologies. With the help of photorefractive crystals that supply the required type of nonlinearity for soliton generation, we are able to demonstrate experimentally the formation, the dynamic properties, and especially the interaction of solitary waves, which were so far only known from general soliton theory. Among the complex interaction scenarios of scalar solitons, we reveal a distinct behavior denoted as anomalous interaction, which is unique in soliton‐supporting systems. Further on, we realize highly parallel, light‐induced waveguide configurations based on photorefractive screening solitons that give rise to technical applications towards waveguide couplers and dividers as well as all‐optical information processing devices where light is controlled by light itself. Finally, we demonstrate the generation, stability and propagation dynamics of multi‐component or vector solitons, multipole transverse optical structures bearing a complex geometry. In analogy to the particle‐light dualism of scalar solitons, various types of vector solitons can ‐ in a broader sense ‐ be interpreted as molecules of light.

A “Silicon Eye” Using Mems Micromirrors

The U.S. Air Force Research Laboratory's (AFRL) aggressive pursuit of reducing the size and weight of satellite systems for advanced space missions is providing a vital thrust to the development of “systemson-a-chip.” Adaptive optics technologies offer tremendous potential in reducing the weight and cost of space-based optical systems.

Optical Metrology of Adaptive Membrane Mirrors

Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight increases the cost and decreases the selection of launch vehicles. The challenge of membrane optics in space is implementing adaptive optics technology via a membrane surface that provides at least rough order of magnitude imaging—enabling a large lightweight imaging system where small can be eliminated by processes such as real time holography. A system was developed which categorizes surface properties of optical quality membrane material with the ability to interpret membrane mirror deformation. Membrane mirrors with adaptive control were constructed and analyzed using this system which provided sub-micron deformation data with associated optical aberrations, proving the ability of PVDF film to provide adaptive control to regions of interest on membrane mirrors. Remaining technical challenges include bonding methods and eventual multi-layer laminate bonding of the PVDF control surfaces to the membrane.

Adaptive optics ophthalmoscopy.

Retinal images in the human eye are normally degraded because we are forced to use the optical system of the human eye--which is fraught with aberrations--as the objective lens. The recent application of adaptive optics technology to measure and compensate for these aberrations has produced retinal images in human eyes with unprecedented resolution. The adaptive optics ophthalmoscope is used to take pictures of photoreceptors and capillaries and to study spectral and angular tuning properties of individual photoreceptors. Application of adaptive optics technology for ophthalmoscopy promises continued progress toward understanding the basic properties of the living human retina and also for clinical applications.

Making Light Work

Windows or eyeglasses that darken in bright light are examples of nonlinear optical materials, in which the response of the medium, in this case the refractive index, changes dramatically with the light intensity. However, the response time, typically seconds, of these materials is too slow to be of practical use for electro-optic or all-optical switching processes. The combination of intense coherent radiation available from lasers together with newly developed photorefractive materials is providing nonlinear optical response times on ultrafast time scales. Such systems allow photons to be added, subtracted, mixed, and manipulated in ways impossible in our familiar low-light-intensity environment. The Reviews in this special issue of Science look at some of those developments in the field of nonlinear optics and the applications they are finding. To study the dynamics of an event too fast for our eyes to see, snapshots of the event are taken, pieced together, and then played back in slow motion. Cameras equipped with fast mechanical shutters allow us to view microsecond snippets of time. The detailed dynamics of chemical reactions or of electronic transitions in crystalline materials can be revealed in a similar manner by following processes with laser pulses on time scales of picoseconds (10−12 s) or femtoseconds (10−15 s). Steinmeyer et al. (p. [1507][1]) review the role of nonlinear optics in the generation of ultrafast laser pulses and focus on the role being played by direct laser oscillators. It is necessary in spectroscopy to tune in to the energy scale that is relevant to the particular system under study. However, lasers generally emit light at very precise and fixed wavelengths. Dunn and Ebrahimzadeh (p. [1513][2]) describe how high-quality monochromatic light can be generated with optical parametric oscillators in which the interaction between photons can be controlled. This approach achieves a flexibility in generating the output light that is not available to conventional lasers. The past decade has seen an explosion in communication technology. The continuing challenge is to transfer ever-larger amounts of information from one point to another at as high a rate as possible without losing any data in the process. One proposal to overcome the transfer rate limitation of semiconductors is to use all-optical networks. Today, thousands of kilometers of optical fibers encircle the globe. As more information is transferred down a fiber, however, nonlinearities become important and can actually limit the information capacity. As a light pulse propagates through a medium, it disperses or broadens, and repeater stations are needed periodically to prevent pulses from smearing into one another. However, with sufficiently high light intensity, the refractive index of the medium is locally increased and the light is confined to that region by total internal reflection. The light then traverses the medium without loss of intensity and is described as a spatial soliton. Stegeman and Segev (p. [1518][3]) review how such nonlinearities can be used to advantage in the generation and interaction of solitons in their role as information carriers, and Cotter et al. (p. [1523][4]) review the techniques required to implement processing of the optical signals at transfer rates in excess of 100 gigabits per second. A News story (p. [1502][5]) examines the promise of storing such torrents of data in holograms: durable optical inscriptions written in nonlinear optical materials. And two other News stories (pp. [1500][6] and [1504][7]) describe progress in other fields of optics: latticelike photonic crystals, which can trap or channel light; and adaptive optics technology, which helps telescopes undo the effects of atmospheric turbulence. [1]: /lookup/doi/10.1126/science.286.5444.1507 [2]: /lookup/doi/10.1126/science.286.5444.1513 [3]: /lookup/doi/10.1126/science.286.5444.1518 [4]: /lookup/doi/10.1126/science.286.5444.1523 [5]: /lookup/doi/10.1126/science.286.5444.1502 [6]: /lookup/doi/10.1126/science.286.5444.1500 [7]: /lookup/doi/10.1126/science.286.5444.1504

On the Topical Papers of Adaptive Optics and Phase Conjugation Technologies

On the Topical Papers of Adaptive Optics and Phase Conjugation Technologies