Showing papers on "Wavefront published in 2006"

Adaptive wavefront correction in two-photon microscopy using coherence-gated wavefront sensing

Abstract: The image quality of a two-photon microscope is often degraded by wavefront aberrations induced by the specimen. We demonstrate here that resolution and signal size in two-photon microcopy can be substantially improved, even in living biological specimens, by adaptive wavefront correction based on sensing the wavefront of coherence-gated backscattered light (coherence-gated wavefront sensing, CGWS) and wavefront control by a deformable mirror. A nearly diffraction-limited focus can be restored even for strong aberrations. CGWS-based wavefront correction should be applicable to samples with a wide range of scattering properties and it should be possible to perform real-time pixel-by-pixel correction even at fast scan speeds.

Numerical parametric lens for shifting, magnification, and complete aberration compensation in digital holographic microscopy

Abstract: The concept of numerical parametric lenses (NPL) is introduced to achieve wavefront reconstruction in digital holography. It is shown that operations usually performed by optical components and described in ray geometrical optics, such as image shifting, magnification, and especially complete aberration compensation (phase aberrations and image distortion), can be mimicked by numerical computation of a NPL. Furthermore, we demonstrate that automatic one-dimensional or two-dimensional fitting procedures allow adjustment of the NPL parameters as expressed in terms of standard or Zernike polynomial coefficients. These coefficients can provide a quantitative evaluation of the aberrations generated by the specimen. Demonstration is given of the reconstruction of the topology of a microlens.

High-Contrast Imaging from Space: Speckle Nulling in a Low-Aberration Regime

Abstract: High-contrast imaging from space must overcome two major noise sources to successfully detect a terrestrial planet angularly close to its parent star: photon noise from diffracted starlight and speckle noise from starlight scattered by instrumentally generated wave front perturbation. Coronagraphs tackle only the photon noise contribution by reducing diffracted starlight at the location of a planet. Speckle noise should be addressed with adaptive optics systems. Following the tracks of Malbet, Yu, and Shao, we develop in this paper two analytical methods for wave front sensing and control that aims at creating "dark holes," i.e., areas of the image plane cleared of speckles, assuming an ideal coronagraph and small aberrations. The first method, "speckle field nulling," is a fast FFT-based algorithm that requires the deformable-mirror influence functions to have identical shapes. The second method, "speckle energy minimization," is more general and provides the optimal deformable mirror shape via matrix inversion. With an N × N deformable mirror, the size of the matrix to be inverted is either N2 × N2 in the general case or only N × N if the influence functions can be written as the tensor product of two one-dimensional functions. Moreover, speckle energy minimization makes it possible to trade off some of the dark hole area against an improved contrast. For both methods, complex wave front aberrations (amplitude and phase) are measured using just three images taken with the science camera (no dedicated wave front sensing channel is used); therefore, there are no noncommon path errors. We assess the theoretical performance of both methods with numerical simulations including realistic speckle noise and experimental influence functions. We find that these speckle-nulling techniques should be able to improve the contrast by several orders of magnitude.

Pancharatnam-Berry phase optical elements for wave front shaping in the visible domain: Switchable helical mode generation

Abstract: We report the realization of a Pancharatnam-Berry phase optical element [Z. Bomzon, G. Biener, V. Kleiner, and E. Hasman, Opt. Lett. 27, 1141 (2002)], for wave front shaping working in the visible spectral domain, based on patterned liquid crystal technology. This device generates helical modes of visible light with the possibility of electro-optically switching between opposite helicities by controlling the handedness of the input circular polarization. By cascading this approach, fast switching among multiple wave front helicities can be achieved, with potential applications to multistate optical information encoding. The approach demonstrated here can be generalized to other polarization-controlled devices for wave front shaping, such as switchable lenses, beam splitters, and holographic elements.

Holographic optical trapping

Abstract: Holographic optical tweezers use computer-generated holograms to create arbitrary three-dimensional configurations of single-beam optical traps that are useful for capturing, moving, and transforming mesoscopic objects. Through a combination of beam-splitting, mode-forming, and adaptive wavefront correction, holographic traps can exert precisely specified and characterized forces and torques on objects ranging in size from a few nanometers to hundreds of micrometers. Offering nanometer-scale spatial resolution and real-time reconfigurability, holographic optical traps provide unsurpassed access to the microscopic world and have found applications in fundamental research, manufacturing, and materials processing.

Comparison of the retinal image quality with a Hartmann-Shack wavefront sensor and a double-pass instrument.

Abstract: Purpose Wavefront sensors provide quite useful information on the optical quality of the eye. However, in eyes where very high-order aberrations and scattered light are prominent, wavefront sensors may overestimate retinal image quality. This study showed that, in those cases, the double-pass technique is a complementary tool for better estimation of ocular optical quality. Methods A double-pass (DP) instrument was used, based on recording images of a point source in near-infrared light after reflection in the retina and double-pass through the ocular media. The aberrations were also measured with a prototype of near-infrared Hartmann-Shack (HS) wavefront sensor adapted to the clinical environment. From the wave aberrations, the modulation transfer function (MTF) was calculated (MTF_HS). The MTF was also obtained from the double-pass images (MTF_DP). Both techniques were applied in normal young subjects as the control and in three other groups of eyes: older subjects, after LASIK refractive surgery, and after IOL implantation. Results The MTFs obtained from DP and HS techniques were compared. In the group of normal eyes with low levels of intraocular scattering, these estimates were quite similar, indicating that both techniques captured well most of the optical degradation. However, in eyes where scatter was more predominant (e.g., early cataract, posterior capsular opacification after IOL implantation) the MTF provided by the HS sensor was always higher than the MTF obtained from DP. A single parameter was used to indicate the differences. Conclusions In eyes with low scattering, DP and HS techniques provided similar estimates of the retinal image quality. However, in a patient's eye with mild to severe amount of scatter, wavefront sensors might overestimate image quality, whereas the DP technique produces a more accurate description of the optical quality, better correlated with the quality of vision.

High-speed digital holographic interferometry for vibration measurement

Abstract: A system based on digital holographic interferometry for the measurement of vibrations is presented. A high-power continuous laser (10 W) and a high-speed CCD camera are used. Hundreds of holograms of an object that has been subjected to dynamic deformation are recorded. The acquisition speed and the time of exposure of the detector are determined by the vibration frequency. Two methods are presented for triggering the camera in order to acquire at a given phase of the vibration. The phase of the wavefront is calculated from the recorded holograms by use of a two-dimensional digital Fourier-transform method. The deformation of the object is obtained from the phase. By combination of the deformations recorded at different times it is possible to reconstruct the vibration of the object.

Complete wavefront reconstruction using sequential intensity measurements of a volume speckle field

Abstract: The recording of the volume speckle field from an object at different planes combined with the wave propagation equation allows the reconstruction of the wavefront phase and amplitude without requiring a reference wave. The main advantage of this single-beam multiple-intensity reconstruction (SBMIR) technique is the simple experimental setup because no reference wave is required as in the case of holography. The phase retrieval technique is applied to the investigation of diffusely transmitting and reflecting objects. The effects of different parameters on the quality of reconstructions are investigated by simulation and experiment. Significant enhancements of the reconstructions are observed when the number of intensity measurements is 15 or more and the sequential measurement distance is 0.5 mm or larger. Performing two iterations during the reconstruction process using the calculated phase also leads to better reconstruction. The results from computer simulations confirm the experiments. Analysis of transverse and longitudinal intensity distributions of a volume speckle field for the SBMIR technique is presented. Enhancing the resolution method by shifting the camera a distance of a half-pixel in the lateral direction improves the sampling of speckle patterns and leads to better quality reconstructions. This allows the possibility of recording wave fields from larger test objects.

Coherent combination of high-power, zigzag slab lasers.

Abstract: We demonstrate a scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains. A common master oscillator injects a sequence of multikilowatt Nd:YAG zigzag slab amplifiers. Adaptive optics correct the wavefront of each amplified beamlet. The beamlets are tiled side by side and actively phase locked to form a single output beam. The laser produces 19 kW with beam quality <2x diffraction limited. To the best of our knowledge, this is the brightest cw solid-state laser demonstrated to date.

Wave front sensor-less adaptive optics: a model-based approach using sphere packings

Abstract: Certain adaptive optics systems do not employ a wave front sensor but rather maximise a photodetector signal by appropriate control of an adaptive element. The maximisation procedure must be optimised if the system is to work efficiently. Such optimisation is often implemented empirically, but further insight can be obtained by using an appropriate mathematical model. In many practical systems aberrations can be accurately represented by a small number of modes of an orthogonal basis, such as the Zernike polynomials. By heuristic reasoning we develop a model for the operation of such systems and demonstrate a link with the geometrical problems of sphere packings and coverings. This approach aids the optimisation of control algorithms and is illustrated by application to direct search and hill climbing algorithms. We develop an efficient scheme using a direct maximisation calculation that permits the measurement of N Zernike modes with only N +1 intensity measurements.

Quantitative phase-contrast microscopy by a lateral shear approach to digital holographic image reconstruction.

Abstract: Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.

Adaptive Optics for Vision Science: Principles, Practices, Design, and Applications

Abstract: FOREWORD. ACKNOWLEDGMENTS. CONTRIBUTORS. PART ONE: INTRODUCTION. 1. Development of Adaptive Optics in Vision Science and Ophthalmology (David R. Williams and Jason Porter). 1.1 Brief History of Aberration Correction in the Human Eye. 1.2 Applications of Ocular Adaptive Optics. PART TWO: WAVEFRONT MEASUREMENT AND CORRECTION. 2. Aberration Structure of the Human Eye (Pablo Artal, Juan M. Bueno, Antonio Guirao, and Pedro M. Prieto). 2.1 Introduction. 2.2 Location of Monochromatic Aberrations Within the Eye. 2.3 Temporal Properties of Aberrations: Accommodation and Aging. 2.4 Chromatic Aberrations. 2.5 Off-Axis Aberrations. 2.6 Statistics of Aberrations in Normal Populations. 2.7 Effects of Polarization and Scatter. 3. Wavefront Sensing and Diagnostic Uses (Geunyoung Yoon). 3.1 Wavefront Sensors for the Eye. 3.2 Optimizing a Shack-Hartmann Wavefront Sensor. 3.3 Calibration of a Wavefront Sensor. 3.4 Summary. 4. Wavefront Correctors for Vision Science (Nathan Doble and Donald T. Miller). 4.1 Introduction. 4.2 Principal Components of an AO System. 4.3 Wavefront Correctors. 4.4 Wavefront Correctors Used in Vision Science. 4.5 Performance Predictions for Various Types of Wavefront Correctors. 4.6 Summary and Conclusion. 5. Control Algorithms (Li Chen). 5.1 Introduction. 5.2 Confi guration of Lenslets and Actuators. 5.3 Infl uence Function Measurement. 5.4 Spatial Control Command of the Wavefront Corrector. 5.5 Temporal Control Command of the Wavefront Corrector. 6. Adaptive Optics Software for Vision Research (Ben Singer). 6.1 Introduction. 6.3 Measuring Wavefront Slope. 6.4 Aberration Recovery. 6.5 Correcting Aberrations. 6.6 Application-Dependent Considerations. 6.7 Conclusion. 7. Adaptive Optics System Assembly and Integration (Brian J. Bauman and Stephen K. Eisenbies). 7.1 Introduction. 7.2 First-Order Optics of the AO System. 7.3 Optical Alignment. 7.4 AO System Integration. 8. System Performance Characterization (Marcos A. van Dam). 8.1 Introduction. 8.2 Strehl Ratio. 8.3 Calibration Error. 8.4 Fitting Error. 8.5 Measurement and Bandwidth Error. 8.6 Addition of Wavefront Error Terms. PART THREE: RETINAL IMAGING APPLICATIONS. 9. Fundamental Properties of the Retina (Ann E. Elsner). 9.1 Shape of the Retina. 9.2 Two Blood Supplies. 9.3 Layers of the Fundus. 9.4 Spectra. 9.5 Light Scattering. 9.6 Polarization. 9.7 Contrast from Directly Backscattered or Multiply Scattered Light. 9.8 Summary. 10. Strategies for High-Resolution Retinal Imaging (Austin Roorda, Donald T. Miller, and Julian Christou). 10.1 Introduction. 10.2 Conventional Imaging. 10.3 Scanning Laser Imaging. 10.4 OCT Ophthalmoscope. 10.5 Common Issues for all AO Imaging Systems. 10.6 Image Postprocessing. PART FOUR: VISION CORRECTION APPLICATIONS. 11. Customized Vision Correction Devices (Ian Cox). 11.1 Contact Lenses. 11.2 Intraocular Lenses. 12. Customized Corneal Ablation (Scott M. MacRae). 12.1 Introduction. 12.2 Basics of Laser Refractive Surgery. 12.3 Forms of Customization. 12.4 The Excimer Laser Treatment. 12.5 Biomechanics and Variable Ablation Rate. 12.6 Effect of the LASIK Flap. 12.7 Wavefront Technology and Higher Order Aberration Correction. 12.8 Clinical Results of Excimer Laser Ablation. 12.9 Summary. 13. From Wavefronts To Refractions (Larry N. Thibos). 13.1 Basic Terminology. 13.2 Goal of Refraction. 13.3 Methods for Estimating the Monochromatic Refraction from an Aberration Map. 13.4 Ocular Chromatic Aberration and the Polychromatic Refraction. 13.5 Experimental Evaluation of Proposed Refraction Methods. 14. Visual Psychophysics With Adaptive Optics (Joseph L. Hardy, Peter B. Delahunt, and John S. Werner). 14.1 Psychophysical Functions. 14.2 Psychophysical Methods. 14.3 Generating the Visual Stimulus. 14.4 Conclusions. PART FIVE: DESIGN EXAMPLES. 15. Rochester Adaptive Optics Ophthalmoscope (Heidi Hofer, Jason Porter, Geunyoung Yoon, Li Chen, Ben Singer, and David R. Williams) 15.1 Introduction. 15.2 Optical Layout. 15.3 Control Algorithm. 15.4 Wavefront Correction Performance. 15.5 Improvement in Retinal Image Quality. 15.6 Improvement in Visual Performance. 15.7 Current System Limitations. 15.8 Conclusion. 16. Design of an Adaptive Optics Scanning Laser Ophthalmoscope (Krishnakumar Venkateswaran, Fernando Romero-Borja, and Austin Roorda). 16.1 Introduction. 16.2 Light Delivery. 16.3 Raster Scanning. 16.4 Adaptive Optics in the SLO. 16.5 Optical Layout for the AOSLO. 16.6 Image Acquisition. 16.7 Software Interface for the AOSLO. 16.8 Calibration and Testing. 16.9 AO Performance Results. 16.10 Imaging Results. 16.11 Discussions on Improving Performance of the AOSLO. 17. Indiana University AO-OCT System (Yan Zhang, Jungtae Rha, Ravi S. Jonnal, and Donald T. Miller). 17.1 Introduction. 17.2 Description of the System. 17.3 Experimental Procedures. 17.4 AO Performance. 17.5 Example Results with AO Conventional Flood- Illuminated Imaging. 17.6 Example Results With AO Parallel SD-OCT Imaging. 17.7 Conclusion. 18. Design and Testing of A Liquid Crystal Adaptive OpticsPhoropter (Abdul Awwal and Scot Olivier). 18.1 Introduction. 18.2 Wavefront Sensor Selection. 18.3 Beacon Selection: Size and Power, SLD versus Laser Diode. 18.4 Wavefront Corrector Selection. 18.5 Wavefront Reconstruction and Control. 18.6 Software Interface. 18.7 AO Assembly, Integration, and Troubleshooting. 18.8 System Performance, Testing Procedures, and Calibration. 18.9 Results from Human Subjects. 18.10 Discussion. 18.11 Summary. APPENDIX A: OPTICAL SOCIETY OF AMERICA'S STANDARDS FOR REPORTING OPTICAL ABERRATIONS. GLOSSARY. SYMBOL TABLE. INDEX.

A microwave channelizer and spectroscope based on an integrated optical Bragg-grating Fabry-Perot and integrated hybrid Fresnel lens system

Abstract: A compact means to separate microwave and millimeter-wave optical signals by RF frequency in real time is demonstrated. The approach is to employ an integrated optical Bragg grating Fabry-Perot (BGFP) device to spatially separate optically modulated microwave signals with high resolution. The compactness is achieved through the use of an integrated optical hybrid diffractive lens beam expander to provide the required optical wavefront to the BGFP. A proof-of-principle measurement was performed from 1 to 23 GHz with peak finesse of 27. The theoretical analysis, fabrication procedure, experimental results, limitations, and improvements are described.

Predicting the Optical Performance of Eyes Implanted with IOLs to Correct Spherical Aberration

Abstract: Purpose To use powerful modeling techniques for predicting the optical performance of eyes implanted with different types of intraocular lenses (IOLs). This approach will allow performance of "virtual cataract surgery," with different IOL designs that can be used and physical parameters that may occur during actual surgery-in particular, in IOLs that correct spherical aberration. Methods A computer model was developed to predict the optical performance of individual eyes after IOL implantation. The approach was validated in a group of patients with eyes implanted with different IOLs. In these patients, corneal wavefront aberrations were calculated from elevations provided by videokeratography. Ocular aberrations were measured with a high-dynamic range Hartmann-Shack wavefront sensor. Misalignments (IOL tilt and decentration) were estimated with a new instrument, based on recording Purkinje images. This model of particular corneal aberrations and IOL parameters (intrinsic optical design details plus geometric location data) was used to estimate the total ocular aberrations after surgery and to compared them with actual aberrations measured directly with the wavefront sensor. Results The aberrations of implanted eyes predicted by the individualized optical models were well correlated with the actual aberration measured in each subject. This result indicates that the approach is adequate in evaluating the actual optical performance of different types of lenses. The model allows a large number of "virtual" surgeries to be performed, to test the performance of current or future IOL designs. Conclusions A "virtual surgery" approach was designed to predict the optical performance in pseudophakic eyes. In each subject, it was possible to obtain the eye's optical performance with a particular IOL and biometric data after surgery. Specifically, this modeling can be used to evaluate the tolerances to misalignments and depth of focus of IOLs correcting spherical aberration in actual eyes. This approach is quite powerful and is especially applicable to the study of current and future aberration-correction IOL designs.

Determination of the profile of atmospheric optical turbulence strength from SLODAR data

Abstract: Slope Detection and Ranging (SLODAR) is a technique for the measurement of the vertical profile of atmospheric optical turbulence strength. Its main applications are astronomical site characterization and real-time optimization of imaging with adaptive optical correction. The turbulence profile is recovered from the cross-covariance of the slope of the optical phase aberration for a double star source, measured at the telescope with a wavefront sensor (WFS). Here, we determine the theoretical response of a SLODAR system based on a Shack–Hartmann WFS to a thin turbulent layer at a given altitude, and also as a function of the spatial power spectral index of the optical phase aberrations. Recovery of the turbulence profile via fitting of these theoretical response functions is explored. The limiting resolution in altitude of the instrument and the statistical uncertainty of the measured profiles are discussed. We examine the measurement of the total integrated turbulence strength (the seeing) from the WFS data and, by subtraction, the fractional contribution from all turbulence above the maximum altitude for direct sensing of the instrument. We take into account the effects of noise in the measurement of wavefront slopes from centroids and the form of the spatial structure function of the atmospheric optical aberrations.

Phase retrieval algorithm for JWST Flight and Testbed Telescope

Abstract: An image-based wavefront sensing and control algorithm for the James Webb Space Telescope (JWST) is presented. The algorithm heritage is discussed in addition to implications for algorithm performance dictated by NASA's Technology Readiness Level (TRL) 6. The algorithm uses feedback through an adaptive diversity function to avoid the need for phase-unwrapping post-processing steps. Algorithm results are demonstrated using JWST Testbed Telescope (TBT) commissioning data and the accuracy is assessed by comparison with interferometer results on a multi-wave phase aberration. Strategies for minimizing aliasing artifacts in the recovered phase are presented and orthogonal basis functions are implemented for representing wavefronts in irregular hexagonal apertures. Algorithm implementation on a parallel cluster of high-speed digital signal processors (DSPs) is also discussed.

Adaptive optics enhanced simultaneous en-face optical coherence tomography and scanning laser ophthalmoscopy

Abstract: A novel combination of adaptive optics with a simultaneous en-face OCT/SLO system for high resolution imaging of the in-vivo human retina is presented. Pairs of retinal images are shown and performance of the system is evaluated with and without dynamic wavefront correction. The adaptive optics closed loop system operates at a frame rate of 9 Hz and incorporates a Shack-Hartmann wavefront sensor based on a highly sensitive Andor camera and a 37 actuator OKO membrane deformable mirror to correct for ocular aberrations. The system produces C-scan pairs of images at a frame rate of 2 Hz. The correction of aberrations produced by the adaptive optics closed-loop system increased the signal-to-noise ratio in images obtained from volunteer eyes by up to 6 dB in the OCT channel and up to 9 dB in the SLO channel. A slight improvement in the lateral resolution was also obtained, from 6.5 μm before to 5 μm after closing the adaptive optics loop.

Phase-shifting digital holography with a phase difference between orthogonal polarizations.

Abstract: Phase-shifting digital holography with a phase difference between orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with the distributions of a reference wave and an object wave, the complex field of the object's wavefront can be obtained. Preliminary experimental results are shown to confirm the proposed method.

Wave front sensing method and apparatus

Abstract: A new way of mixing instrumental and digital means is described for the general field of wave front sensing. The present invention describes the use, the definition and the utility of digital operators, called digital wave front operators (DWFO) or digital lenses (DL), specifically designed for the digital processing of wave fronts defined in amplitude and phase. DWFO are of particular interest for correcting undesired wave front deformations induced by instrumental defects or experimental errors. DWFO may be defined using a mathematical model, e.g. a polynomial function, which involves coefficients. The present invention describes automated and semi-automated procedures for calibrating or adjusting the values of these coefficients. These procedures are based on the fitting of mathematical models on reference data extracted from specific regions of a wave front called reference areas, which are characterized by the fact that specimen contributions are a priori known in reference areas. For example, reference areas can be defined in regions where flat surfaces of a specimen produce a constant phase function. The present invention describes also how DWFO can be defined by extracting reference data along one-dimensional (1D) profiles. DWFO can also be defined in order to obtain a flattened representation of non-flat area of a specimen. Several DWFO or DL can be combined, possibly in addition with procedures for calculating numerically the propagation of wave fronts. A DWFO may also be defined experimentally, e.g. by calibration procedures using reference specimens. A method for generating a DWFO by filtering in the Fourier plane is also described. All wave front sensing techniques may benefit from the present invention. The case of a wave front sensor based on digital holography, e.g. a digital holographic microscope (DHM), is described in more details. The use of DWFO improves the performance, in particular speed and precision, and the ease of use of instruments for wave front sensing. The use of DWFO results in instrumental simplifications, costs reductions, and enlarged the field of applications. The present invention defines a new technique for imaging and metrology with a large field of applications in material and life sciences, for research and industrial applications.

Optical vortex metrology based on the core structures of phase singularities in Laguerre-Gauss transform of a speckle pattern

Abstract: A new technique for displacement measurement is proposed that makes use of phase singularities in the complex signal generated by a Laguerre-Gauss filter operation applied to a speckle pattern. The core structures of phase singularities are used as unique fingerprints attached to the object surface, and the displacement is determined by tracing the movement of registered phase singularities with their correspondence being identified by the fingerprints. Experimental results for translational and rotational displacement measurements are presented that demonstrate large dynamic range and high spatial resolution of the proposed optical vortex metrology.

Reflectivity and optical surface height requirements in a broadband coronagraph. 1. Contrast floor due to controllable spatial frequencies.

Abstract: We derive the broadband contrast floor in a coronagraphic telescope having nonideal optical surfaces. We consider only fundamental spatial frequencies within the control bandwidth of the coronagraph's deformable mirror. Cross terms arising from the beating of spatial frequencies beyond the deformable mirror control bandwidth will be considered in a second paper. Two wavefront control systems are analyzed:a zero-path difference Michelson interferometer with two deformable mirrors at a pupil image, and a sequential pair of deformable mirrors with one placed at a pupil image. We derive requirements on optical surface figure and reflectivity uniformity for both cases.

Simulated annealing in ocular adaptive optics.

Abstract: We present what is to our knowledge a first hardware realization of a simulated annealing algorithm in an adaptive optics system designed to image the retina of the human eye. The algorithm is applied to the retinal image itself without the need for wavefront sensors in the system. We find that this optimization algorithm can be an alternative to the traditional Hartmann-Shack sensing. We also compare the simulated annealing algorithm to the stochastic parallel gradient descent algorithm.

Large-scale optical-field measurements with geometric fibre constructs.

Abstract: Optical fields are measured using sequential arrangements of optical components such as lenses, filters, and beam splitters in conjunction with planar arrays of point detectors placed on a common axis1. All such systems are constrained in terms of size, weight, durability and field of view. Here a new, geometric approach to optical-field measurements is presented that lifts some of the aforementioned limitations and, moreover, enables access to optical information on unprecedented length and volume scales. Tough polymeric photodetecting fibres drawn from a preform2 are woven into light-weight, low-optical-density, two- and three-dimensional constructs that measure the amplitude and phase of an electromagnetic field on very large areas. First, a three-dimensional spherical construct is used to measure the direction of illumination over 4π steradians. Second, an intensity distribution is measured by a planar array using a tomographic algorithm. Finally, both the amplitude and phase of an optical wave front are acquired with a dual-plane construct. Hence, the problem of optical-field measurement is transformed from one involving the choice and placement of lenses and detector arrays to that of designing geometrical constructions of polymeric, light-sensitive fibres.

Treatment of skin with acoustic energy

Abstract: Methods and apparatus (10) are disclosed for applying acoustic energy (21) to the skin (12) whereby the wavefront can be controlled to confine the focused energy to a desired subsurface region. Acoustic waveguides (26) are disclosed which compensate for distortions that otherwise occur when a focused acoustic beam crosses a boundary, such as the transition from a treatment device to a target region of skin. The invention is especially useful with devices that focus ultrasound energy by condensing a propagating wavefront . The invention compensates for the mismatch in acoustic properties of the device's waveguide and the biological tissue that typically cause portions of the collapsing wavefront to lag behind other portions and, thereby, limit the focusing capabilities of acoustic treatment devices .

Fundamental limitations on Earth-like planet detection with extremely large telescopes

Abstract: We analyse the fundamental limitations for the detection of extraterrestrial planets with Extremely Large Telescopes. For this task, a coronagraphic device combined with a very high order wavefront correction system is required but is not sufficient to achieve the 10 -10 contrast level needed to detect an Earth-like planet. The stellar residuals left uncorrected by the wavefront correction system need to be calibrated and subtracted. We consider a general model including the dynamic phase aberrations downstream of the wavefront correction system, the static phase aberrations of the instrument and some differential aberrations provided by the calibration unit. A rather optimistic case of a filled circular pupil and of a perfect coronagraph is assumed. As a result of the analytical study, the limitation is found to mostly come from the static aberrations. We confirm this result using numerical simulations and evaluate the requirements in terms of phase aberrations to detect Earth-like planets with Extremely Large Telescopes.

THz-wave parametric oscillator with a surface-emitted configuration.

Abstract: We propose a surface-emitted cavity configuration for a terahertz-wave parametric oscillator that allows THz wave emission perpendicular to the crystal surface without any output coupler. The oscillating idler and pump waves are reflected at the surface of a nonlinear crystal in a single resonance cavity, satisfying the noncollinear phasematching condition. The radiated THz wave has a Gaussian profile. The measured beam quality factors (M(2)) were 1.15 and 1.25 in the horizontal and vertical directions, respectively. The measured tunable range was 0.8-2.74 THz. A test of transmission imaging using a test pattern was demonstrated.

Optical Scanning Device

Abstract: An optical scanning device for scanning an optical record carrier. The optical scanning device includes: a radiation source system (661; 761); an optical element (1; 101; 201; 301) comprising a first fluid (A) and a second fluid (B; C) separated from each other by a fluid meniscus (16; 116, 138; 216; 316) having an adjustable configuration; and a control system (20; 120; 220; 320) arranged to adjust the fluid meniscus configuration to introduce a first type of wavefront modification. The first type of wavefront modification causes the radiation beam to be redirected from an input radiation beam path (2; 102; 244; 348) onto one of a plurality of output radiation beam paths (24, 26; 140; 246; 350) which each have a different angular displacement (α, β, Ϝ, δ, e) from the input radiation beam path. The control system is further arranged to adjust the fluid meniscus configuration to introduce a second type of wavefront modification. The second type of wavefront modification is arranged to compensate a wavefront aberration of the radiation beam, the compensated wavefront aberration being adjusted in accordance with the angular displacement.

Interpreting interferometric height measurements using the instrument transfer function

Abstract: Much of this paper has emphasized the precariousness of using a linear ITF for what is fundamentally a nonlinear process of encoding height into the phase of a complex wave amplitude. A more accurate model begins with an explicit calculation of this amplitude, then propagates the wavefront through the system to determine what the instrument will do.

Three-flat test solutions based on simple mirror symmetry

Abstract: In interferometric surface and wavefront metrology, three-flat tests are the archetypes of measurement procedures to separate errors in the interferometer reference wavefront from errors due to the test part surface, so-called absolute tests. What is believed to be a new class of solutions of the three-flat problem for circular flats is described in terms of functions that are symmetric or antisymmetric with respect to reflections at a single line passing through the center of the flat surfaces. The new solutions are simpler and easier to calculate than the known solutions based on twofold mirror symmetry or rotation symmetry. Strategies for effective azimuthal averaging and a method for determining the averaging error are also discussed.