Wavefront sensorless adaptive optics ophthalmoscopy in the human eye

PubMed Central

Hofer, Heidi; Sredar, Nripun; Queener, Hope; Li, Chaohong; Porter, Jason

2011-01-01

Wavefront sensor noise and fidelity place a fundamental limit on achievable image quality in current adaptive optics ophthalmoscopes. Additionally, the wavefront sensor ‘beacon’ can interfere with visual experiments. We demonstrate real-time (25 Hz), wavefront sensorless adaptive optics imaging in the living human eye with image quality rivaling that of wavefront sensor based control in the same system. A stochastic parallel gradient descent algorithm directly optimized the mean intensity in retinal image frames acquired with a confocal adaptive optics scanning laser ophthalmoscope (AOSLO). When imaging through natural, undilated pupils, both control methods resulted in comparable mean image intensities. However, when imaging through dilated pupils, image intensity was generally higher following wavefront sensor-based control. Despite the typically reduced intensity, image contrast was higher, on average, with sensorless control. Wavefront sensorless control is a viable option for imaging the living human eye and future refinements of this technique may result in even greater optical gains. PMID:21934779

Wavefront control of large optical systems

NASA Technical Reports Server (NTRS)

Meinel, Aden B.; Meinel, Marjorie P.; Breckinridge, J. B.

1990-01-01

Several levels of wavefront control are necessary for the optimum performance of very large telescopes, especially segmented ones like the Large Deployable Reflector. In general, the major contributors to wavefront error are the segments of the large primary mirror. Wavefront control at the largest optical surface may not be the optimum choice because of the mass and inaccessibility of the elements of this surface that require upgrading. The concept of two-stage optics was developed to permit a poor wavefront from the large optics to be upgraded by means of a wavefront corrector at a small exit pupil of the system.

Investigation of Primary Mirror Segment's Residual Errors for the Thirty Meter Telescope

NASA Technical Reports Server (NTRS)

Seo, Byoung-Joon; Nissly, Carl; Angeli, George; MacMynowski, Doug; Sigrist, Norbert; Troy, Mitchell; Williams, Eric

2009-01-01

The primary mirror segment aberrations after shape corrections with warping harness have been identified as the single largest error term in the Thirty Meter Telescope (TMT) image quality error budget. In order to better understand the likely errors and how they will impact the telescope performance we have performed detailed simulations. We first generated unwarped primary mirror segment surface shapes that met TMT specifications. Then we used the predicted warping harness influence functions and a Shack-Hartmann wavefront sensor model to determine estimates for the 492 corrected segment surfaces that make up the TMT primary mirror. Surface and control parameters, as well as the number of subapertures were varied to explore the parameter space. The corrected segment shapes were then passed to an optical TMT model built using the Jet Propulsion Laboratory (JPL) developed Modeling and Analysis for Controlled Optical Systems (MACOS) ray-trace simulator. The generated exit pupil wavefront error maps provided RMS wavefront error and image-plane characteristics like the Normalized Point Source Sensitivity (PSSN). The results have been used to optimize the segment shape correction and wavefront sensor designs as well as provide input to the TMT systems engineering error budgets.

Waffle mode error in the AEOS adaptive optics point-spread function

NASA Astrophysics Data System (ADS)

Makidon, Russell B.; Sivaramakrishnan, Anand; Roberts, Lewis C., Jr.; Oppenheimer, Ben R.; Graham, James R.

2003-02-01

Adaptive optics (AO) systems have improved astronomical imaging capabilities significantly over the last decade, and have the potential to revolutionize the kinds of science done with 4-5m class ground-based telescopes. However, provided sufficient detailed study and analysis, existing AO systems can be improved beyond their original specified error budgets. Indeed, modeling AO systems has been a major activity in the past decade: sources of noise in the atmosphere and the wavefront sensing WFS) control loop have received a great deal of attention, and many detailed and sophisticated control-theoretic and numerical models predicting AO performance are already in existence. However, in terms of AO system performance improvements, wavefront reconstruction (WFR) and wavefront calibration techniques have commanded relatively little attention. We elucidate the nature of some of these reconstruction problems, and demonstrate their existence in data from the AEOS AO system. We simulate the AO correction of AEOS in the I-band, and show that the magnitude of the `waffle mode' error in the AEOS reconstructor is considerably larger than expected. We suggest ways of reducing the magnitude of this error, and, in doing so, open up ways of understanding how wavefront reconstruction might handle bad actuators and partially-illuminated WFS subapertures.

Fundamental performance of transverse wind estimator from Shack-Hartmann wave-front sensor measurements.

PubMed

Li, Zhenghan; Li, Xinyang

2018-04-30

Real time transverse wind estimation contributes to predictive correction which is used to compensate for the time delay error in the control systems of adaptive optics (AO) system. Many methods that apply Shack-Hartmann wave-front sensor to wind profile measurement have been proposed. One of the obvious problems is the lack of a fundamental benchmark to compare the various methods. In this work, we present the fundamental performance limits for transverse wind estimator from Shack-Hartmann wave-front sensor measurements using Cramér-Rao lower bound (CRLB). The bound provides insight into the nature of the transverse wind estimation, thereby suggesting how to design and improve the estimator in the different application scenario. We analyze the theoretical bound and find that factors such as slope measurement noise, wind velocity and atmospheric coherence length r 0 have important influence on the performance. Then, we introduced the non-iterative gradient-based transverse wind estimator. The source of the deterministic bias of the gradient-based transverse wind estimators is analyzed for the first time. Finally, we derived biased CRLB for the gradient-based transverse wind estimators from Shack-Hartmann wave-front sensor measurements and the bound can predict the performance of estimator more accurately.

Active Mirror Predictive and Requirements Verification Software (AMP-ReVS)

NASA Technical Reports Server (NTRS)

Basinger, Scott A.

2012-01-01

This software is designed to predict large active mirror performance at various stages in the fabrication lifecycle of the mirror. It was developed for 1-meter class powered mirrors for astronomical purposes, but is extensible to other geometries. The package accepts finite element model (FEM) inputs and laboratory measured data for large optical-quality mirrors with active figure control. It computes phenomenological contributions to the surface figure error using several built-in optimization techniques. These phenomena include stresses induced in the mirror by the manufacturing process and the support structure, the test procedure, high spatial frequency errors introduced by the polishing process, and other process-dependent deleterious effects due to light-weighting of the mirror. Then, depending on the maturity of the mirror, it either predicts the best surface figure error that the mirror will attain, or it verifies that the requirements for the error sources have been met once the best surface figure error has been measured. The unique feature of this software is that it ties together physical phenomenology with wavefront sensing and control techniques and various optimization methods including convex optimization, Kalman filtering, and quadratic programming to both generate predictive models and to do requirements verification. This software combines three distinct disciplines: wavefront control, predictive models based on FEM, and requirements verification using measured data in a robust, reusable code that is applicable to any large optics for ground and space telescopes. The software also includes state-of-the-art wavefront control algorithms that allow closed-loop performance to be computed. It allows for quantitative trade studies to be performed for optical systems engineering, including computing the best surface figure error under various testing and operating conditions. After the mirror manufacturing process and testing have been completed, the software package can be used to verify that the underlying requirements have been met.

Zernike Wavefront Sensor Modeling Development for LOWFS on WFIRST-AFTA

NASA Technical Reports Server (NTRS)

Wang, Xu; Wallace, J. Kent; Shi, Fang

2015-01-01

WFIRST-AFTA design makes use of an existing 2.4m telescope for direct imaging of exoplanets. To maintain the high contrast needed for the coronagraph, wavefront error (WFE) of the optical system needs to be continuously sensed and controlled. Low Order Wavefront Sensing (LOWFS) uses the rejected starlight from an immediate focal plane to sense wavefront changes (mostly thermally induced low order WFE) by combining the LOWFS mask (a phase plate located at the small center region with reflective layer) with the starlight rejection masks, i.e. Hybrid Lyot Coronagraph (HLC)'s occulter or Shaped Pupil Coronagraph (SPC)'s field stop. Zernike wavefront sensor (ZWFS) measures phase via the phase-contrast method and is known to be photon noise optimal for measuring low order aberrations. Recently, ZWFS was selected as the baseline LOWFS technology on WFIST/AFTA for its good sensitivity, accuracy, and its easy integration with the starlight rejection mask. In this paper, we review the theory of ZWFS operation, describe the ZWFS algorithm development, and summarize various numerical sensitivity studies on the sensor performance. In the end, the predicted sensor performance on SPC and HLC configurations are presented.

Dynamic wavefront creation for processing units using a hybrid compactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puthoor, Sooraj; Beckmann, Bradford M.; Yudanov, Dmitri

A method, a non-transitory computer readable medium, and a processor for repacking dynamic wavefronts during program code execution on a processing unit, each dynamic wavefront including multiple threads are presented. If a branch instruction is detected, a determination is made whether all wavefronts following a same control path in the program code have reached a compaction point, which is the branch instruction. If no branch instruction is detected in executing the program code, a determination is made whether all wavefronts following the same control path have reached a reconvergence point, which is a beginning of a program code segment tomore » be executed by both a taken branch and a not taken branch from a previous branch instruction. The dynamic wavefronts are repacked with all threads that follow the same control path, if all wavefronts following the same control path have reached the branch instruction or the reconvergence point.« less

An Improved Wavefront Control Algorithm for Large Space Telescopes

NASA Technical Reports Server (NTRS)

Sidick, Erkin; Basinger, Scott A.; Redding, David C.

2008-01-01

Wavefront sensing and control is required throughout the mission lifecycle of large space telescopes such as James Webb Space Telescope (JWST). When an optic of such a telescope is controlled with both surface-deforming and rigid-body actuators, the sensitivity-matrix obtained from the exit pupil wavefront vector divided by the corresponding actuator command value can sometimes become singular due to difference in actuator types and in actuator command values. In this paper, we propose a simple approach for preventing a sensitivity-matrix from singularity. We also introduce a new "minimum-wavefront and optimal control compensator". It uses an optimal control gain matrix obtained by feeding back the actuator commands along with the measured or estimated wavefront phase information to the estimator, thus eliminating the actuator modes that are not observable in the wavefront sensing process.

Filter Function for Wavefront Sensing Over a Field of View

NASA Technical Reports Server (NTRS)

Dean, Bruce H.

2007-01-01

A filter function has been derived as a means of optimally weighting the wavefront estimates obtained in image-based phase retrieval performed at multiple points distributed over the field of view of a telescope or other optical system. When the data obtained in wavefront sensing and, more specifically, image-based phase retrieval, are used for controlling the shape of a deformable mirror or other optic used to correct the wavefront, the control law obtained by use of the filter function gives a more balanced optical performance over the field of view than does a wavefront-control law obtained by use of a wavefront estimate obtained from a single point in the field of view.

Low Order Wavefront Sensing and Control for WFIRST-AFTA Coronagraph

NASA Technical Reports Server (NTRS)

Shi, Fang; Balasubramanian, Kunjithapatha; Bartos, Randall; Hien, Randall; Kern, Brian; Krist, John; Lam, Raymond; Moore, Douglas; Moore, James; Patterson, Keith;

Wavefront control in adaptive microscopy using Shack-Hartmann sensors with arbitrarily shaped pupils.

PubMed

Dong, Bing; Booth, Martin J

2018-01-22

In adaptive optical microscopy of thick biological tissue, strong scattering and aberrations can change the effective pupil shape by rendering some Shack-Hartmann spots unusable. The change of pupil shape leads to a change of wavefront reconstruction or control matrix that should be updated accordingly. Modified slope and modal wavefront control methods based on measurements of a Shack-Hartmann wavefront sensor are proposed to accommodate an arbitrarily shaped pupil. Furthermore, we present partial wavefront control methods that remove specific aberration modes like tip, tilt and defocus from the control loop. The proposed control methods were investigated and compared by simulation using experimentally obtained aberration data. The performance was then tested experimentally through closed-loop aberration corrections using an obscured pupil.

Beam wavefront and farfield control for ICF laser driver

NASA Astrophysics Data System (ADS)

Dai, Wanjun; Deng, Wu; Zhang, Xin; Jiang, Xuejun; Zhang, Kun; Zhou, Wei; Zhao, Junpu; Hu, Dongxia

2010-10-01

Five main problems of beam wavefront and farfield control in ICF laser driver are synthetically discussed, including control requirements, beam propagation principle, distortions source control, system design and adjustment optimization, active wavefront correction technology. We demonstrate that beam can be propagated well and the divergence angle of the TIL pulses can be improved to less than 60μrad with solving these problems, which meets the requirements of TIL. The results can provide theoretical and experimental support for wavefront and farfield control designing requirements of the next large scale ICF driver.

A wavefront compensation approach to segmented mirror figure control

NASA Technical Reports Server (NTRS)

Redding, David; Breckenridge, Bill; Sevaston, George; Lau, Ken

1991-01-01

We consider the 'figure-control' problem for a spaceborn sub-millimeter wave telescope, the Precision Segmented Reflector Project Focus Mission Telescope. We show that performance of any figure control system is subject to limits on the controllability and observability of the quality of the wavefront. We present a wavefront-compensation method for the Focus Mission Telescope which uses mirror-figure sensors and three-axis segment actuator to directly minimize wavefront errors due to segment position errors. This approach shows significantly better performance when compared with a panel-state-compensation approach.

Initial Performance of the Keck AO Wavefront Controller System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johansson, E M; Acton, D S; An, J R

2001-03-01

The wavefront controller for the Keck Observatory AO system consists of two separate real-time control loops: a tip-tilt control loop to remove tilt from the incoming wavefront, and a deformable mirror control loop to remove higher-order aberrations. In this paper, we describe these control loops and analyze their performance using diagnostic data acquired during the integration and testing of the AO system on the telescope. Disturbance rejection curves for the controllers are calculated from the experimental data and compared to theory. The residual wavefront errors due to control loop bandwidth are also calculated from the data, and possible improvements tomore » the controller performance are discussed.« less

Wavefront Engineering with Phase Discontinuities: Designer Interfaces for High Performance Planar Optical Components

DTIC Science & Technology

2015-08-27

ABSTRACT The PI and his group opened up new directions of research: the generation of vector beams with metasurfaces that control amplitude, phase...and polarization of wavefronts, the detection of wavefronts using metasurfaces , new metasurfaces for controlling surface plasmon wavefronts and high...performance device applications of metasurfaces on graphene. In the vector beam area they generated radially polarized light with a single

Iris registration in wavefront-guided LASIK to correct mixed astigmatism.

PubMed

Khalifa, Mounir; El-Kateb, Mohamed; Shaheen, Mohamed Shafik

2009-03-01

To investigate the predictability, safety, and efficiency of wavefront-guided laser in situ keratomileusis (LASIK) with iris-registration technology to correct mixed astigmatism. Vision correction center, Alexandria, Egypt. This retrospective double-blind study included randomly selected patients with mixed astigmatism who sought laser refractive surgery. Patients were divided equally into 3 groups and treated with conventional LASIK and manual marking, wavefront-guided LASIK and manual marking, or wavefront-guided LASIK with iris registration (LASIK+IR group). Eyes were analyzed preoperatively and up to 3 months postoperatively. The LASIK+IR group had better postoperative uncorrected visual acuity (100% 20/30 or better; 90% 20/20 or better; 20% 20/16 or better) than the other groups and did not lose preoperative best spectacle-corrected visual acuity, unlike the other groups. This group also had the highest percentage of eyes that gained lines of acuity (20% 1 line; 10% 2 lines). The LASIK+IR group had the highest predictability of spherical refraction (80% within +/-0.50 diopter [D]; 100% within +/-1.00 D [P<.05] and the highest predictability of cylinder refraction. The LASIK+IR eyes had a significantly smaller increase postoperatively in coma, trefoil, and secondary astigmatism. There was no significant difference between groups in spherical aberration or quadrafoil. The LASIK-IR group had the most improvement in scotopic contrast sensitivity (P<.05). Wavefront-guided LASIK with iris registration was more predictable, safe, and efficient than conventional or wavefront-guided LASIK with manual marking in correcting mixed astigmatism. Further studies are needed to confirm these results.

Design and tolerance analysis of a transmission sphere by interferometer model

NASA Astrophysics Data System (ADS)

Peng, Wei-Jei; Ho, Cheng-Fong; Lin, Wen-Lung; Yu, Zong-Ru; Huang, Chien-Yao; Hsu, Wei-Yao

2015-09-01

The design of a 6-in, f/2.2 transmission sphere for Fizeau interferometry is presented in this paper. To predict the actual performance during design phase, we build an interferometer model combined with tolerance analysis in Zemax. Evaluating focus imaging is not enough for a double pass optical system. Thus, we study the interferometer model that includes system error, wavefronts reflected from reference surface and tested surface. Firstly, we generate a deformation map of the tested surface. Because of multiple configurations in Zemax, we can get the test wavefront and the reference wavefront reflected from the tested surface and the reference surface of transmission sphere respectively. According to the theory of interferometry, we subtract both wavefronts to acquire the phase of tested surface. Zernike polynomial is applied to transfer the map from phase to sag and to remove piston, tilt and power. The restored map is the same as original map; because of no system error exists. Secondly, perturbed tolerances including fabrication of lenses and assembly are considered. The system error occurs because the test and reference beam are no longer common path perfectly. The restored map is inaccurate while the system error is added. Although the system error can be subtracted by calibration, it should be still controlled within a small range to avoid calibration error. Generally the reference wavefront error including the system error and the irregularity of the reference surface of 6-in transmission sphere is measured within peak-to-valley (PV) 0.1 λ (λ=0.6328 um), which is not easy to approach. Consequently, it is necessary to predict the value of system error before manufacture. Finally, a prototype is developed and tested by a reference surface with PV 0.1 λ irregularity.

Optical Modeling Activities for NASA's James Webb Space Telescope (JWST): V. Operational Alignment Updates

NASA Technical Reports Server (NTRS)

Howard, Joseph M.; Ha, Kong Q.; Shiri, Ron; Smith, J. Scott; Mosier, Gary; Muheim, Danniella

2008-01-01

This paper is part five of a series on the ongoing optical modeling activities for the James Webb Space Telescope (JWST). The first two papers discussed modeling JWST on-orbit performance using wavefront sensitivities to predict line of sight motion induced blur, and stability during thermal transients. The third paper investigates the aberrations resulting from alignment and figure compensation of the controllable degrees of freedom (primary and secondary mirrors), which may be encountered during ground alignment and on-orbit commissioning of the observatory, and the fourth introduced the software toolkits used to perform much of the optical analysis for JWST. The work here models observatory operations by simulating line-of-sight image motion and alignment drifts over a two-week period. Alignment updates are then simulated using wavefront sensing and control processes to calculate and perform the corrections. A single model environment in Matlab is used for evaluating the predicted performance of the observatory during these operations.

Wavefront control system for the Keck telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brase, J. M., LLNL

1998-03-01

The laser guide star adaptive optics system currently being developed for the Keck 2 telescope consists of several major subsystems: the optical bench, wavefront control, user interface and supervisory control, and the laser system. The paper describes the design and implementation of the wavefront control subsystem that controls a 349 actuator deformable mirror for high order correction and tip-tilt mirrors for stabilizing the image and laser positions.

Developmental Cryogenic Active Telescope Testbed, a Wavefront Sensing and Control Testbed for the Next Generation Space Telescope

NASA Technical Reports Server (NTRS)

Leboeuf, Claudia M.; Davila, Pamela S.; Redding, David C.; Morell, Armando; Lowman, Andrew E.; Wilson, Mark E.; Young, Eric W.; Pacini, Linda K.; Coulter, Dan R.

1998-01-01

As part of the technology validation strategy of the next generation space telescope (NGST), a system testbed is being developed at GSFC, in partnership with JPL and Marshall Space Flight Center (MSFC), which will include all of the component functions envisioned in an NGST active optical system. The system will include an actively controlled, segmented primary mirror, actively controlled secondary, deformable, and fast steering mirrors, wavefront sensing optics, wavefront control algorithms, a telescope simulator module, and an interferometric wavefront sensor for use in comparing final obtained wavefronts from different tests. The developmental. cryogenic active telescope testbed (DCATT) will be implemented in three phases. Phase 1 will focus on operating the testbed at ambient temperature. During Phase 2, a cryocapable segmented telescope will be developed and cooled to cryogenic temperature to investigate the impact on the ability to correct the wavefront and stabilize the image. In Phase 3, it is planned to incorporate industry developed flight-like components, such as figure controlled mirror segments, cryogenic, low hold power actuators, or different wavefront sensing and control hardware or software. A very important element of the program is the development and subsequent validation of the integrated multidisciplinary models. The Phase 1 testbed objectives, plans, configuration, and design will be discussed.

MEMS deformable mirror embedded wavefront sensing and control system

NASA Astrophysics Data System (ADS)

Owens, Donald; Schoen, Michael; Bush, Keith

2006-01-01

Electrostatic Membrane Deformable Mirror (MDM) technology developed using silicon bulk micro-machining techniques offers the potential of providing low-cost, compact wavefront control systems for diverse optical system applications. Electrostatic mirror construction using bulk micro-machining allows for custom designs to satisfy wavefront control requirements for most optical systems. An electrostatic MDM consists of a thin membrane, generally with a thin metal or multi-layer high-reflectivity coating, suspended over an actuator pad array that is connected to a high-voltage driver. Voltages applied to the array elements deflect the membrane to provide an optical surface capable of correcting for measured optical aberrations in a given system. Electrostatic membrane DM designs are derived from well-known principles of membrane mechanics and electrostatics, the desired optical wavefront control requirements, and the current limitations of mirror fabrication and actuator drive electronics. MDM performance is strongly dependent on mirror diameter and air damping in meeting desired spatial and temporal frequency requirements. In this paper, we present wavefront control results from an embedded wavefront control system developed around a commercially available high-speed camera and an AgilOptics Unifi MDM driver using USB 2.0 communications and the Linux development environment. This new product, ClariFast TM, combines our previous Clarifi TM product offering into a faster more streamlined version dedicated strictly to Hartmann Wavefront sensing.

Keck adaptive optics: control subsystem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brase, J.M.; An, J.; Avicola, K.

1996-03-08

Adaptive optics on the Keck 10 meter telescope will provide an unprecedented level of capability in high resolution ground based astronomical imaging. The system is designed to provide near diffraction limited imaging performance with Strehl {gt} 0.3 n median Keck seeing of r0 = 25 cm, T =10 msec at 500 nm wavelength. The system will be equipped with a 20 watt sodium laser guide star to provide nearly full sky coverage. The wavefront control subsystem is responsible for wavefront sensing and the control of the tip-tilt and deformable mirrors which actively correct atmospheric turbulence. The spatial sampling interval formore » the wavefront sensor and deformable mirror is de=0.56 m which gives us 349 actuators and 244 subapertures. This paper summarizes the wavefront control system and discusses particular issues in designing a wavefront controller for the Keck telescope.« less

Wavefront control with a spatial light modulator containing dual-frequency liquid crystal

NASA Astrophysics Data System (ADS)

Gu, Dong-Feng; Winker, Bruce; Wen, Bing; Taber, Don; Brackley, Andrew; Wirth, Allan; Albanese, Marc; Landers, Frank

2004-10-01

A versatile, scalable wavefront control approach based upon proven liquid crystal (LC) spatial light modulator (SLM) technology was extended for potential use in high-energy near-infrared laser applications. The reflective LC SLM module demonstrated has a two-inch diameter active aperture with 812 pixels. Using an ultra-low absorption transparent conductor in the LC SLM, a high laser damage threshold was demonstrated. Novel dual frequency liquid crystal materials and addressing schemes were implemented to achieve fast switching speed (<1ms at 1.31 microns). Combining this LCSLM with a novel wavefront sensing method, a closed loop wavefront controller is being demonstrated. Compared to conventional deformable mirrors, this non-mechanical wavefront control approach offers substantial improvements in speed (bandwidth), resolution, power consumption and system weight/volume.

Advanced Wavefront Control Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olivier, S S; Brase, J M; Avicola, K

2001-02-21

Programs at LLNL that involve large laser systems--ranging from the National Ignition Facility to new tactical laser weapons--depend on the maintenance of laser beam quality through precise control of the optical wavefront. This can be accomplished using adaptive optics, which compensate for time-varying aberrations that are often caused by heating in a high-power laser system. Over the past two decades, LLNL has developed a broad capability in adaptive optics technology for both laser beam control and high-resolution imaging. This adaptive optics capability has been based on thin deformable glass mirrors with individual ceramic actuators bonded to the back. In themore » case of high-power lasers, these adaptive optics systems have successfully improved beam quality. However, as we continue to extend our applications requirements, the existing technology base for wavefront control cannot satisfy them. To address this issue, this project studied improved modeling tools to increase our detailed understanding of the performance of these systems, and evaluated novel approaches to low-order wavefront control that offer the possibility of reduced cost and complexity. We also investigated improved beam control technology for high-resolution wavefront control. Many high-power laser systems suffer from high-spatial-frequency aberrations that require control of hundreds or thousands of phase points to provide adequate correction. However, the cost and size of current deformable mirrors can become prohibitive for applications requiring more than a few tens of phase control points. New phase control technologies are becoming available which offer control of many phase points with small low-cost devices. The goal of this project was to expand our wavefront control capabilities with improved modeling tools, new devices that reduce system cost and complexity, and extensions to high spatial and temporal frequencies using new adaptive optics technologies. In FY 99, the second year of this project, work was performed in four areas (1) advanced modeling tools for deformable mirrors (2) low-order wavefront correctors with Alvarez lenses, (3) a direct phase measuring heterdyne wavefront sensor, and (4) high-spatial-frequency wavefront control using spatial light modulators.« less

Systems and Methods for Automated Vessel Navigation Using Sea State Prediction

NASA Technical Reports Server (NTRS)

Huntsberger, Terrance L. (Inventor); Howard, Andrew B. (Inventor); Reinhart, Rene Felix (Inventor); Aghazarian, Hrand (Inventor); Rankin, Arturo (Inventor)

2017-01-01

Systems and methods for sea state prediction and autonomous navigation in accordance with embodiments of the invention are disclosed. One embodiment of the invention includes a method of predicting a future sea state including generating a sequence of at least two 3D images of a sea surface using at least two image sensors, detecting peaks and troughs in the 3D images using a processor, identifying at least one wavefront in each 3D image based upon the detected peaks and troughs using the processor, characterizing at least one propagating wave based upon the propagation of wavefronts detected in the sequence of 3D images using the processor, and predicting a future sea state using at least one propagating wave characterizing the propagation of wavefronts in the sequence of 3D images using the processor. Another embodiment includes a method of autonomous vessel navigation based upon a predicted sea state and target location.

Systems and Methods for Automated Vessel Navigation Using Sea State Prediction

NASA Technical Reports Server (NTRS)

Aghazarian, Hrand (Inventor); Reinhart, Rene Felix (Inventor); Huntsberger, Terrance L. (Inventor); Rankin, Arturo (Inventor); Howard, Andrew B. (Inventor)

2015-01-01

Systems and methods for sea state prediction and autonomous navigation in accordance with embodiments of the invention are disclosed. One embodiment of the invention includes a method of predicting a future sea state including generating a sequence of at least two 3D images of a sea surface using at least two image sensors, detecting peaks and troughs in the 3D images using a processor, identifying at least one wavefront in each 3D image based upon the detected peaks and troughs using the processor, characterizing at least one propagating wave based upon the propagation of wavefronts detected in the sequence of 3D images using the processor, and predicting a future sea state using at least one propagating wave characterizing the propagation of wavefronts in the sequence of 3D images using the processor. Another embodiment includes a method of autonomous vessel navigation based upon a predicted sea state and target location.

Dichroic beamsplitter for high energy laser diagnostics

DOEpatents

LaFortune, Kai N [Livermore, CA; Hurd, Randall [Tracy, CA; Fochs, Scott N [Livermore, CA; Rotter, Mark D [San Ramon, CA; Hackel, Lloyd [Livermore, CA

2011-08-30

Wavefront control techniques are provided for the alignment and performance optimization of optical devices. A Shack-Hartmann wavefront sensor can be used to measure the wavefront distortion and a control system generates feedback error signal to optics inside the device to correct the wavefront. The system can be calibrated with a low-average-power probe laser. An optical element is provided to couple the optical device to a diagnostic/control package in a way that optimizes both the output power of the optical device and the coupling of the probe light into the diagnostics.

Dual-thread parallel control strategy for ophthalmic adaptive optics.

PubMed

Yu, Yongxin; Zhang, Yuhua

To improve ophthalmic adaptive optics speed and compensate for ocular wavefront aberration of high temporal frequency, the adaptive optics wavefront correction has been implemented with a control scheme including 2 parallel threads; one is dedicated to wavefront detection and the other conducts wavefront reconstruction and compensation. With a custom Shack-Hartmann wavefront sensor that measures the ocular wave aberration with 193 subapertures across the pupil, adaptive optics has achieved a closed loop updating frequency up to 110 Hz, and demonstrated robust compensation for ocular wave aberration up to 50 Hz in an adaptive optics scanning laser ophthalmoscope.

Dual-thread parallel control strategy for ophthalmic adaptive optics

PubMed Central

Yu, Yongxin; Zhang, Yuhua

2015-01-01

To improve ophthalmic adaptive optics speed and compensate for ocular wavefront aberration of high temporal frequency, the adaptive optics wavefront correction has been implemented with a control scheme including 2 parallel threads; one is dedicated to wavefront detection and the other conducts wavefront reconstruction and compensation. With a custom Shack-Hartmann wavefront sensor that measures the ocular wave aberration with 193 subapertures across the pupil, adaptive optics has achieved a closed loop updating frequency up to 110 Hz, and demonstrated robust compensation for ocular wave aberration up to 50 Hz in an adaptive optics scanning laser ophthalmoscope. PMID:25866498

Study of a MEMS-based Shack-Hartmann wavefront sensor with adjustable pupil sampling for astronomical adaptive optics.

PubMed

Baranec, Christoph; Dekany, Richard

2008-10-01

We introduce a Shack-Hartmann wavefront sensor for adaptive optics that enables dynamic control of the spatial sampling of an incoming wavefront using a segmented mirror microelectrical mechanical systems (MEMS) device. Unlike a conventional lenslet array, subapertures are defined by either segments or groups of segments of a mirror array, with the ability to change spatial pupil sampling arbitrarily by redefining the segment grouping. Control over the spatial sampling of the wavefront allows for the minimization of wavefront reconstruction error for different intensities of guide source and different atmospheric conditions, which in turn maximizes an adaptive optics system's delivered Strehl ratio. Requirements for the MEMS devices needed in this Shack-Hartmann wavefront sensor are also presented.

Feedback controlled optics with wavefront compensation

NASA Technical Reports Server (NTRS)

Breckenridge, William G. (Inventor); Redding, David C. (Inventor)

1993-01-01

The sensitivity model of a complex optical system obtained by linear ray tracing is used to compute a control gain matrix by imposing the mathematical condition for minimizing the total wavefront error at the optical system's exit pupil. The most recent deformations or error states of the controlled segments or optical surfaces of the system are then assembled as an error vector, and the error vector is transformed by the control gain matrix to produce the exact control variables which will minimize the total wavefront error at the exit pupil of the optical system. These exact control variables are then applied to the actuators controlling the various optical surfaces in the system causing the immediate reduction in total wavefront error observed at the exit pupil of the optical system.

WFIRST: Managing Telescope Wavefront Stability to Meet Coronagraph Performance

NASA Astrophysics Data System (ADS)

Noecker, Martin; Poberezhskiy, Ilya; Kern, Brian; Krist, John; WFIRST System Engineering Team

2018-01-01

The WFIRST coronagraph instrument (CGI) needs a stable telescope and active wavefront control to perform coronagraph science with an expected sensitivity of 8x10-9 in the exoplanet-star flux ratio (SNR=10) at 200 milliarcseconds angular separation. With its subnanometer requirements on the stability of its input wavefront error (WFE), the CGI employs a combination of pointing and wavefront control loops and thermo-mechanical stability to meet budget allocations for beam-walk and low-order WFE, which enable stable starlight speckles on the science detector that can be removed by image subtraction. We describe the control strategy and the budget framework for estimating and budgeting the elements of wavefront stability, and the modeling strategy to evaluate it.

Fourier transform wavefront control with adaptive prediction of the atmosphere.

PubMed

Poyneer, Lisa A; Macintosh, Bruce A; Véran, Jean-Pierre

2007-09-01

Predictive Fourier control is a temporal power spectral density-based adaptive method for adaptive optics that predicts the atmosphere under the assumption of frozen flow. The predictive controller is based on Kalman filtering and a Fourier decomposition of atmospheric turbulence using the Fourier transform reconstructor. It provides a stable way to compensate for arbitrary numbers of atmospheric layers. For each Fourier mode, efficient and accurate algorithms estimate the necessary atmospheric parameters from closed-loop telemetry and determine the predictive filter, adjusting as conditions change. This prediction improves atmospheric rejection, leading to significant improvements in system performance. For a 48x48 actuator system operating at 2 kHz, five-layer prediction for all modes is achievable in under 2x10(9) floating-point operations/s.

Phase-Controlled Magnetic Mirror for Wavefront Correction

NASA Technical Reports Server (NTRS)

Hagopian, John; Wollack, Edward

2011-01-01

Typically, light interacts with matter via the electric field and interaction with weakly bound electrons. In a magnetic mirror, a patterned nanowire is fabricated over a metallic layer with a dielectric layer in between. Oscillation of the electrons in the nanowires in response to the magnetic field of incident photons causes a re-emission of photons and operation as a "magnetic mirror." By controlling the index of refraction in the dielectric layer using a local applied voltage, the phase of the emitted radiation can be controlled. This allows electrical modification of the reflected wavefront, resulting in a deformable mirror that can be used for wavefront control. Certain applications require wavefront quality in the few-nanometer regime, which is a major challenge for optical fabrication and alignment of mirrors or lenses. The use of a deformable magnetic mirror allows for a device with no moving parts that can modify the phase of incident light over many spatial scales, potentially with higher resolution than current approaches. Current deformable mirrors modify the incident wavefront by using nano-actuation of a substrate to physically bend the mirror to a desired shape. The purpose of the innovation is to modify the incident wavefront for the purpose of correction of fabrication and alignment-induced wavefront errors at the system level. The advanced degree of precision required for some applications such as gravity wave detection (LISA - Laser Interferometer Space Antenna) or planet finding (FKSI - Fourier-Kelvin Stellar Interferometer) requires wavefront control at the limits of the current state of the art. All the steps required to fabricate a magnetic mirror have been demonstrated. The modification is to apply a bias voltage to the dielectric layer so as to change the index of refraction and modify the phase of the reflected radiation. Light is reflected off the device and collected by a phase-sensing interferometer. The interferometer determines the initial wavefront of the device and fore optics. A wavefront correction is calculated, and voltage profile for each nanowire strip is determined. The voltage is applied, modifying the local index of refraction of the dielectric under the nanowire strip. This modifies the phase of the reflected light to allow wavefront correction.

Eye-pupil displacement and prediction: effects on residual wavefront in adaptive optics retinal imaging

PubMed Central

Kulcsár, Caroline; Raynaud, Henri-François; Garcia-Rissmann, Aurea

2016-01-01

This paper studies the effect of pupil displacements on the best achievable performance of retinal imaging adaptive optics (AO) systems, using 52 trajectories of horizontal and vertical displacements sampled at 80 Hz by a pupil tracker (PT) device on 13 different subjects. This effect is quantified in the form of minimal root mean square (rms) of the residual phase affecting image formation, as a function of the delay between PT measurement and wavefront correction. It is shown that simple dynamic models identified from data can be used to predict horizontal and vertical pupil displacements with greater accuracy (in terms of average rms) over short-term time horizons. The potential impact of these improvements on residual wavefront rms is investigated. These results allow to quantify the part of disturbances corrected by retinal imaging systems that are caused by relative displacements of an otherwise fixed or slowy-varying subject-dependent aberration. They also suggest that prediction has a limited impact on wavefront rms and that taking into account PT measurements in real time improves the performance of AO retinal imaging systems. PMID:27231607

Influence of wave-front sampling in adaptive optics retinal imaging

PubMed Central

Laslandes, Marie; Salas, Matthias; Hitzenberger, Christoph K.; Pircher, Michael

2017-01-01

A wide range of sampling densities of the wave-front has been used in retinal adaptive optics (AO) instruments, compared to the number of corrector elements. We developed a model in order to characterize the link between number of actuators, number of wave-front sampling points and AO correction performance. Based on available data from aberration measurements in the human eye, 1000 wave-fronts were generated for the simulations. The AO correction performance in the presence of these representative aberrations was simulated for different deformable mirror and Shack Hartmann wave-front sensor combinations. Predictions of the model were experimentally tested through in vivo measurements in 10 eyes including retinal imaging with an AO scanning laser ophthalmoscope. According to our study, a ratio between wavefront sampling points and actuator elements of 2 is sufficient to achieve high resolution in vivo images of photoreceptors. PMID:28271004

Spatial-temporal-covariance-based modeling, analysis, and simulation of aero-optics wavefront aberrations.

PubMed

Vogel, Curtis R; Tyler, Glenn A; Wittich, Donald J

2014-07-01

We introduce a framework for modeling, analysis, and simulation of aero-optics wavefront aberrations that is based on spatial-temporal covariance matrices extracted from wavefront sensor measurements. Within this framework, we present a quasi-homogeneous structure function to analyze nonhomogeneous, mildly anisotropic spatial random processes, and we use this structure function to show that phase aberrations arising in aero-optics are, for an important range of operating parameters, locally Kolmogorov. This strongly suggests that the d5/3 power law for adaptive optics (AO) deformable mirror fitting error, where d denotes actuator separation, holds for certain important aero-optics scenarios. This framework also allows us to compute bounds on AO servo lag error and predictive control error. In addition, it provides us with the means to accurately simulate AO systems for the mitigation of aero-effects, and it may provide insight into underlying physical processes associated with turbulent flow. The techniques introduced here are demonstrated using data obtained from the Airborne Aero-Optics Laboratory.

Optimal wavefront control for adaptive segmented mirrors

NASA Technical Reports Server (NTRS)

Downie, John D.; Goodman, Joseph W.

1989-01-01

A ground-based astronomical telescope with a segmented primary mirror will suffer image-degrading wavefront aberrations from at least two sources: (1) atmospheric turbulence and (2) segment misalignment or figure errors of the mirror itself. This paper describes the derivation of a mirror control feedback matrix that assumes the presence of both types of aberration and is optimum in the sense that it minimizes the mean-squared residual wavefront error. Assumptions of the statistical nature of the wavefront measurement errors, atmospheric phase aberrations, and segment misalignment errors are made in the process of derivation. Examples of the degree of correlation are presented for three different types of wavefront measurement data and compared to results of simple corrections.

Wavefront correction for static and dynamic aberrations to within 1 second of the system shot in the NIF Beamlet demonstration facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartley, R.; Kartz, M.; Behrendt, W.

1996-10-01

The laser wavefront of the NIF Beamlet demonstration system is corrected for static aberrations with a wavefront control system. The system operates closed loop with a probe beam prior to a shot and has a loop bandwidth of about 3 Hz. However, until recently the wavefront control system was disabled several minutes prior to the shot to allow time to manually reconfigure its attenuators and probe beam insertion mechanism to shot mode. Thermally-induced dynamic variations in gas density in the Beamlet main beam line produce significant wavefront error. After about 5-8 seconds, the wavefront error has increased to a new,more » higher level due to turbulence- induced aberrations no longer being corrected- This implies that there is a turbulence-induced aberration noise bandwidth of less than one Hertz, and that the wavefront controller could correct for the majority of turbulence-induced aberration (about one- third wave) by automating its reconfiguration to occur within one second of the shot, This modification was recently implemented on Beamlet; we call this modification the t{sub 0}-1 system.« less

Telescope Multi-Field Wavefront Control with a Kalman Filter

NASA Technical Reports Server (NTRS)

Lou, John Z.; Redding, David; Sigrist, Norbert; Basinger, Scott

2008-01-01

An effective multi-field wavefront control (WFC) approach is demonstrated for an actuated, segmented space telescope using wavefront measurements at the exit pupil, and the optical and computational implications of this approach are discussed. The integration of a Kalman Filter as an optical state estimator into the wavefront control process to further improve the robustness of the optical alignment of the telescope will also be discussed. Through a comparison of WFC performances between on-orbit and ground-test optical system configurations, the connection (and a possible disconnection) between WFC and optical system alignment under these circumstances are analyzed. Our MACOS-based computer simulation results will be presented and discussed.

The wavefront of the radio signal emitted by cosmic ray air showers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apel, W.D.; Bekk, K.; Blümer, J.

2014-09-01

Analyzing measurements of the LOPES antenna array together with corresponding CoREAS simulations for more than 300 measured events with energy above 10{sup 17} eV and zenith angles smaller than 45{sup o}, we find that the radio wavefront of cosmic-ray air showers is of approximately hyperbolic shape. The simulations predict a slightly steeper wavefront towards East than towards West, but this asymmetry is negligible against the measurement uncertainties of LOPES. At axis distances ∼> 50 m, the wavefront can be approximated by a simple cone. According to the simulations, the cone angle is clearly correlated with the shower maximum. Thus, we confirmmore » earlier predictions that arrival time measurements can be used to study the longitudinal shower development, but now using a realistic wavefront. Moreover, we show that the hyperbolic wavefront is compatible with our measurement, and we present several experimental indications that the cone angle is indeed sensitive to the shower development. Consequently, the wavefront can be used to statistically study the primary composition of ultra-high energy cosmic rays. At LOPES, the experimentally achieved precision for the shower maximum is limited by measurement uncertainties to approximately 140 g/c {sup 2}. But the simulations indicate that under better conditions this method might yield an accuracy for the atmospheric depth of the shower maximum, X{sub max}, better than 30 g/c {sup 2}. This would be competitive with the established air-fluorescence and air-Cherenkov techniques, where the radio technique offers the advantage of a significantly higher duty-cycle. Finally, the hyperbolic wavefront can be used to reconstruct the shower geometry more accurately, which potentially allows a better reconstruction of all other shower parameters, too.« less

The wavefront of the radio signal emitted by cosmic ray air showers

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schoo, S.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2014-09-01

Analyzing measurements of the LOPES antenna array together with corresponding CoREAS simulations for more than 300 measured events with energy above 1017 eV and zenith angles smaller than 45o, we find that the radio wavefront of cosmic-ray air showers is of approximately hyperbolic shape. The simulations predict a slightly steeper wavefront towards East than towards West, but this asymmetry is negligible against the measurement uncertainties of LOPES. At axis distances gtrsim 50 m, the wavefront can be approximated by a simple cone. According to the simulations, the cone angle is clearly correlated with the shower maximum. Thus, we confirm earlier predictions that arrival time measurements can be used to study the longitudinal shower development, but now using a realistic wavefront. Moreover, we show that the hyperbolic wavefront is compatible with our measurement, and we present several experimental indications that the cone angle is indeed sensitive to the shower development. Consequently, the wavefront can be used to statistically study the primary composition of ultra-high energy cosmic rays. At LOPES, the experimentally achieved precision for the shower maximum is limited by measurement uncertainties to approximately 140 g/c 2. But the simulations indicate that under better conditions this method might yield an accuracy for the atmospheric depth of the shower maximum, Xmax, better than 30 g/c 2. This would be competitive with the established air-fluorescence and air-Cherenkov techniques, where the radio technique offers the advantage of a significantly higher duty-cycle. Finally, the hyperbolic wavefront can be used to reconstruct the shower geometry more accurately, which potentially allows a better reconstruction of all other shower parameters, too.

Implementation and on-sky results of an optimal wavefront controller for the MMT NGS adaptive optics system

NASA Astrophysics Data System (ADS)

Powell, Keith B.; Vaitheeswaran, Vidhya

2010-07-01

The MMT observatory has recently implemented and tested an optimal wavefront controller for the NGS adaptive optics system. Open loop atmospheric data collected at the telescope is used as the input to a MATLAB based analytical model. The model uses nonlinear constrained minimization to determine controller gains and optimize the system performance. The real-time controller performing the adaptive optics close loop operation is implemented on a dedicated high performance PC based quad core server. The controller algorithm is written in C and uses the GNU scientific library for linear algebra. Tests at the MMT confirmed the optimal controller significantly reduced the residual RMS wavefront compared with the previous controller. Significant reductions in image FWHM and increased peak intensities were obtained in J, H and K-bands. The optimal PID controller is now operating as the baseline wavefront controller for the MMT NGS-AO system.

Status of Technology Development to enable Large Stable UVOIR Space Telescopes

NASA Astrophysics Data System (ADS)

Stahl, H. Philip; MSFC AMTD Team

2017-01-01

NASA MSFC has two funded Strategic Astrophysics Technology projects to develop technology for potential future large missions: AMTD and PTC. The Advanced Mirror Technology Development (AMTD) project is developing technology to make mechanically stable mirrors for a 4-meter or larger UVOIR space telescope. AMTD is demonstrating this technology by making a 1.5 meter diameter x 200 mm thick ULE(C) mirror that is 1/3rd scale of a full size 4-m mirror. AMTD is characterizing the mechanical and thermal performance of this mirror and of a 1.2-meter Zerodur(R) mirror to validate integrate modeling tools. Additionally, AMTD has developed integrated modeling tools which are being used to evaluate primary mirror systems for a potential Habitable Exoplanet Mission and analyzed the interaction between optical telescope wavefront stability and coronagraph contrast leakage. Predictive Thermal Control (PTC) project is developing technology to enable high stability thermal wavefront performance by using integrated modeling tools to predict and actively control the thermal environment of a 4-m or larger UVOIR space telescope.

Wavefront error sensing for LDR

NASA Technical Reports Server (NTRS)

Tubbs, Eldred F.; Glavich, T. A.

1988-01-01

Wavefront sensing is a significant aspect of the LDR control problem and requires attention at an early stage of the control system definition and design. A combination of a Hartmann test for wavefront slope measurement and an interference test for piston errors of the segments was examined and is presented as a point of departure for further discussion. The assumption is made that the wavefront sensor will be used for initial alignment and periodic alignment checks but that it will not be used during scientific observations. The Hartmann test and the interferometric test are briefly examined.

End-To-End performance test of the LINC-NIRVANA Wavefront-Sensor system.

NASA Astrophysics Data System (ADS)

Berwein, Juergen; Bertram, Thomas; Conrad, Al; Briegel, Florian; Kittmann, Frank; Zhang, Xiangyu; Mohr, Lars

2011-09-01

LINC-NIRVANA is an imaging Fizeau interferometer, for use in near infrared wavelengths, being built for the Large Binocular Telescope. Multi-conjugate adaptive optics (MCAO) increases the sky coverage and the field of view over which diffraction limited images can be obtained. For its MCAO implementation, Linc-Nirvana utilizes four total wavefront sensors; each of the two beams is corrected by both a ground-layer wavefront sensor (GWS) and a high-layer wavefront sensor (HWS). The GWS controls the adaptive secondary deformable mirror (DM), which is based on an DSP slope computing unit. Whereas the HWS controls an internal DM via computations provided by an off-the-shelf multi-core Linux system. Using wavefront sensor data collected from a prior lab experiment, we have shown via simulation that the Linux based system is sufficient to operate at 1kHz, with jitter well below the needs of the final system. Based on that setup we tested the end-to-end performance and latency through all parts of the system which includes the camera, the wavefront controller, and the deformable mirror. We will present our loop control structure and the results of those performance tests.

Development of a scalable generic platform for adaptive optics real time control

NASA Astrophysics Data System (ADS)

Surendran, Avinash; Burse, Mahesh P.; Ramaprakash, A. N.; Parihar, Padmakar

2015-06-01

The main objective of the present project is to explore the viability of an adaptive optics control system based exclusively on Field Programmable Gate Arrays (FPGAs), making strong use of their parallel processing capability. In an Adaptive Optics (AO) system, the generation of the Deformable Mirror (DM) control voltages from the Wavefront Sensor (WFS) measurements is usually through the multiplication of the wavefront slopes with a predetermined reconstructor matrix. The ability to access several hundred hard multipliers and memories concurrently in an FPGA allows performance far beyond that of a modern CPU or GPU for tasks with a well-defined structure such as Adaptive Optics control. The target of the current project is to generate a signal for a real time wavefront correction, from the signals coming from a Wavefront Sensor, wherein the system would be flexible to accommodate all the current Wavefront Sensing techniques and also the different methods which are used for wavefront compensation. The system should also accommodate for different data transmission protocols (like Ethernet, USB, IEEE 1394 etc.) for transmitting data to and from the FPGA device, thus providing a more flexible platform for Adaptive Optics control. Preliminary simulation results for the formulation of the platform, and a design of a fully scalable slope computer is presented.

New Objective Refraction Metric Based on Sphere Fitting to the Wavefront

PubMed Central

Martínez-Finkelshtein, Andreí

2017-01-01

Purpose To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. Methods A sphere is fitted to the ocular wavefront at the center and at a variable distance, t. The optimal fitting distance, topt, is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r0, and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. Results For pupil radii r0 ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r0 > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size. PMID:29104804

New Objective Refraction Metric Based on Sphere Fitting to the Wavefront.

PubMed

Jaskulski, Mateusz; Martínez-Finkelshtein, Andreí; López-Gil, Norberto

2017-01-01

To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. A sphere is fitted to the ocular wavefront at the center and at a variable distance, t . The optimal fitting distance, t opt , is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r 0 , and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. For pupil radii r 0 ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r 0 > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size.

Adaptive wavefront shaping for controlling nonlinear multimode interactions in optical fibres

NASA Astrophysics Data System (ADS)

Tzang, Omer; Caravaca-Aguirre, Antonio M.; Wagner, Kelvin; Piestun, Rafael

2018-06-01

Recent progress in wavefront shaping has enabled control of light propagation inside linear media to focus and image through scattering objects. In particular, light propagation in multimode fibres comprises complex intermodal interactions and rich spatiotemporal dynamics. Control of physical phenomena in multimode fibres and its applications are in their infancy, opening opportunities to take advantage of complex nonlinear modal dynamics. Here, we demonstrate a wavefront shaping approach for controlling nonlinear phenomena in multimode fibres. Using a spatial light modulator at the fibre input, real-time spectral feedback and a genetic algorithm optimization, we control a highly nonlinear multimode stimulated Raman scattering cascade and its interplay with four-wave mixing via a flexible implicit control on the superposition of modes coupled into the fibre. We show versatile spectrum manipulations including shifts, suppression, and enhancement of Stokes and anti-Stokes peaks. These demonstrations illustrate the power of wavefront shaping to control and optimize nonlinear wave propagation.

Closing the contrast gap between testbed and model prediction with WFIRST-CGI shaped pupil coronagraph

NASA Astrophysics Data System (ADS)

Zhou, Hanying; Nemati, Bijan; Krist, John; Cady, Eric; Prada, Camilo M.; Kern, Brian; Poberezhskiy, Ilya

2016-07-01

JPL has recently passed an important milestone in its technology development for a proposed NASA WFIRST mission coronagraph: demonstration of better than 1x10-8 contrast over broad bandwidth (10%) on both shaped pupil coronagraph (SPC) and hybrid Lyot coronagraph (HLC) testbeds with the WFIRST obscuration pattern. Challenges remain, however, in the technology readiness for the proposed mission. One is the discrepancies between the achieved contrasts on the testbeds and their corresponding model predictions. A series of testbed diagnoses and modeling activities were planned and carried out on the SPC testbed in order to close the gap. A very useful tool we developed was a derived "measured" testbed wavefront control Jacobian matrix that could be compared with the model-predicted "control" version that was used to generate the high contrast dark hole region in the image plane. The difference between these two is an estimate of the error in the control Jacobian. When the control matrix, which includes both amplitude and phase, was modified to reproduce the error, the simulated performance closely matched the SPC testbed behavior in both contrast floor and contrast convergence speed. This is a step closer toward model validation for high contrast coronagraphs. Further Jacobian analysis and modeling provided clues to the possible sources for the mismatch: DM misregistration and testbed optical wavefront error (WFE) and the deformable mirror (DM) setting for correcting this WFE. These analyses suggested that a high contrast coronagraph has a tight tolerance in the accuracy of its control Jacobian. Modifications to both testbed control model as well as prediction model are being implemented, and future works are discussed.

Integrated Modeling Activities for the James Webb Space Telescope: Optical Jitter Analysis

NASA Technical Reports Server (NTRS)

Hyde, T. Tupper; Ha, Kong Q.; Johnston, John D.; Howard, Joseph M.; Mosier, Gary E.

2004-01-01

This is a continuation of a series of papers on the integrated modeling activities for the James Webb Space Telescope(JWST). Starting with the linear optical model discussed in part one, and using the optical sensitivities developed in part two, we now assess the optical image motion and wavefront errors from the structural dynamics. This is often referred to as "jitter: analysis. The optical model is combined with the structural model and the control models to create a linear structural/optical/control model. The largest jitter is due to spacecraft reaction wheel assembly disturbances which are harmonic in nature and will excite spacecraft and telescope structural. The structural/optic response causes image quality degradation due to image motion (centroid error) as well as dynamic wavefront error. Jitter analysis results are used to predict imaging performance, improve the structural design, and evaluate the operational impact of the disturbance sources.

Hybrid Large Eddy Simulation / Reynolds Averaged Navier-Stokes Modeling in Directed Energy Applications

NASA Astrophysics Data System (ADS)

Zilberter, Ilya Alexandrovich

In this work, a hybrid Large Eddy Simulation / Reynolds-Averaged Navier Stokes (LES/RANS) turbulence model is applied to simulate two flows relevant to directed energy applications. The flow solver blends the Menter Baseline turbulence closure near solid boundaries with a Lenormand-type subgrid model in the free-stream with a blending function that employs the ratio of estimated inner and outer turbulent length scales. A Mach 2.2 mixing nozzle/diffuser system representative of a gas laser is simulated under a range of exit pressures to assess the ability of the model to predict the dynamics of the shock train. The simulation captures the location of the shock train responsible for pressure recovery but under-predicts the rate of pressure increase. Predicted turbulence production at the wall is found to be highly sensitive to the behavior of the RANS turbulence model. A Mach 2.3, high-Reynolds number, three-dimensional cavity flow is also simulated in order to compute the wavefront aberrations of an optical beam passing thorough the cavity. The cavity geometry is modeled using an immersed boundary method, and an auxiliary flat plate simulation is performed to replicate the effects of the wind-tunnel boundary layer on the computed optical path difference. Pressure spectra extracted on the cavity walls agree with empirical predictions based on Rossiter's formula. Proper orthogonal modes of the wavefront aberrations in a beam originating from the cavity center agree well with experimental data despite uncertainty about in flow turbulence levels and boundary layer thicknesses over the wind tunnel window. Dynamic mode decomposition of a planar wavefront spanning the cavity reveals that wavefront distortions are driven by shear layer oscillations at the Rossiter frequencies; these disturbances create eddy shocklets that propagate into the free-stream, creating additional optical wavefront distortion.

Wavefront sensors for the active control of earth observation optical instruments

NASA Astrophysics Data System (ADS)

Velluet, Marie-Thérèse; Michau, Vincent; Rousset, Gérard

2018-04-01

This paper, "Wavefront sensors for the active control of earth observation optical instruments," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.

The PALM-3000 high-order adaptive optics system for Palomar Observatory

NASA Astrophysics Data System (ADS)

Bouchez, Antonin H.; Dekany, Richard G.; Angione, John R.; Baranec, Christoph; Britton, Matthew C.; Bui, Khanh; Burruss, Rick S.; Cromer, John L.; Guiwits, Stephen R.; Henning, John R.; Hickey, Jeff; McKenna, Daniel L.; Moore, Anna M.; Roberts, Jennifer E.; Trinh, Thang Q.; Troy, Mitchell; Truong, Tuan N.; Velur, Viswa

2008-07-01

Deployed as a multi-user shared facility on the 5.1 meter Hale Telescope at Palomar Observatory, the PALM-3000 highorder upgrade to the successful Palomar Adaptive Optics System will deliver extreme AO correction in the near-infrared, and diffraction-limited images down to visible wavelengths, using both natural and sodium laser guide stars. Wavefront control will be provided by two deformable mirrors, a 3368 active actuator woofer and 349 active actuator tweeter, controlled at up to 3 kHz using an innovative wavefront processor based on a cluster of 17 graphics processing units. A Shack-Hartmann wavefront sensor with selectable pupil sampling will provide high-order wavefront sensing, while an infrared tip/tilt sensor and visible truth wavefront sensor will provide low-order LGS control. Four back-end instruments are planned at first light: the PHARO near-infrared camera/spectrograph, the SWIFT visible light integral field spectrograph, Project 1640, a near-infrared coronagraphic integral field spectrograph, and 888Cam, a high-resolution visible light imager.

Amplitude and phase beam characterization using a two-dimensional wavefront sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neal, D.R.; Alford, W.J.; Gruetzner, J.K.

1996-09-01

We have developed a two-dimensional Shack-Hartman wavefront sensor that uses binary optic lenslet arrays to directly measure the wavefront slope (phase gradient) and amplitude of the laser beam. This sensor uses an array of lenslets that dissects the beam into a number of samples. The focal spot location of each of these lenslets (measured by a CCD camera) is related to the incoming wavefront slope over the lenslet. By integrating these measurements over the laser aperture, the wavefront or phase distribution can be determined. Since the power focused by each lenslet is also easily determined, this allows a complete measurementmore » of the intensity and phase distribution of the laser beam. Furthermore, all the information is obtained in a single measurement. Knowing the complete scalar field of the beam allows the detailed prediction of the actual beam`s characteristics along its propagation path. In particular, the space- beamwidth product M{sup 2}, can be obtained in a single measurement. The intensity and phase information can be used in concert with information about other elements in the optical train to predict the beam size, shape, phase and other characteristics anywhere in the optical train. We present preliminary measurements of an Ar{sup +} laser beam and associated M{sup 2} calculations.« less

Wavefront sensing and adaptive control in phased array of fiber collimators

NASA Astrophysics Data System (ADS)

Lachinova, Svetlana L.; Vorontsov, Mikhail A.

2011-03-01

A new wavefront control approach for mitigation of atmospheric turbulence-induced wavefront phase aberrations in coherent fiber-array-based laser beam projection systems is introduced and analyzed. This approach is based on integration of wavefront sensing capabilities directly into the fiber-array transmitter aperture. In the coherent fiber array considered, we assume that each fiber collimator (subaperture) of the array is capable of precompensation of local (onsubaperture) wavefront phase tip and tilt aberrations using controllable rapid displacement of the tip of the delivery fiber at the collimating lens focal plane. In the technique proposed, this tip and tilt phase aberration control is based on maximization of the optical power received through the same fiber collimator using the stochastic parallel gradient descent (SPGD) technique. The coordinates of the fiber tip after the local tip and tilt aberrations are mitigated correspond to the coordinates of the focal-spot centroid of the optical wave backscattered off the target. Similar to a conventional Shack-Hartmann wavefront sensor, phase function over the entire fiber-array aperture can then be retrieved using the coordinates obtained. The piston phases that are required for coherent combining (phase locking) of the outgoing beams at the target plane can be further calculated from the reconstructed wavefront phase. Results of analysis and numerical simulations are presented. Performance of adaptive precompensation of phase aberrations in this laser beam projection system type is compared for various system configurations characterized by the number of fiber collimators and atmospheric turbulence conditions. The wavefront control concept presented can be effectively applied for long-range laser beam projection scenarios for which the time delay related with the double-pass laser beam propagation to the target and back is compared or even exceeds the characteristic time of the atmospheric turbulence change - scenarios when conventional target-in-the-loop phase-locking techniques fail.

Wavefront correction by target-phase-locking technology in a 500 TW laser facility

NASA Astrophysics Data System (ADS)

Wang, D. E.; Dai, W. J.; Zhou, K. N.; Su, J. Q.; Xue, Q.; Yuan, Q.; Zhang, X.; Deng, X. W.; Yang, Y.; Wang, Y. C.; Xie, N.; Sun, L.; Hu, D. X.; Zhu, Q. H.

2017-03-01

We demonstrate a novel approach termed target-phase-locking that could improve the entire beam wavefront quality of a 500 TW Nd3+:phosphate glass laser facility. The thermal and static wavefront from front-end to target is corrected by using one deformable mirror that receives feedback from both the focal-spot sensor and wavefront sensor, and only the main laser of the laser system is employed in the correction process, with auxiliary calibration light no longer necessary. As a result, a static focal spot with full width at half maximum of 8.87  ×  5.74 µm is achieved, the thermal wavefront induced by flash-lamp-pumped Nd3+:phosphate glass is compensated with PV from 3.54-0.43 µm, and a dynamic focal spot with intensity exceeding 1020 W cm-2 is precisely predicted at the target with such an approach.

Statistical analysis of wavefront fluctuations from measurements of a wave-front sensor

NASA Astrophysics Data System (ADS)

Botygina, N. N.; Emaleev, O. N.; Konyaev, P. A.; Lukin, V. P.

2017-11-01

Measurements of the wave front aberrations at the input aperture of the Big Solar Vacuum Telescope (LSVT) were carried out by a wave-front sensor (WFS) of an adaptive optical system when the controlled deformable mirror was replaced by a plane one.

Sub-pixel spatial resolution wavefront phase imaging

NASA Technical Reports Server (NTRS)

Stahl, H. Philip (Inventor); Mooney, James T. (Inventor)

2012-01-01

A phase imaging method for an optical wavefront acquires a plurality of phase images of the optical wavefront using a phase imager. Each phase image is unique and is shifted with respect to another of the phase images by a known/controlled amount that is less than the size of the phase imager's pixels. The phase images are then combined to generate a single high-spatial resolution phase image of the optical wavefront.

Correction of large amplitude wavefront aberrations

NASA Astrophysics Data System (ADS)

Cornelissen, S. A.; Bierden, P. A.; Bifano, T. G.; Webb, R. H.; Burns, S.; Pappas, S.

2005-12-01

Recently, a number of research groups around the world have developed ophthalmic instruments capable of in vivo diffraction limited imaging of the human retina. Adaptive optics was used in these systems to compensate for the optical aberrations of the eye and provide high contrast, high resolution images. Such compensation uses a wavefront sensor and a wavefront corrector (usually a deformable mirror) coordinated in a closed- loop control system that continuously works to counteract aberrations. While those experiments produced promising results, the deformable mirrors have had insufficient range of motion to permit full correction of the large amplitude aberrations of the eye expected in a normal population of human subjects. Other retinal imaging systems developed to date with MEMS (micro-electromechanical systems) DMs suffer similar limitations. This paper describes the design, manufacture and testing of a 6um stroke polysilicon surface micromachined deformable mirror that, coupled with an new optical method to double the effective stroke of the MEMS-DM, will permit diffraction-limited retinal imaging through dilated pupils in at least 90% of the human population. A novel optical design using spherical mirrors provides a double pass of the wavefront over the deformable mirror such that a 6um mirror displacement results in 12um of wavefront compensation which could correct for 24um of wavefront error. Details of this design are discussed. Testing of the effective wavefront modification was performed using a commercial wavefront sensor. Results are presented demonstrating improvement in the amplitude of wavefront control using an existing high degree of freedom MEMS deformable mirror.

Wavefront Control Testbed (WCT) Experiment Results

NASA Technical Reports Server (NTRS)

Burns, Laura A.; Basinger, Scott A.; Campion, Scott D.; Faust, Jessica A.; Feinberg, Lee D.; Hayden, William L.; Lowman, Andrew E.; Ohara, Catherine M.; Petrone, Peter P., III

2004-01-01

The Wavefront Control Testbed (WCT) was created to develop and test wavefront sensing and control algorithms and software for the segmented James Webb Space Telescope (JWST). Last year, we changed the system configuration from three sparse aperture segments to a filled aperture with three pie shaped segments. With this upgrade we have performed experiments on fine phasing with line-of-sight and segment-to-segment jitter, dispersed fringe visibility and grism angle;. high dynamic range tilt sensing; coarse phasing with large aberrations, and sampled sub-aperture testing. This paper reviews the results of these experiments.

Wavefront correction and high-resolution in vivo OCT imaging with an objective integrated multi-actuator adaptive lens.

PubMed

Bonora, Stefano; Jian, Yifan; Zhang, Pengfei; Zam, Azhar; Pugh, Edward N; Zawadzki, Robert J; Sarunic, Marinko V

2015-08-24

Adaptive optics is rapidly transforming microscopy and high-resolution ophthalmic imaging. The adaptive elements commonly used to control optical wavefronts are liquid crystal spatial light modulators and deformable mirrors. We introduce a novel Multi-actuator Adaptive Lens that can correct aberrations to high order, and which has the potential to increase the spread of adaptive optics to many new applications by simplifying its integration with existing systems. Our method combines an adaptive lens with an imaged-based optimization control that allows the correction of images to the diffraction limit, and provides a reduction of hardware complexity with respect to existing state-of-the-art adaptive optics systems. The Multi-actuator Adaptive Lens design that we present can correct wavefront aberrations up to the 4th order of the Zernike polynomial characterization. The performance of the Multi-actuator Adaptive Lens is demonstrated in a wide field microscope, using a Shack-Hartmann wavefront sensor for closed loop control. The Multi-actuator Adaptive Lens and image-based wavefront-sensorless control were also integrated into the objective of a Fourier Domain Optical Coherence Tomography system for in vivo imaging of mouse retinal structures. The experimental results demonstrate that the insertion of the Multi-actuator Objective Lens can generate arbitrary wavefronts to correct aberrations down to the diffraction limit, and can be easily integrated into optical systems to improve the quality of aberrated images.

Complete wavefront and polarization control for ultrashort-pulse laser microprocessing.

PubMed

Allegre, O J; Jin, Y; Perrie, W; Ouyang, J; Fearon, E; Edwardson, S P; Dearden, G

2013-09-09

We report on new developments in wavefront and polarization control for ultrashort-pulse laser microprocessing. We use two Spatial Light Modulators in combination to structure the optical fields of a picosecond-pulse laser beam, producing vortex wavefronts and radial or azimuthal polarization states. We also carry out the first demonstration of multiple first-order beams with vortex wavefronts and radial or azimuthal polarization states, produced using Computer Generated Holograms. The beams produced are used to nano-structure a highly polished metal surface. Laser Induced Periodic Surface Structures are observed and used to directly verify the state of polarization in the focal plane and help to characterize the optical properties of the setup.

Digital pyramid wavefront sensor with tunable modulation.

PubMed

Akondi, Vyas; Castillo, Sara; Vohnsen, Brian

2013-07-29

The pyramid wavefront sensor is known for its high sensitivity and dynamic range that can be tuned by mechanically altering its modulation amplitude. Here, a novel modulating digital scheme employing a reflecting phase only spatial light modulator is demonstrated. The use of the modulator allows an easy reconfigurable pyramid with digital control of the apex angle and modulation geometry without the need of any mechanically moving parts. Aberrations introduced by a 140-actuator deformable mirror were simultaneously sensed with the help of a commercial Hartmann-Shack wavefront sensor. The wavefronts reconstructed using the digital pyramid wavefront sensor matched very closely with those sensed by the Hartmann-Shack. It is noted that a tunable modulation is necessary to operate the wavefront sensor in the linear regime and to accurately sense aberrations. Through simulations, it is shown that the wavefront sensor can be extended to astronomical applications as well. This novel digital pyramid wavefront sensor has the potential to become an attractive option in both open and closed loop adaptive optics systems.

Control algorithms and applications of the wavefront sensorless adaptive optics

NASA Astrophysics Data System (ADS)

Ma, Liang; Wang, Bin; Zhou, Yuanshen; Yang, Huizhen

2017-10-01

Compared with the conventional adaptive optics (AO) system, the wavefront sensorless (WFSless) AO system need not to measure the wavefront and reconstruct it. It is simpler than the conventional AO in system architecture and can be applied to the complex conditions. Based on the analysis of principle and system model of the WFSless AO system, wavefront correction methods of the WFSless AO system were divided into two categories: model-free-based and model-based control algorithms. The WFSless AO system based on model-free-based control algorithms commonly considers the performance metric as a function of the control parameters and then uses certain control algorithm to improve the performance metric. The model-based control algorithms include modal control algorithms, nonlinear control algorithms and control algorithms based on geometrical optics. Based on the brief description of above typical control algorithms, hybrid methods combining the model-free-based control algorithm with the model-based control algorithm were generalized. Additionally, characteristics of various control algorithms were compared and analyzed. We also discussed the extensive applications of WFSless AO system in free space optical communication (FSO), retinal imaging in the human eye, confocal microscope, coherent beam combination (CBC) techniques and extended objects.

Closed-loop focal plane wavefront control with the SCExAO instrument

NASA Astrophysics Data System (ADS)

Martinache, Frantz; Jovanovic, Nemanja; Guyon, Olivier

2016-09-01

Aims: This article describes the implementation of a focal plane based wavefront control loop on the high-contrast imaging instrument SCExAO (Subaru Coronagraphic Extreme Adaptive Optics). The sensor relies on the Fourier analysis of conventional focal-plane images acquired after an asymmetric mask is introduced in the pupil of the instrument. Methods: This absolute sensor is used here in a closed-loop to compensate for the non-common path errors that normally affects any imaging system relying on an upstream adaptive optics system.This specific implementation was used to control low-order modes corresponding to eight zernike modes (from focus to spherical). Results: This loop was successfully run on-sky at the Subaru Telescope and is used to offset the SCExAO deformable mirror shape used as a zero-point by the high-order wavefront sensor. The paper details the range of errors this wavefront-sensing approach can operate within and explores the impact of saturation of the data and how it can be bypassed, at a cost in performance. Conclusions: Beyond this application, because of its low hardware impact, the asymmetric pupil Fourier wavefront sensor (APF-WFS) can easily be ported in a wide variety of wavefront sensing contexts, for ground- as well space-borne telescopes, and for telescope pupils that can be continuous, segmented or even sparse. The technique is powerful because it measures the wavefront where it really matters, at the level of the science detector.

Solar adaptive optics with the DKIST: status report

NASA Astrophysics Data System (ADS)

Johnson, Luke C.; Cummings, Keith; Drobilek, Mark; Gregory, Scott; Hegwer, Steve; Johansson, Erik; Marino, Jose; Richards, Kit; Rimmele, Thomas; Sekulic, Predrag; Wöger, Friedrich

2014-08-01

The DKIST wavefront correction system will be an integral part of the telescope, providing active alignment control, wavefront correction, and jitter compensation to all DKIST instruments. The wavefront correction system will operate in four observing modes, diffraction-limited, seeing-limited on-disk, seeing-limited coronal, and limb occulting with image stabilization. Wavefront correction for DKIST includes two major components: active optics to correct low-order wavefront and alignment errors, and adaptive optics to correct wavefront errors and high-frequency jitter caused by atmospheric turbulence. The adaptive optics system is built around a fast tip-tilt mirror and a 1600 actuator deformable mirror, both of which are controlled by an FPGA-based real-time system running at 2 kHz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r0 = 20 cm). We present the current status of the DKIST high-order adaptive optics, focusing on system design, hardware procurements, and error budget management.

Experimental study of an adaptive CFRC reflector for high order wave-front error correction

NASA Astrophysics Data System (ADS)

Lan, Lan; Fang, Houfei; Wu, Ke; Jiang, Shuidong; Zhou, Yang

2018-03-01

The recent radio frequency communication system developments are generating the need for creating space antennas with lightweight and high precision. The carbon fiber reinforced composite (CFRC) materials have been used to manufacture the high precision reflector. The wave-front errors caused by fabrication and on-orbit distortion are inevitable. The adaptive CFRC reflector has received much attention to do the wave-front error correction. Due to uneven stress distribution that is introduced by actuation force and fabrication, the high order wave-front errors such as print-through error is found on the reflector surface. However, the adaptive CFRC reflector with PZT actuators basically has no control authority over the high order wave-front errors. A new design architecture assembled secondary ribs at the weak triangular surfaces is presented in this paper. The virtual experimental study of the new adaptive CFRC reflector has conducted. The controllability of the original adaptive CFRC reflector and the new adaptive CFRC reflector with secondary ribs are investigated. The virtual experimental investigation shows that the new adaptive CFRC reflector is feasible and efficient to diminish the high order wave-front error.

Optimal wavefront estimation of incoherent sources

NASA Astrophysics Data System (ADS)

Riggs, A. J. Eldorado; Kasdin, N. Jeremy; Groff, Tyler

2014-08-01

Direct imaging is in general necessary to characterize exoplanets and disks. A coronagraph is an instrument used to create a dim (high-contrast) region in a star's PSF where faint companions can be detected. All coronagraphic high-contrast imaging systems use one or more deformable mirrors (DMs) to correct quasi-static aberrations and recover contrast in the focal plane. Simulations show that existing wavefront control algorithms can correct for diffracted starlight in just a few iterations, but in practice tens or hundreds of control iterations are needed to achieve high contrast. The discrepancy largely arises from the fact that simulations have perfect knowledge of the wavefront and DM actuation. Thus, wavefront correction algorithms are currently limited by the quality and speed of wavefront estimates. Exposures in space will take orders of magnitude more time than any calculations, so a nonlinear estimation method that needs fewer images but more computational time would be advantageous. In addition, current wavefront correction routines seek only to reduce diffracted starlight. Here we present nonlinear estimation algorithms that include optimal estimation of sources incoherent with a star such as exoplanets and debris disks.

Thirty Meter Telescope (TMT) Narrow Field Infrared Adaptive Optics System (NFIRAOS) real-time controller preliminary architecture

NASA Astrophysics Data System (ADS)

Kerley, Dan; Smith, Malcolm; Dunn, Jennifer; Herriot, Glen; Véran, Jean-Pierre; Boyer, Corinne; Ellerbroek, Brent; Gilles, Luc; Wang, Lianqi

2016-08-01

The Narrow Field Infrared Adaptive Optics System (NFIRAOS) is the first light Adaptive Optics (AO) system for the Thirty Meter Telescope (TMT). A critical component of NFIRAOS is the Real-Time Controller (RTC) subsystem which provides real-time wavefront correction by processing wavefront information to compute Deformable Mirror (DM) and Tip/Tilt Stage (TTS) commands. The National Research Council of Canada - Herzberg (NRC-H), in conjunction with TMT, has developed a preliminary design for the NFIRAOS RTC. The preliminary architecture for the RTC is comprised of several Linux-based servers. These servers are assigned various roles including: the High-Order Processing (HOP) servers, the Wavefront Corrector Controller (WCC) server, the Telemetry Engineering Display (TED) server, the Persistent Telemetry Storage (PTS) server, and additional testing and spare servers. There are up to six HOP servers that accept high-order wavefront pixels, and perform parallelized pixel processing and wavefront reconstruction to produce wavefront corrector error vectors. The WCC server performs low-order mode processing, and synchronizes and aggregates the high-order wavefront corrector error vectors from the HOP servers to generate wavefront corrector commands. The Telemetry Engineering Display (TED) server is the RTC interface to TMT and other subsystems. The TED server receives all external commands and dispatches them to the rest of the RTC servers and is responsible for aggregating several offloading and telemetry values that are reported to other subsystems within NFIRAOS and TMT. The TED server also provides the engineering GUIs and real-time displays. The Persistent Telemetry Storage (PTS) server contains fault tolerant data storage that receives and stores telemetry data, including data for Point-Spread Function Reconstruction (PSFR).

Compact illumination optic with three freeform surfaces for improved beam control.

PubMed

Sorgato, Simone; Mohedano, Rubén; Chaves, Julio; Hernández, Maikel; Blen, José; Grabovičkić, Dejan; Benítez, Pablo; Miñano, Juan Carlos; Thienpont, Hugo; Duerr, Fabian

2017-11-27

Multi-chip and large size LEDs dominate the lighting market in developed countries these days. Nevertheless, a general optical design method to create prescribed intensity patterns for this type of extended sources does not exist. We present a design strategy in which the source and the target pattern are described by means of "edge wavefronts" of the system. The goal is then finding an optic coupling these wavefronts, which in the current work is a monolithic part comprising up to three freeform surfaces calculated with the simultaneous multiple surface (SMS) method. The resulting optic fully controls, for the first time, three freeform wavefronts, one more than previous SMS designs. Simulations with extended LEDs demonstrate improved intensity tailoring capabilities, confirming the effectiveness of our method and suggesting that enhanced performance features can be achieved by controlling additional wavefronts.

Spoof surface plasmon polaritons excitation and wavefront control by Pancharatnam–Berry phase manipulating metasurface

NASA Astrophysics Data System (ADS)

Meng, Yueyu; Ma, Hua; Li, Yongfeng; Feng, Mingde; Wang, Jiafu; Li, Zhiqiang; Qu, Shaobo

2018-05-01

Realizing fine control of surface plasmon polaritons (SPPs) and spoof surface plasmon polaritons (SSPPs) is highly desired in many integrated photonic and microwave applications, but the flexibility to control the wavefront of SPPs and SSPPs still need addressing. In this paper, a Pancharatnam–Berry (PB) phase manipulating metasurface (PMM) was designed to achieve SSPPs excitation and wavefront control. Under circular polarization (CP) incidence, simply by designing the rotation angle of the unit cells the reflection phase spatial distribution can be manipulated. By means of different phase profiles on the 2D unit cells array, the SSPPs can be excited with various wavefront shapes, without the need of special excitation structure pattern. Meanwhile, a plasmonic metal is also designed to support SSPPs with both TE and TM polarizations, which can efficiently guide out the energies from the input CP waves. As a proof of concept, a PB PMM composed of N-shape metallic structure was designed. Through designing the rotation of the unit cells, two typical phase profiles were designed to excite SSPPs in arbitrary slant direction or focusing. This scheme could be used to achieve SSPPs excitation with many other wavefront shapes, and would also enable promising applications in other spectra.

High-contrast imager for Complex Aperture Telescopes (HiCAT). 4. Status and wavefront control development

NASA Astrophysics Data System (ADS)

Leboulleux, Lucie; N'Diaye, Mamadou; Riggs, A. J. E.; Egron, Sylvain; Mazoyer, Johan; Pueyo, Laurent; Choquet, Elodie; Perrin, Marshall D.; Kasdin, Jeremy; Sauvage, Jean-François; Fusco, Thierry; Soummer, Rémi

2016-07-01

Segmented telescopes are a possible approach to enable large-aperture space telescopes for the direct imaging and spectroscopy of habitable worlds. However, the increased complexity of their aperture geometry, due to their central obstruction, support structures and segment gaps, makes high-contrast imaging very challenging. The High-contrast imager for Complex Aperture Telescopes (HiCAT) was designed to study and develop solutions for such telescope pupils using wavefront control and starlight suppression. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures (e.g. the Wide Field Infrared Survey Telescope [WFIRST]), up to on-axis segmented telescopes e.g. including various concepts for a Large UV, Optical, IR telescope (LUVOIR), such as the High Definition Space Telescope (HDST). We completed optical alignment in the summer of 2014 and a first deformable mirror was successfully integrated in the testbed, with a total wavefront error of 13nm RMS over a 18mm diameter circular pupil in open loop. HiCAT will also be provided with a segmented mirror conjugated with a shaped pupil representing the HDST configuration, to directly study wavefront control in the presence of segment gaps, central obstruction and spider. We recently applied a focal plane wavefront control method combined with a classical Lyot coronagraph on HiCAT, and we found limitations on contrast performance due to vibration effect. In this communication, we analyze this instability and study its impact on the performance of wavefront control algorithms. We present our Speckle Nulling code to control and correct for wavefront errors both in simulation mode and on testbed mode. This routine is first tested in simulation mode without instability to validate our code. We then add simulated vibrations to study the degradation of contrast performance in the presence of these effects.

Wavefront Control Toolbox for James Webb Space Telescope Testbed

NASA Technical Reports Server (NTRS)

Shiri, Ron; Aronstein, David L.; Smith, Jeffery Scott; Dean, Bruce H.; Sabatke, Erin

2007-01-01

We have developed a Matlab toolbox for wavefront control of optical systems. We have applied this toolbox to the optical models of James Webb Space Telescope (JWST) in general and to the JWST Testbed Telescope (TBT) in particular, implementing both unconstrained and constrained wavefront optimization to correct for possible misalignments present on the segmented primary mirror or the monolithic secondary mirror. The optical models implemented in Zemax optical design program and information is exchanged between Matlab and Zemax via the Dynamic Data Exchange (DDE) interface. The model configuration is managed using the XML protocol. The optimization algorithm uses influence functions for each adjustable degree of freedom of the optical mode. The iterative and non-iterative algorithms have been developed to converge to a local minimum of the root-mean-square (rms) of wavefront error using singular value decomposition technique of the control matrix of influence functions. The toolkit is highly modular and allows the user to choose control strategies for the degrees of freedom to be adjusted on a given iteration and wavefront convergence criterion. As the influence functions are nonlinear over the control parameter space, the toolkit also allows for trade-offs between frequency of updating the local influence functions and execution speed. The functionality of the toolbox and the validity of the underlying algorithms have been verified through extensive simulations.

Non-invasive three-dimension control of light between turbid layers using a surface quasi-point light source for precorrection.

PubMed

Qiao, Mu; Liu, Honglin; Pang, Guanghui; Han, Shensheng

2017-08-29

Manipulating light non-invasively through inhomogeneous media is an attractive goal in many disciplines. Wavefront shaping and optical phase conjugation can focus light to a point. Transmission matrix method can control light on multiple output modes simultaneously. Here we report a non-invasive approach which enables three-dimension (3D) light control between two turbid layers. A digital optical phase conjugation mirror measured and conjugated the diffused wavefront, which originated from a quasi-point source on the front turbid layer and passed through the back turbid layer. And then, because of memory effect, the phase-conjugated wavefront could be used as a carrier wave to transport a pre-calculated wavefront through the back turbid layer. The pre-calculated wavefront could project a desired 3D light field inside the sample, which, in our experiments, consisted of two 220-grid ground glass plates spaced by a 20 mm distance. The controllable range of light, according to the memory effect, was calculated to be 80 mrad in solid angle and 16 mm on z-axis. Due to the 3D light control ability, our approach may find applications in photodynamic therapy and optogenetics. Besides, our approach can also be combined with ghost imaging or compressed sensing to achieve 3D imaging between turbid layers.

Coronagraphic Wavefront Control for the ATLAST-9.2m Telescope

NASA Technical Reports Server (NTRS)

Lyon, RIchard G.; Oegerle, William R.; Feinberg, Lee D.; Bolcar, Matthew R.; Dean, Bruce H.; Mosier, Gary E.; Postman, Marc

2010-01-01

The Advanced Technology for Large Aperture Space Telescope (ATLAST) concept was assessed as one of the NASA Astrophysics Strategic Mission Concepts (ASMC) studies. Herein we discuss the 9.2-meter diameter segmented aperture version and its wavefront sensing and control (WFSC) with regards to coronagraphic detection and spectroscopic characterization of exoplanets. The WFSC would consist of at least two levels of sensing and control: (i) an outer coarser level of sensing and control to phase and control the segments and secondary mirror in a manner similar to the James Webb Space Telescope but operating at higher temporal bandwidth, and (ii) an inner, coronagraphic instrument based, fine level of sensing and control for both amplitude and wavefront errors operating at higher temporal bandwidths. The outer loop would control rigid-body actuators on the primary and secondary mirrors while the inner loop would control one or more segmented deformable mirror to suppress the starlight within the coronagraphic field-of view. Herein we discuss the visible nulling coronagraph (VNC) and the requirements it levies on wavefront sensing and control and show the results of closed-loop simulations to assess performance and evaluate the trade space of system level stability versus control bandwidth.

Comparison of astigmatic correction after femtosecond lenticule extraction and wavefront-guided LASIK for myopic astigmatism.

PubMed

Ali, Mohamed A; Kobashi, Hidenaga; Kamiya, Kazutaka; Igarashi, Akihito; Miyake, Toshiyuki; Elewa, Mohamed Ehab M; Komatsu, Mari; Shimizu, Kimiya

2014-12-01

To compare postoperative astigmatic correction between femtosecond lenticule extraction (FLEx) and wavefront-guided LASIK in eyes with myopic astigmatism. Fifty-eight eyes of 41 patients undergoing FLEx and 49 eyes of 29 patients undergoing wavefront-guided LASIK to correct myopic astigmatism were examined. Visual acuity, cylindrical refraction, predictability of the astigmatic correction, and astigmatic vector components were compared between groups 6 months after surgery. There was no statistically significant difference in manifest cylindrical refraction (P = .08) or percentage of eyes within ± 0.50 diopter (D) of its refraction (P = .11) between the surgical procedures. The index of success in FLEx was statistically significantly better than that of wavefront-guided LASIK (P = .02), although there was no significant difference between the groups in other indices (eg, surgically induced astigmatism, target-induced astigmatism, astigmatic correction index, angle of error, difference vector, and flattening index). Subgroup analysis showed that FLEx had a better index of success (P = .02) and difference vector (P = .04) than wavefront-guided LASIK in the low cylinder subgroup; the angle of error in FLEx was significantly smaller than that of wavefront-guided LASIK in the moderate cylinder subgroup (P = .03). Both FLEx and wavefront-guided LASIK worked well for the correction of myopic astigmatism by the 6-month follow-up visit. Although FLEx had a better index of success than wavefront-guided LASIK when using vector analysis, it appears equivalent to wavefront-guided LASIK in terms of visual acuity and the correction of astigmatism. Copyright 2014, SLACK Incorporated.

Adaptive optics; Proceedings of the Meeting, Arlington, VA, April 10, 11, 1985

NASA Astrophysics Data System (ADS)

Ludman, J. E.

Papers are presented on the directed energy program for ballistic missile defense, a self-referencing wavefront interferometer for laser sources, the effects of mirror grating distortions on diffraction spots at wavefront sensors, and the optical design of an all-reflecting, high-resolution camera for active-optics on ground-based telescopes. Also considered are transverse coherence length observations, time dependent statistics of upper atmosphere optical turbulence, high altitude acoustic soundings, and the Cramer-Rao lower bound on wavefront sensor error. Other topics include wavefront reconstruction from noisy slope or difference data using the discrete Fourier transform, acoustooptic adaptive signal processing, the recording of phase deformations on a PLZT wafer for holographic and spatial light modulator applications, and an optical phase reconstructor using a multiplier-accumulator approach. Papers are also presented on an integrated optics wavefront measurement sensor, a new optical preprocessor for automatic vision systems, a model for predicting infrared atmospheric emission fluctuations, and optical logic gates and flip-flops based on polarization-bistable semiconductor lasers.

Analysis of target wavefront error for secondary mirror of a spaceborne telescope

NASA Astrophysics Data System (ADS)

Chang, Shenq-Tsong; Lin, Wei-Cheng; Kuo, Ching-Hsiang; Chan, Chia-Yen; Lin, Yu-Chuan; Huang, Ting-Ming

2014-09-01

During the fabrication of an aspherical mirror, the inspection of the residual wavefront error is critical. In the program of a spaceborne telescope development, primary mirror is made of ZERODUR with clear aperture of 450 mm. The mass is 10 kg after lightweighting. Deformation of mirror due to gravity is expected; hence uniform supporting measured by load cells has been applied to reduce the gravity effect. Inspection has been taken to determine the residual wavefront error at the configuration of mirror face upwards. Correction polishing has been performed according to the measurement. However, after comparing with the data measured by bench test while the primary mirror is at a configuration of mirror face horizontal, deviations have been found for the two measurements. Optical system that is not able to meet the requirement is predicted according to the measured wavefront error by bench test. A target wavefront error of secondary mirror is therefore analyzed to correct that of primary mirror. Optical performance accordingly is presented.

Dynamic testbed demonstration of WFIRST coronagraph low order wavefront sensing and control (LOWFS/C)

NASA Astrophysics Data System (ADS)

Shi, Fang; Cady, Eric; Seo, Byoung-Joon; An, Xin; Balasubramanian, Kunjithapatham; Kern, Brian; Lam, Raymond; Marx, David; Moody, Dwight; Mejia Prada, Camilo; Patterson, Keith; Poberezhskiy, Ilya; Shields, Joel; Sidick, Erkin; Tang, Hong; Trauger, John; Truong, Tuan; White, Victor; Wilson, Daniel; Zhou, Hanying

2017-09-01

To maintain the required performance of WFIRST Coronagraph in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C uses a Zernike wavefront sensor (ZWFS) with the phase shifting disk combined with the starlight rejecting occulting mask. For wavefront error corrections, WFIRST LOWFS/C uses a fast steering mirror (FSM) for line-of-sight (LoS) correction, a focusing mirror for focus drift correction, and one of the two deformable mirrors (DM) for other low order wavefront error (WFE) correction. As a part of technology development and demonstration for WFIRST Coronagraph, a dedicated Occulting Mask Coronagraph (OMC) testbed has been built and commissioned. With its configuration similar to the WFIRST flight coronagraph instrument the OMC testbed consists of two coronagraph modes, Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC), a low order wavefront sensor (LOWFS), and an optical telescope assembly (OTA) simulator which can generate realistic LoS drift and jitter as well as low order wavefront error that would be induced by the WFIRST telescope's vibration and thermal changes. In this paper, we will introduce the concept of WFIRST LOWFS/C, describe the OMC testbed, and present the testbed results of LOWFS sensor performance. We will also present our recent results from the dynamic coronagraph tests in which we have demonstrated of using LOWFS/C to maintain the coronagraph contrast with the presence of WFIRST-like line-of-sight and low order wavefront disturbances.

Wavefront correction and high-resolution in vivo OCT imaging with an objective integrated multi-actuator adaptive lens

PubMed Central

Bonora, Stefano; Jian, Yifan; Zhang, Pengfei; Zam, Azhar; Pugh, Edward N.; Zawadzki, Robert J.; Sarunic, Marinko V.

2015-01-01

Adaptive optics is rapidly transforming microscopy and high-resolution ophthalmic imaging. The adaptive elements commonly used to control optical wavefronts are liquid crystal spatial light modulators and deformable mirrors. We introduce a novel Multi-actuator Adaptive Lens that can correct aberrations to high order, and which has the potential to increase the spread of adaptive optics to many new applications by simplifying its integration with existing systems. Our method combines an adaptive lens with an imaged-based optimization control that allows the correction of images to the diffraction limit, and provides a reduction of hardware complexity with respect to existing state-of-the-art adaptive optics systems. The Multi-actuator Adaptive Lens design that we present can correct wavefront aberrations up to the 4th order of the Zernike polynomial characterization. The performance of the Multi-actuator Adaptive Lens is demonstrated in a wide field microscope, using a Shack-Hartmann wavefront sensor for closed loop control. The Multi-actuator Adaptive Lens and image-based wavefront-sensorless control were also integrated into the objective of a Fourier Domain Optical Coherence Tomography system for in vivo imaging of mouse retinal structures. The experimental results demonstrate that the insertion of the Multi-actuator Objective Lens can generate arbitrary wavefronts to correct aberrations down to the diffraction limit, and can be easily integrated into optical systems to improve the quality of aberrated images. PMID:26368169

Linear-constraint wavefront control for exoplanet coronagraphic imaging systems

NASA Astrophysics Data System (ADS)

Sun, He; Eldorado Riggs, A. J.; Kasdin, N. Jeremy; Vanderbei, Robert J.; Groff, Tyler Dean

2017-01-01

A coronagraph is a leading technology for achieving high-contrast imaging of exoplanets in a space telescope. It uses a system of several masks to modify the diffraction and achieve extremely high contrast in the image plane around target stars. However, coronagraphic imaging systems are very sensitive to optical aberrations, so wavefront correction using deformable mirrors (DMs) is necessary to avoid contrast degradation in the image plane. Electric field conjugation (EFC) and Stroke minimization (SM) are two primary high-contrast wavefront controllers explored in the past decade. EFC minimizes the average contrast in the search areas while regularizing the strength of the control inputs. Stroke minimization calculates the minimum DM commands under the constraint that a target average contrast is achieved. Recently in the High Contrast Imaging Lab at Princeton University (HCIL), a new linear-constraint wavefront controller based on stroke minimization was developed and demonstrated using numerical simulation. Instead of only constraining the average contrast over the entire search area, the new controller constrains the electric field of each single pixel using linear programming, which could led to significant increases in speed of the wavefront correction and also create more uniform dark holes. As a follow-up of this work, another linear-constraint controller modified from EFC is demonstrated theoretically and numerically and the lab verification of the linear-constraint controllers is reported. Based on the simulation and lab results, the pros and cons of linear-constraint controllers are carefully compared with EFC and stroke minimization.

Wavefront-Error Performance Characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Science Instruments

NASA Technical Reports Server (NTRS)

Aronstein, David L.; Smith, J. Scott; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

2016-01-01

The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES). In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing (also known as phase retrieval), and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) plate scale measurements made using a Pseudo-Nonredundant Mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated andor rotated across the exit pupil of the system.Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish the uncertainties of the wavefront error maps.

Wavefront-Error Performance Characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Science Instruments

NASA Technical Reports Server (NTRS)

Aronstein, David L.; Smith, J. Scott; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

2016-01-01

The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) F-number and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated and/or rotated across the exit pupil of the system. Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish the uncertainties of the wavefront-error maps.

Characterization of contour shapes achievable with a MEMS deformable mirror

NASA Astrophysics Data System (ADS)

Zhou, Yaopeng; Bifano, Thomas

2006-01-01

An important consideration in the design of an adaptive optics controller is the range of physical shapes required by the DM to compensate the existing aberrations. Conversely, if the range of surface shapes achievable with a DM is known, its suitability for a particular AO application can be determined. In this paper, we characterize one MEMS DM that was recently developed for vision science applications. The device has 140 actuators supporting a continuous face sheet deformable mirror having 4mm square aperture. The total range of actuation is about 4μm, achieved using electrostatic actuation in an architecture that has been described previously. We incorporated the MEMS mirror into an adaptive optics (AO) testbed to measure its capacity to transform an initially planar wavefront into a wavefront having one of thirty-six orthogonal shapes corresponding to the first seven orders of Zernike polynomials. The testbed included a superluminescent diode source emitting light with a wavelength 630nm, a MEMS DM, and a Shack Hartmann wavefront sensor (SHWS). The DM was positioned in a plane conjugate to the SHWS lenslets, using a pair of relay lenses. Wavefront slope measurements provided by the SHWS were used in an integral controller to regulate DM shape. The control software used the difference between the the wavefront measured by the SHWS and the desired (reference) wavefront as feedback for the DM. The DM is able to produce all 36 terms with a wavefront height root mean square (RMS) from 1.35μm for the lower order Zernike shapes to 0.2μm for the 7th order.

Nonlinear Wavefront Control with All-Dielectric Metasurfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Lei; Kruk, Sergey; Koshelev, Kirill

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves. Here, we suggest a novel and rather general approach for engineering the wavefront ofmore » parametric waves of arbitrary complexity generated by a nonlinear metasurface. We design all-dielectric nonlinear metasurfaces, achieve a highly efficient wavefront control of a third-harmonic field, and demonstrate the generation of nonlinear beams at a designed angle and the generation of nonlinear focusing vortex beams. Lastly, our nonlinear metasurfaces produce phase gradients over a full 0–2π phase range with a 92% diffraction efficiency.« less

Nonlinear Wavefront Control with All-Dielectric Metasurfaces.

PubMed

Wang, Lei; Kruk, Sergey; Koshelev, Kirill; Kravchenko, Ivan; Luther-Davies, Barry; Kivshar, Yuri

2018-06-13

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves. Here, we suggest a novel and rather general approach for engineering the wavefront of parametric waves of arbitrary complexity generated by a nonlinear metasurface. We design all-dielectric nonlinear metasurfaces, achieve a highly efficient wavefront control of a third-harmonic field, and demonstrate the generation of nonlinear beams at a designed angle and the generation of nonlinear focusing vortex beams. Our nonlinear metasurfaces produce phase gradients over a full 0-2π phase range with a 92% diffraction efficiency.

Nonlinear Wavefront Control with All-Dielectric Metasurfaces

DOE PAGES

Wang, Lei; Kruk, Sergey; Koshelev, Kirill; ...

2018-05-11

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves. Here, we suggest a novel and rather general approach for engineering the wavefront ofmore » parametric waves of arbitrary complexity generated by a nonlinear metasurface. We design all-dielectric nonlinear metasurfaces, achieve a highly efficient wavefront control of a third-harmonic field, and demonstrate the generation of nonlinear beams at a designed angle and the generation of nonlinear focusing vortex beams. Lastly, our nonlinear metasurfaces produce phase gradients over a full 0–2π phase range with a 92% diffraction efficiency.« less

Improving the performance of a pyramid wavefront sensor with modal sensitivity compensation.

PubMed

Korkiakoski, Visa; Vérinaud, Christophe; Le Louarn, Miska

2008-01-01

We describe a solution to increase the performance of a pyramid wavefront sensor (P-WFS) under bad seeing conditions. We show that most of the issues involve a reduced sensitivity that depends on the magnitude of the high frequency atmospheric distortions. We demonstrate in end-to-end closed loop adaptive optics simulations that with a modal sensitivity compensation method a high-order system with a nonmodulated P-WFS is robust in conditions with the Fried parameter r 0 at 0.5 microm in the range of 0.05-0.10 m. We also show that the method makes it possible to use a modal predictive control system to reach a total performance improvement of 0.06-0.45 in Strehl ratio at 1.6 microm. Especially at r 0=0.05 m the gain is dramatic.

Wavefront control of high-power laser beams in the National Ignition Facility (NIF)

NASA Astrophysics Data System (ADS)

Zacharias, Richard A.; Bliss, Erlan S.; Winters, Scott; Sacks, Richard A.; Feldman, Mark; Grey, Andrew; Koch, Jeffrey A.; Stolz, Christopher J.; Toeppen, John S.; Van Atta, Lewis; Woods, Bruce W.

2000-04-01

The use of lasers as the driver for inertial confinement fusion and weapons physics experiments is based on their ability to produce high-energy short pulses in a beam with low divergence. Indeed, the focusability of high quality laser beams far exceeds alternate technologies and is a major factor in the rationale for building high power lasers for such applications. The National Ignition Facility (NIF) is a large, 192-beam, high-power laser facility under construction at the Lawrence Livermore National Laboratory for fusion and weapons physics experiments. Its uncorrected minimum focal spot size is limited by laser system aberrations. The NIF includes a Wavefront Control System to correct these aberrations to yield a focal spot small enough for its applications. Sources of aberrations to be corrected include prompt pump-induced distortions in the laser amplifiers, previous-shot thermal distortions, beam off-axis effects, and gravity, mounting, and coating-induced optic distortions. Aberrations from gas density variations and optic-manufacturing figure errors are also partially corrected. This paper provides an overview of the NIF Wavefront Control System and describes the target spot size performance improvement it affords. It describes provisions made to accommodate the NIF's high fluence (laser beam and flashlamp), large wavefront correction range, wavefront temporal bandwidth, temperature and humidity variations, cleanliness requirements, and exception handling requirements (e.g. wavefront out-of-limits conditions).

Wavefront optimized nonlinear microscopy of ex vivo human retinas

NASA Astrophysics Data System (ADS)

Gualda, Emilio J.; Bueno, Juan M.; Artal, Pablo

2010-03-01

A multiphoton microscope incorporating a Hartmann-Shack (HS) wavefront sensor to control the ultrafast laser beam's wavefront aberrations has been developed. This instrument allowed us to investigate the impact of the laser beam aberrations on two-photon autofluorescence imaging of human retinal tissues. We demonstrated that nonlinear microscopy images are improved when laser beam aberrations are minimized by realigning the laser system cavity while wavefront controlling. Nonlinear signals from several human retinal anatomical features have been detected for the first time, without the need of fixation or staining procedures. Beyond the improved image quality, this approach reduces the required excitation power levels, minimizing the side effects of phototoxicity within the imaged sample. In particular, this may be important to study the physiology and function of the healthy and diseased retina.

Closed Loop, DM Diversity-based, Wavefront Correction Algorithm for High Contrast Imaging Systems

NASA Technical Reports Server (NTRS)

Give'on, Amir; Belikov, Ruslan; Shaklan, Stuart; Kasdin, Jeremy

2007-01-01

High contrast imaging from space relies on coronagraphs to limit diffraction and a wavefront control systems to compensate for imperfections in both the telescope optics and the coronagraph. The extreme contrast required (up to 10(exp -10) for terrestrial planets) puts severe requirements on the wavefront control system, as the achievable contrast is limited by the quality of the wavefront. This paper presents a general closed loop correction algorithm for high contrast imaging coronagraphs by minimizing the energy in a predefined region in the image where terrestrial planets could be found. The estimation part of the algorithm reconstructs the complex field in the image plane using phase diversity caused by the deformable mirror. This method has been shown to achieve faster and better correction than classical speckle nulling.

Real-Time Wavefront Control for the PALM-3000 High Order Adaptive Optics System

NASA Technical Reports Server (NTRS)

Truong, Tuan N.; Bouchez, Antonin H.; Dekany, Richard G.; Guiwits, Stephen R.; Roberts, Jennifer E.; Troy, Mitchell

2008-01-01

We present a cost-effective scalable real-time wavefront control architecture based on off-the-shelf graphics processing units hosted in an ultra-low latency, high-bandwidth interconnect PC cluster environment composed of modules written in the component-oriented language of nesC. The architecture enables full-matrix reconstruction of the wavefront at up to 2 KHz with latency under 250 us for the PALM-3000 adaptive optics systems, a state-of-the-art upgrade on the 5.1 meter Hale Telescope that consists of a 64 x 64 subaperture Shack-Hartmann wavefront sensor and a 3368 active actuator high order deformable mirror in series with a 241 active actuator tweeter DM. The architecture can easily scale up to support much larger AO systems at higher rates and lower latency.

LQG control of a deformable mirror adaptive optics system with time-delayed measurements

NASA Astrophysics Data System (ADS)

Anderson, David J.

1991-12-01

This thesis proposes a linear quadratic Gaussian (LQG) control law for a ground-based deformable mirror adaptive optics system. The incoming image wavefront is distorted, primarily in phase, due to the turbulent effects of the earth's atmosphere. The adaptive optics system attempts to compensate for the distortion with a deformable mirror. A Hartman wavefront sensor measures the degree of distortion in the image wavefront. The measurements are input to a Kalman filter which estimates the system states. The state estimates are processed by a linear quadratic regulator which generates the appropriate control voltages to apply to the deformable mirror actuators. The dynamics model for the atmospheric phase distortion consists of 14 Zernike coefficient states; each modeled as a first-order linear time-invariant shaping filter driven by zero-mean white Gaussian noise. The dynamics of the deformable mirror are also model as 14 Zernike coefficients with first-order deterministic dynamics. A significant reduction in total wavefront phase distortion is achieved in the presence of time-delayed measurements. Wavefront sensor sampling rate is the major factor limiting system performance. The Multimode Simulation for Optimal Filter Evaluation (MSOFE) software is the performance evaluation tool of choice for this research.

Phase discrepancy induced from least squares wavefront reconstruction of wrapped phase measurements with high noise or large localized wavefront gradients

NASA Astrophysics Data System (ADS)

Steinbock, Michael J.; Hyde, Milo W.

2012-10-01

Adaptive optics is used in applications such as laser communication, remote sensing, and laser weapon systems to estimate and correct for atmospheric distortions of propagated light in real-time. Within an adaptive optics system, a reconstruction process interprets the raw wavefront sensor measurements and calculates an estimate for the unwrapped phase function to be sent through a control law and applied to a wavefront correction device. This research is focused on adaptive optics using a self-referencing interferometer wavefront sensor, which directly measures the wrapped wavefront phase. Therefore, its measurements must be reconstructed for use on a continuous facesheet deformable mirror. In testing and evaluating a novel class of branch-point- tolerant wavefront reconstructors based on the post-processing congruence operation technique, an increase in Strehl ratio compared to a traditional least squares reconstructor was noted even in non-scintillated fields. To investigate this further, this paper uses wave-optics simulations to eliminate many of the variables from a hardware adaptive optics system, so as to focus on the reconstruction techniques alone. The simulation results along with a discussion of the physical reasoning for this phenomenon are provided. For any applications using a self-referencing interferometer wavefront sensor with low signal levels or high localized wavefront gradients, understanding this phenomena is critical when applying a traditional least squares wavefront reconstructor.

Bimorph deformable mirror: an appropriate wavefront corrector for retinal imaging?

NASA Astrophysics Data System (ADS)

Laut, Sophie; Jones, Steve; Park, Hyunkyu; Horsley, David A.; Olivier, Scot; Werner, John S.

2005-11-01

The purpose of this study was to evaluate the performance of a bimorph deformable mirror from AOptix, inserted into an adaptive optics system designed for in-vivo retinal imaging at high resolution. We wanted to determine its suitability as a wavefront corrector for vision science and ophthalmological instrumentation. We presented results obtained in a closed-loop system, and compared them with previous open-loop performance measurements. Our goal was to obtain precise wavefront reconstruction with rapid convergence of the control algorithm. The quality of the reconstruction was expressed in terms of root-mean-squared wavefront residual error (RMS), and number of frames required to perform compensation. Our instrument used a Hartmann-Shack sensor for the wavefront measurements. We also determined the precision and ability of the deformable mirror to compensate the most common types of aberrations present in the human eye (defocus, cylinder, astigmatism and coma), and the quality of its correction, in terms of maximum amplitude of the corrected wavefront. In addition to wavefront correction, we had also used the closed-loop system to generate an arbitrary aberration pattern by entering the desired Hartmann-Shack centroid locations as input to the AO controller. These centroid locations were computed in Matlab for a user-defined aberration pattern, allowing us to test the ability of the DM to generate and compensate for various aberrations. We conclude that this device, in combination with another DM based on Micro-Electro Mechanical Systems (MEMS) technology, may provide better compensation of the higher-order ocular wavefront aberrations of the human eye

Development of Partially-Coherent Wavefront Propagation Simulation Methods for 3rd and 4th Generation Synchrotron Radiation Sources.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chubar O.; Berman, L; Chu, Y.S.

2012-04-04

Partially-coherent wavefront propagation calculations have proven to be feasible and very beneficial in the design of beamlines for 3rd and 4th generation Synchrotron Radiation (SR) sources. These types of calculations use the framework of classical electrodynamics for the description, on the same accuracy level, of the emission by relativistic electrons moving in magnetic fields of accelerators, and the propagation of the emitted radiation wavefronts through beamline optical elements. This enables accurate prediction of performance characteristics for beamlines exploiting high SR brightness and/or high spectral flux. Detailed analysis of radiation degree of coherence, offered by the partially-coherent wavefront propagation method, ismore » of paramount importance for modern storage-ring based SR sources, which, thanks to extremely small sub-nanometer-level electron beam emittances, produce substantial portions of coherent flux in X-ray spectral range. We describe the general approach to partially-coherent SR wavefront propagation simulations and present examples of such simulations performed using 'Synchrotron Radiation Workshop' (SRW) code for the parameters of hard X-ray undulator based beamlines at the National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory. These examples illustrate general characteristics of partially-coherent undulator radiation beams in low-emittance SR sources, and demonstrate advantages of applying high-accuracy physical-optics simulations to the optimization and performance prediction of X-ray optical beamlines in these new sources.« less

The Gemini Planet Imager Calibration Wavefront Sensor Instrument

NASA Technical Reports Server (NTRS)

Wallace, J. Kent; Burruss, Rick S.; Bartos, Randall D.; Trinh, Thang Q.; Pueyo, Laurent A.; Fregoso, Santos F.; Angione, John R.; Shelton, J. Chris

2010-01-01

The Gemini Planet Imager is an extreme adaptive optics system that will employ an apodized-pupil coronagraph to make direct detections of faint companions of nearby stars to a contrast level of the 10(exp -7) within a few lambda/D of the parent star. Such high contrasts from the ground require exquisite wavefront sensing and control both for the AO system as well as for the coronagraph. Un-sensed non-common path phase and amplitude errors after the wavefront sensor dichroic but before the coronagraph would lead to speckles which would ultimately limit the contrast. The calibration wavefront system for GPI will measure the complex wavefront at the system pupil before the apodizer and provide slow phase corrections to the AO system to mitigate errors that would cause a loss in contrast. The calibration wavefront sensor instrument for GPI has been built. We will describe the instrument and its performance.

End-to-end Coronagraphic Modeling Including a Low-order Wavefront Sensor

NASA Technical Reports Server (NTRS)

Krist, John E.; Trauger, John T.; Unwin, Stephen C.; Traub, Wesley A.

2012-01-01

To evaluate space-based coronagraphic techniques, end-to-end modeling is necessary to simulate realistic fields containing speckles caused by wavefront errors. Real systems will suffer from pointing errors and thermal and motioninduced mechanical stresses that introduce time-variable wavefront aberrations that can reduce the field contrast. A loworder wavefront sensor (LOWFS) is needed to measure these changes at a sufficiently high rate to maintain the contrast level during observations. We implement here a LOWFS and corresponding low-order wavefront control subsystem (LOWFCS) in end-to-end models of a space-based coronagraph. Our goal is to be able to accurately duplicate the effect of the LOWFS+LOWFCS without explicitly evaluating the end-to-end model at numerous time steps.

High-resolution wavefront control of high-power laser systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brase, J; Brown, C; Carrano, C

1999-07-08

Nearly every new large-scale laser system application at LLNL has requirements for beam control which exceed the current level of available technology. For applications such as inertial confinement fusion, laser isotope separation, laser machining, and laser the ability to transport significant power to a target while maintaining good beam quality is critical. There are many ways that laser wavefront quality can be degraded. Thermal effects due to the interaction of high-power laser or pump light with the internal optical components or with the ambient gas are common causes of wavefront degradation. For many years, adaptive optics based on thing deformablemore » glass mirrors with piezoelectric or electrostrictive actuators have be used to remove the low-order wavefront errors from high-power laser systems. These adaptive optics systems have successfully improved laser beam quality, but have also generally revealed additional high-spatial-frequency errors, both because the low-order errors have been reduced and because deformable mirrors have often introduced some high-spatial-frequency components due to manufacturing errors. Many current and emerging laser applications fall into the high-resolution category where there is an increased need for the correction of high spatial frequency aberrations which requires correctors with thousands of degrees of freedom. The largest Deformable Mirrors currently available have less than one thousand degrees of freedom at a cost of approximately $1M. A deformable mirror capable of meeting these high spatial resolution requirements would be cost prohibitive. Therefore a new approach using a different wavefront control technology is needed. One new wavefront control approach is the use of liquid-crystal (LC) spatial light modulator (SLM) technology for the controlling the phase of linearly polarized light. Current LC SLM technology provides high-spatial-resolution wavefront control, with hundreds of thousands of degrees of freedom, more than two orders of magnitude greater than the best Deformable Mirrors currently made. Even with the increased spatial resolution, the cost of these devices is nearly two orders of magnitude less than the cost of the largest deformable mirror.« less

Pattern placement errors: application of in-situ interferometer-determined Zernike coefficients in determining printed image deviations

NASA Astrophysics Data System (ADS)

Roberts, William R.; Gould, Christopher J.; Smith, Adlai H.; Rebitz, Ken

2000-08-01

Several ideas have recently been presented which attempt to measure and predict lens aberrations for new low k1 imaging systems. Abbreviated sets of Zernike coefficients have been produced and used to predict Across Chip Linewidth Variation. Empirical use of the wavefront aberrations can now be used in commercially available lithography simulators to predict pattern distortion and placement errors. Measurement and Determination of Zernike coefficients has been a significant effort of many. However the use of this data has generally been limited to matching lenses or picking best fit lense pairs. We will use wavefront aberration data collected using the Litel InspecStep in-situ Interferometer as input data for Prolith/3D to model and predict pattern placement errors and intrafield overlay variation. Experiment data will be collected and compared to the simulated predictions.

Discovery Channel Telescope active optics system early integration and test

NASA Astrophysics Data System (ADS)

Venetiou, Alexander J.; Bida, Thomas A.

2012-09-01

The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chrétien (RC) with an unvignetted 0.5° Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system. In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly (PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop feed-forward coefficients determination. In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.

Predictor-corrector framework for the sequential assembly of optical systems based on wavefront sensing.

PubMed

Schindlbeck, Christopher; Pape, Christian; Reithmeier, Eduard

2018-04-16

Alignment of optical components is crucial for the assembly of optical systems to ensure their full functionality. In this paper we present a novel predictor-corrector framework for the sequential assembly of serial optical systems. Therein, we use a hybrid optical simulation model that comprises virtual and identified component positions. The hybrid model is constantly adapted throughout the assembly process with the help of nonlinear identification techniques and wavefront measurements. This enables prediction of the future wavefront at the detector plane and therefore allows for taking corrective measures accordingly during the assembly process if a user-defined tolerance on the wavefront error is violated. We present a novel notation for the so-called hybrid model and outline the work flow of the presented predictor-corrector framework. A beam expander is assembled as demonstrator for experimental verification of the framework. The optical setup consists of a laser, two bi-convex spherical lenses each mounted to a five degree-of-freedom stage to misalign and correct components, and a Shack-Hartmann sensor for wavefront measurements.

Method for removing tilt control in adaptive optics systems

DOEpatents

Salmon, Joseph Thaddeus

1998-01-01

A new adaptive optics system and method of operation, whereby the method removes tilt control, and includes the steps of using a steering mirror to steer a wavefront in the desired direction, for aiming an impinging aberrated light beam in the direction of a deformable mirror. The deformable mirror has its surface deformed selectively by means of a plurality of actuators, and compensates, at least partially, for existing aberrations in the light beam. The light beam is split into an output beam and a sample beam, and the sample beam is sampled using a wavefront sensor. The sampled signals are converted into corresponding electrical signals for driving a controller, which, in turn, drives the deformable mirror in a feedback loop in response to the sampled signals, for compensating for aberrations in the wavefront. To this purpose, a displacement error (gradient) of the wavefront is measured, and adjusted by a modified gain matrix, which satisfies the following equation: G'=(I-X(X.sup.T X).sup.-1 X.sup.T)G(I-A)

Wavefront Compensation Segmented Mirror Sensing and Control

NASA Technical Reports Server (NTRS)

Redding, David C.; Lou, John Z.; Kissil, Andrew; Bradford, Charles M.; Woody, David; Padin, Stephen

2012-01-01

The primary mirror of very large submillimeter-wave telescopes will necessarily be segmented into many separate mirror panels. These panels must be continuously co-phased to keep the telescope wavefront error less than a small fraction of a wavelength, to ten microns RMS (root mean square) or less. This performance must be maintained continuously across the full aperture of the telescope, in all pointing conditions, and in a variable thermal environment. A wavefront compensation segmented mirror sensing and control system, consisting of optical edge sensors, Wavefront Compensation Estimator/Controller Soft ware, and segment position actuators is proposed. Optical edge sensors are placed two per each segment-to-segment edge to continuously measure changes in segment state. Segment position actuators (three per segment) are used to move the panels. A computer control system uses the edge sensor measurements to estimate the state of all of the segments and to predict the wavefront error; segment actuator commands are computed that minimize the wavefront error. Translational or rotational motions of one segment relative to the other cause lateral displacement of the light beam, which is measured by the imaging sensor. For high accuracy, the collimator uses a shaped mask, such as one or more slits, so that the light beam forms a pattern on the sensor that permits sensing accuracy of better than 0.1 micron in two axes: in the z or local surface normal direction, and in the y direction parallel to the mirror surface and perpendicular to the beam direction. Using a co-aligned pair of sensors, with the location of the detector and collimated light source interchanged, four degrees of freedom can be sensed: transverse x and y displacements, as well as two bending angles (pitch and yaw). In this approach, each optical edge sensor head has a collimator and an imager, placing one sensor head on each side of a segment gap, with two parallel light beams crossing the gap. Two sets of optical edge sensors are used per segment-to-segment edge, separated by a finite distance along the segment edge, for four optical heads, each with an imager and a collimator. By orienting the beam direction of one edge sensor pair to be +45 away from the segment edge direction, and the other sensor pair to be oriented -45 away from the segment edge direction, all six degrees of freedom of relative motion between the segments can be measured with some redundancy. The software resides in a computer that receives each of the optical edge sensor signals, as well as telescope pointing commands. It feeds back the edge sensor signals to keep the primary mirror figure within specification. It uses a feed-forward control to compensate for global effects such as decollimation of the primary and secondary mirrors due to gravity sag as the telescope pointing changes to track science objects. Three segment position actuators will be provided per segment to enable controlled motions in the piston, tip, and tilt degrees of freedom. These actuators are driven by the software, providing the optical changes needed to keep the telescope phased.

Techniques for High Contrast Imaging in Multi-Star Systems II: Multi-Star Wavefront Control

NASA Technical Reports Server (NTRS)

Sirbu, D.; Thomas, S.; Belikov, R.

2017-01-01

Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments because of the diffraction and aberration leakage introduced by the additional stars, and as a result are not planned to be on direct imaging target lists. Multi-star wavefront control (MSWC) is a technique that uses a coronagraphic instrument's deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. Our previous paper introduced the Super-Nyquist Wavefront Control (SNWC) technique that uses a diffraction grating to enable the DM to generate high-contrast regions beyond the nominal controllable region. These two techniques can be combined to generate high-contrast regions for multi-star systems at any angular separations. As a case study, a high-contrast wavefront control (WC) simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged reaching 8 times 10(exp -9) mean contrast in 10 percent broadband light in one-sided dark holes from 1.6-5.5 lambda (wavelength) divided by D (distance).

Design and Validation of an Infrared Badal Optometer for Laser Speckle (IBOLS)

PubMed Central

Teel, Danielle F. W.; Copland, R. James; Jacobs, Robert J.; Wells, Thad; Neal, Daniel R.; Thibos, Larry N.

2009-01-01

Purpose To validate the design of an infrared wavefront aberrometer with a Badal optometer employing the principle of laser speckle generated by a spinning disk and infrared light. The instrument was designed for subjective meridional refraction in infrared light by human patients. Methods Validation employed a model eye with known refractive error determined with an objective infrared wavefront aberrometer. The model eye was used to produce a speckle pattern on an artificial retina with controlled amounts of ametropia introduced with auxiliary ophthalmic lenses. A human observer performed the psychophysical task of observing the speckle pattern (with the aid of a video camera sensitive to infrared radiation) formed on the artificial retina. Refraction was performed by adjusting the vergence of incident light with the Badal optometer to nullify the motion of laser speckle. Validation of the method was performed for different levels of spherical ametropia and for various configurations of an astigmatic model eye. Results Subjective measurements of meridional refractive error over the range −4D to + 4D agreed with astigmatic refractive errors predicted by the power of the model eye in the meridian of motion of the spinning disk. Conclusions Use of a Badal optometer to control laser speckle is a valid method for determining subjective refractive error at infrared wavelengths. Such an instrument will be useful for comparing objective measures of refractive error obtained for the human eye with autorefractors and wavefront aberrometers that employ infrared radiation. PMID:18772719

An Update on the Role of Systems Modeling in the Design and Verification of the James Webb Space Telescope

NASA Technical Reports Server (NTRS)

Muheim, Danniella; Menzel, Michael; Mosier, Gary; Irish, Sandra; Maghami, Peiman; Mehalick, Kimberly; Parrish, Keith

2010-01-01

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014. System-level verification of critical performance requirements will rely on integrated observatory models that predict the wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms) through to the wave-front sensor focal plane is met. The assembled models themselves are complex and require the insight of technical experts to assess their ability to meet their objectives. This paper describes the systems engineering and modeling approach used on the JWST through the detailed design phase.

Collaborative effects of wavefront shaping and optical clearing agent in optical coherence tomography

NASA Astrophysics Data System (ADS)

Yu, Hyeonseung; Lee, Peter; Jo, YoungJu; Lee, KyeoReh; Tuchin, Valery V.; Jeong, Yong; Park, YongKeun

2016-12-01

We demonstrate that simultaneous application of optical clearing agents (OCAs) and complex wavefront shaping in optical coherence tomography (OCT) can provide significant enhancement of penetration depth and imaging quality. OCA reduces optical inhomogeneity of a highly scattering sample, and the wavefront shaping of illumination light controls multiple scattering, resulting in an enhancement of the penetration depth and signal-to-noise ratio. A tissue phantom study shows that concurrent applications of OCA and wavefront shaping successfully operate in OCT imaging. The penetration depth enhancement is further demonstrated for ex vivo mouse ears, revealing hidden structures inaccessible with conventional OCT imaging.

MEMS deformable mirror for wavefront correction of large telescopes

NASA Astrophysics Data System (ADS)

Manhart, Sigmund; Vdovin, Gleb; Collings, Neil; Sodnik, Zoran; Nikolov, Susanne; Hupfer, Werner

2017-11-01

A 50 mm diameter membrane mirror was designed and manufactured at TU Delft. It is made from bulk silicon by micromachining - a technology primarily used for micro-electromechanical systems (MEMS). The mirror unit is equipped with 39 actuator electrodes and can be electrostatically deformed to correct wavefront errors in optical imaging systems. Performance tests on the deformable mirror were carried out at Astrium GmbH using a breadboard setup with a wavefront sensor and a closed-loop control system. It was found that the deformable membrane mirror is well suited for correction of low order wavefront errors as they must be expected in lightweighted space telescopes.

Optimizing wavefront-guided corrections for highly aberrated eyes in the presence of registration uncertainty

PubMed Central

Shi, Yue; Queener, Hope M.; Marsack, Jason D.; Ravikumar, Ayeswarya; Bedell, Harold E.; Applegate, Raymond A.

2013-01-01

Dynamic registration uncertainty of a wavefront-guided correction with respect to underlying wavefront error (WFE) inevitably decreases retinal image quality. A partial correction may improve average retinal image quality and visual acuity in the presence of registration uncertainties. The purpose of this paper is to (a) develop an algorithm to optimize wavefront-guided correction that improves visual acuity given registration uncertainty and (b) test the hypothesis that these corrections provide improved visual performance in the presence of these uncertainties as compared to a full-magnitude correction or a correction by Guirao, Cox, and Williams (2002). A stochastic parallel gradient descent (SPGD) algorithm was used to optimize the partial-magnitude correction for three keratoconic eyes based on measured scleral contact lens movement. Given its high correlation with logMAR acuity, the retinal image quality metric log visual Strehl was used as a predictor of visual acuity. Predicted values of visual acuity with the optimized corrections were validated by regressing measured acuity loss against predicted loss. Measured loss was obtained from normal subjects viewing acuity charts that were degraded by the residual aberrations generated by the movement of the full-magnitude correction, the correction by Guirao, and optimized SPGD correction. Partial-magnitude corrections optimized with an SPGD algorithm provide at least one line improvement of average visual acuity over the full magnitude and the correction by Guirao given the registration uncertainty. This study demonstrates that it is possible to improve the average visual acuity by optimizing wavefront-guided correction in the presence of registration uncertainty. PMID:23757512

Advanced Wavefront Sensing and Control Testbed (AWCT)

NASA Technical Reports Server (NTRS)

Shi, Fang; Basinger, Scott A.; Diaz, Rosemary T.; Gappinger, Robert O.; Tang, Hong; Lam, Raymond K.; Sidick, Erkin; Hein, Randall C.; Rud, Mayer; Troy, Mitchell

2010-01-01

The Advanced Wavefront Sensing and Control Testbed (AWCT) is built as a versatile facility for developing and demonstrating, in hardware, the future technologies of wave front sensing and control algorithms for active optical systems. The testbed includes a source projector for a broadband point-source and a suite of extended scene targets, a dispersed fringe sensor, a Shack-Hartmann camera, and an imaging camera capable of phase retrieval wavefront sensing. The testbed also provides two easily accessible conjugated pupil planes which can accommodate the active optical devices such as fast steering mirror, deformable mirror, and segmented mirrors. In this paper, we describe the testbed optical design, testbed configurations and capabilities, as well as the initial results from the testbed hardware integrations and tests.

Terahertz wavefront control by tunable metasurface made of graphene ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yatooshi, Takumi; Ishikawa, Atsushi, E-mail: a-ishikawa@okayama-u.ac.jp; Tsuruta, Kenji

2015-08-03

We propose a tunable metasurface consisting of an array of graphene ribbons on a silver mirror with a SiO{sub 2} gap layer to control reflected wavefront at terahertz frequencies. The graphene ribbons exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO{sub 2} layer, phase shift through the system is largely accumulated, covering the 0-to-2π range for full control of the wavefront. Numerical simulations prove that wide-angle beam steering up to 53° with a high reflection efficiency of 60% is achieved at 5 THzmore » within a switching time shorter than 0.6 ps.« less

Visual Outcomes After LASIK Using Topography-Guided vs Wavefront-Guided Customized Ablation Systems.

PubMed

Toda, Ikuko; Ide, Takeshi; Fukumoto, Teruki; Tsubota, Kazuo

2016-11-01

To evaluate the visual performance of two customized ablation systems (wavefront-guided ablation and topography-guided ablation) in LASIK. In this prospective, randomized clinical study, 68 eyes of 35 patients undergoing LASIK were enrolled. Patients were randomly assigned to wavefront-guided ablation using the iDesign aberrometer and STAR S4 IR Excimer Laser system (Abbott Medical Optics, Inc., Santa Ana, CA) (wavefront-guided group; 32 eyes of 16 patients; age: 29.0 ± 7.3 years) or topography-guided ablation using the OPD-Scan aberrometer and EC-5000 CXII excimer laser system (NIDEK, Tokyo, Japan) (topography-guided group; 36 eyes of 19 patients; age: 36.1 ± 9.6 years). Preoperative manifest refraction was -4.92 ± 1.95 diopters (D) in the wavefront-guided group and -4.44 ± 1.98 D in the topography-guided group. Visual function and subjective symptoms were compared between groups before and 1 and 3 months after LASIK. Of seven subjective symptoms evaluated, four were significantly milder in the wavefront-guided group at 3 months. Contrast sensitivity with glare off at low spatial frequencies (6.3° and 4°) was significantly higher in the wavefront-guided group. Uncorrected and corrected distance visual acuity, manifest refraction, and higher order aberrations measured by OPD-Scan and iDesign were not significantly different between the two groups at 1 and 3 months after LASIK. Both customized ablation systems used in LASIK achieved excellent results in predictability and visual function. The wavefront-guided ablation system may have some advantages in the quality of vision. It may be important to select the appropriate system depending on eye conditions such as the pattern of total and corneal higher order aberrations. [J Refract Surg. 2016;32(11):727-732.]. Copyright 2016, SLACK Incorporated.

Fitting relationship between the beam quality β factor of high-energy laser and the wavefront aberration of laser beam

NASA Astrophysics Data System (ADS)

Ji, Zhong-Ye; Zhang, Xiao-Fang

2018-01-01

The mathematical relation between the beam quality β factor of high-energy laser and the wavefront aberration of laser beam is important in beam quality control theory of the high-energy laser weapon system. In order to obtain this mathematical relation, numerical simulation is used in the research. Firstly, the Zernike representations of typically distorted atmospheric wavefront aberrations caused by the Kolmogoroff turbulence are generated. And then, the corresponding beam quality β factors of the different distorted wavefronts are calculated numerically through fast Fourier transform. Thus, the statistical distribution rule between the beam quality β factors of high-energy laser and the wavefront aberrations of the beam can be established by the calculated results. Finally, curve fitting method is chosen to establish the mathematical fitting relationship of these two parameters. And the result of the curve fitting shows that there is a quadratic curve relation between the beam quality β factor of high-energy laser and the wavefront aberration of laser beam. And in this paper, 3 fitting curves, in which the wavefront aberrations are consisted of Zernike Polynomials of 20, 36, 60 orders individually, are established to express the relationship between the beam quality β factor and atmospheric wavefront aberrations with different spatial frequency.

Non-common path aberration correction in an adaptive optics scanning ophthalmoscope.

PubMed

Sulai, Yusufu N; Dubra, Alfredo

2014-09-01

The correction of non-common path aberrations (NCPAs) between the imaging and wavefront sensing channel in a confocal scanning adaptive optics ophthalmoscope is demonstrated. NCPA correction is achieved by maximizing an image sharpness metric while the confocal detection aperture is temporarily removed, effectively minimizing the monochromatic aberrations in the illumination path of the imaging channel. Comparison of NCPA estimated using zonal and modal orthogonal wavefront corrector bases provided wavefronts that differ by ~λ/20 in root-mean-squared (~λ/30 standard deviation). Sequential insertion of a cylindrical lens in the illumination and light collection paths of the imaging channel was used to compare image resolution after changing the wavefront correction to maximize image sharpness and intensity metrics. Finally, the NCPA correction was incorporated into the closed-loop adaptive optics control by biasing the wavefront sensor signals without reducing its bandwidth.

Subwavelength diffractive acoustics and wavefront manipulation with a reflective acoustic metasurface

NASA Astrophysics Data System (ADS)

Wang, Wenqi; Xie, Yangbo; Popa, Bogdan-Ioan; Cummer, Steven A.

2016-11-01

Acoustic metasurfaces provide useful wavefront shaping capabilities, such as beam steering, acoustic focusing, and asymmetric transmission, in a compact structure. Most acoustic metasurfaces described in the literature are transmissive devices and focus their performance on steering sound beam of the fundamental diffractive order. In addition, the range of incident angles studied is usually below the critical incidence predicted by generalized Snell's law of reflection. In this work, we comprehensively analyze the wave interaction with a generic periodic phase-modulating structure in order to predict the behavior of all diffractive orders, especially for cases beyond critical incidence. Under the guidance of the presented analysis, a broadband reflective metasurface is designed based on an expanded library of labyrinthine acoustic metamaterials. Various local and nonlocal wavefront shaping properties are experimentally demonstrated, and enhanced absorption of higher order diffractive waves is experimentally shown for the first time. The proposed methodology provides an accurate approach for predicting practical diffracted wave behaviors and opens a new perspective for the study of acoustic periodic structures. The designed metasurface extends the functionalities of acoustic metasurfaces and paves the way for the design of thin planar reflective structures for broadband acoustic wave manipulation and extraordinary absorption.

The clock and wavefront model revisited.

PubMed

Murray, Philip J; Maini, Philip K; Baker, Ruth E

2011-08-21

The currently accepted interpretation of the clock and wavefront model of somitogenesis is that a posteriorly moving molecular gradient sequentially slows the rate of clock oscillations, resulting in a spatial readout of temporal oscillations. However, while molecular components of the clocks and wavefronts have now been identified in the pre-somitic mesoderm (PSM), there is not yet conclusive evidence demonstrating that the observed molecular wavefronts act to slow clock oscillations. Here we present an alternative formulation of the clock and wavefront model in which oscillator coupling, already known to play a key role in oscillator synchronisation, plays a fundamentally important role in the slowing of oscillations along the anterior-posterior (AP) axis. Our model has three parameters which can be determined, in any given species, by the measurement of three quantities: the clock period in the posterior PSM, somite length and the length of the PSM. A travelling wavefront, which slows oscillations along the AP axis, is an emergent feature of the model. Using the model we predict: (a) the distance between moving stripes of gene expression; (b) the number of moving stripes of gene expression and (c) the oscillator period profile along the AP axis. Predictions regarding the stripe data are verified using existing zebrafish data. We simulate a range of experimental perturbations and demonstrate how the model can be used to unambiguously define a reference frame along the AP axis. Comparing data from zebrafish, chick, mouse and snake, we demonstrate that: (a) variation in patterning profiles is accounted for by a single nondimensional parameter; the ratio of coupling strengths; and (b) the period profile along the AP axis is conserved across species. Thus the model is consistent with the idea that, although the genes involved in pattern propagation in the PSM vary, there is a conserved patterning mechanism across species. Copyright © 2011 Elsevier Ltd. All rights reserved.

Testing of Lagrange multiplier damped least-squares control algorithm for woofer-tweeter adaptive optics

PubMed Central

Zou, Weiyao; Burns, Stephen A.

2012-01-01

A Lagrange multiplier-based damped least-squares control algorithm for woofer-tweeter (W-T) dual deformable-mirror (DM) adaptive optics (AO) is tested with a breadboard system. We show that the algorithm can complementarily command the two DMs to correct wavefront aberrations within a single optimization process: the woofer DM correcting the high-stroke, low-order aberrations, and the tweeter DM correcting the low-stroke, high-order aberrations. The optimal damping factor for a DM is found to be the median of the eigenvalue spectrum of the influence matrix of that DM. Wavefront control accuracy is maximized with the optimized control parameters. For the breadboard system, the residual wavefront error can be controlled to the precision of 0.03 μm in root mean square. The W-T dual-DM AO has applications in both ophthalmology and astronomy. PMID:22441462

Testing of Lagrange multiplier damped least-squares control algorithm for woofer-tweeter adaptive optics.

PubMed

Zou, Weiyao; Burns, Stephen A

2012-03-20

A Lagrange multiplier-based damped least-squares control algorithm for woofer-tweeter (W-T) dual deformable-mirror (DM) adaptive optics (AO) is tested with a breadboard system. We show that the algorithm can complementarily command the two DMs to correct wavefront aberrations within a single optimization process: the woofer DM correcting the high-stroke, low-order aberrations, and the tweeter DM correcting the low-stroke, high-order aberrations. The optimal damping factor for a DM is found to be the median of the eigenvalue spectrum of the influence matrix of that DM. Wavefront control accuracy is maximized with the optimized control parameters. For the breadboard system, the residual wavefront error can be controlled to the precision of 0.03 μm in root mean square. The W-T dual-DM AO has applications in both ophthalmology and astronomy. © 2012 Optical Society of America

Ocular wavefront aberrations in patients with macular diseases

PubMed Central

Bessho, Kenichiro; Bartsch, Dirk-Uwe G.; Gomez, Laura; Cheng, Lingyun; Koh, Hyoung Jun; Freeman, William R.

2009-01-01

Background There have been reports that by compensating for the ocular aberrations using adaptive optical systems it may be possible to improve the resolution of clinical retinal imaging systems beyond what is now possible. In order to develop such system to observe eyes with retinal disease, understanding of the ocular wavefront aberrations in individuals with retinal disease is required. Methods 82 eyes of 66 patients with macular disease (epiretinal membrane, macular edema, macular hole etc.) and 85 eyes of 51 patients without retinal disease were studied. Using a ray-tracing wavefront device, each eye was scanned at both small and large pupil apertures and Zernike coefficients up to 6th order were acquired. Results In phakic eyes, 3rd order root mean square errors (RMS) in macular disease group were statistically greater than control, an average of 12% for 5mm and 31% for 3mm scan diameters (p<0.021). In pseudophakic eyes, there also was an elevation of 3rd order RMS, on average 57% for 5mm and 51% for 3mm scan diameters (p<0.031). Conclusion Higher order wavefront aberrations in eyes with macular disease were greater than in control eyes without disease. Our study suggests that such aberrations may result from irregular or multiple reflecting retinal surfaces. Modifications in wavefront sensor technology will be needed to accurately determine wavefront aberration and allow correction using adaptive optics in eyes with macular irregularities. PMID:19574950

A comparison of the Maslov integral seismogram and the finite-difference method

NASA Astrophysics Data System (ADS)

Huang, X.; Kendall, J.-M.; Thomson, C. J.; West, G. F.

1998-03-01

The Maslov asymptotic method addresses some of the problems with standard ray theory, such as caustics and shadows. However, it has been applied relatively little, perhaps because its accuracy remains untested. In this study we examine Maslov integral (MI) seismograms by comparing them with finite-difference (FD) seismograms for several cases of interest, such as (1) velocity gradients generating traveltime triplications and shadows, (2) wave-front bending, kinking and folding in a low-velocity waveguide, and (3) wavefield propagation perturbed by a high-velocity slab. The results show that many features of high- and intermediate-frequency waveforms are reliably predicted by Maslov's technique, but also that it is far less reliable and even fails for low frequencies. The terms `high' and `low' are model-dependent, but we mean the range over which it is sensible to discuss signals associated with identifiable wave fronts and local (if complicated) effects that potentially can be unravelled in interpretation. Of the high- and intermediate-frequency wave components, those wave- front anomalies due to wave-front bending, kinking, folding or rapid ray divergence can be accurately given by MI. True diffractions due to secondary wave-front sections are theoretically not included in Maslov theory (as they require true diffracted rays), but in practice they can often be satisfactorily predicted. This occurs roughly within a wavelength of the truncated geometrical wave front, where such diffractions are most important since their amplitudes may still be as large as half that on the geometrical wave front itself. Outside this region MI is inaccurate (although then the diffractions are usually small). Thus waveforms of high and intermediate frequencies are essentially controlled by classical wave-front geometry. Our results also show that the accuracy of MI can be improved by rotating the Maslov integration axis so that the nearest wave-front anomaly is adequately `sampled'. This rotation can be performed after ray tracing and it can serve to avoid pseudo-caustics by using it in conjunction with the phase-partitioning approach. The effort needed in phase partitioning has been reduced by using an interactive graphics technique. It is difficult to formulate a general rule prescribing the limitations of MI accuracy because of model dependency. However, our experiences indicate that two space- and two timescales need to be considered. These are the pulse width in space, the length scale over which the instantaneous wave-front curvature changes, and the timescales of pulse width and significant features in the ray traveltime curve. It seems, from our examples, that when these scales are comparable, the Maslov method gives very acceptable results.

Method for removing tilt control in adaptive optics systems

DOEpatents

Salmon, J.T.

1998-04-28

A new adaptive optics system and method of operation are disclosed, whereby the method removes tilt control, and includes the steps of using a steering mirror to steer a wavefront in the desired direction, for aiming an impinging aberrated light beam in the direction of a deformable mirror. The deformable mirror has its surface deformed selectively by means of a plurality of actuators, and compensates, at least partially, for existing aberrations in the light beam. The light beam is split into an output beam and a sample beam, and the sample beam is sampled using a wavefront sensor. The sampled signals are converted into corresponding electrical signals for driving a controller, which, in turn, drives the deformable mirror in a feedback loop in response to the sampled signals, for compensating for aberrations in the wavefront. To this purpose, a displacement error (gradient) of the wavefront is measured, and adjusted by a modified gain matrix, which satisfies the following equation: G{prime} = (I{minus}X(X{sup T} X){sup {minus}1}X{sup T})G(I{minus}A). 3 figs.

High-contrast imager for complex aperture telescopes (HiCAT): 3. first lab results with wavefront control

NASA Astrophysics Data System (ADS)

N'Diaye, Mamadou; Mazoyer, Johan; Choquet, Élodie; Pueyo, Laurent; Perrin, Marshall D.; Egron, Sylvain; Leboulleux, Lucie; Levecq, Olivier; Carlotti, Alexis; Long, Chris A.; Lajoie, Rachel; Soummer, Rémi

2015-09-01

HiCAT is a high-contrast imaging testbed designed to provide complete solutions in wavefront sensing, control and starlight suppression with complex aperture telescopes. The pupil geometry of such observatories includes primary mirror segmentation, central obstruction, and spider vanes, which make the direct imaging of habitable worlds very challenging. The testbed alignment was completed in the summer of 2014, exceeding specifications with a total wavefront error of 12nm rms over a 18mm pupil. The installation of two deformable mirrors for wavefront control is to be completed in the winter of 2015. In this communication, we report on the first testbed results using a classical Lyot coronagraph. We also present the coronagraph design for HiCAT geometry, based on our recent development of Apodized Pupil Lyot Coronagraph (APLC) with shaped-pupil type optimizations. These new APLC-type solutions using two-dimensional shaped-pupil apodizer render the system quasi-insensitive to jitter and low-order aberrations, while improving the performance in terms of inner working angle, bandpass and contrast over a classical APLC.

Thirty Meter Telescope narrow-field infrared adaptive optics system real-time controller prototyping results

NASA Astrophysics Data System (ADS)

Smith, Malcolm; Kerley, Dan; Chapin, Edward L.; Dunn, Jennifer; Herriot, Glen; Véran, Jean-Pierre; Boyer, Corinne; Ellerbroek, Brent; Gilles, Luc; Wang, Lianqi

2016-07-01

Prototyping and benchmarking was performed for the Real-Time Controller (RTC) of the Narrow Field InfraRed Adaptive Optics System (NFIRAOS). To perform wavefront correction, NFIRAOS utilizes two deformable mirrors (DM) and one tip/tilt stage (TTS). The RTC receives wavefront information from six Laser Guide Star (LGS) Shack- Hartmann WaveFront Sensors (WFS), one high-order Natural Guide Star Pyramid WaveFront Sensor (PWFS) and multiple low-order instrument detectors. The RTC uses this information to determine the commands to send to the wavefront correctors. NFIRAOS is the first light AO system for the Thirty Meter Telescope (TMT). The prototyping was performed using dual-socket high performance Linux servers with the real-time (PREEMPT_RT) patch and demonstrated the viability of a commercial off-the-shelf (COTS) hardware approach to large scale AO reconstruction. In particular, a large custom matrix vector multiplication (MVM) was benchmarked which met the required latency requirements. In addition all major inter-machine communication was verified to be adequate using 10Gb and 40Gb Ethernet. The results of this prototyping has enabled a CPU-based NFIRAOS RTC design to proceed with confidence and that COTS hardware can be used to meet the demanding performance requirements.

Wavefront Correction for Large, Flexible Antenna Reflector

NASA Technical Reports Server (NTRS)

Imbriale, William A.; Jammejad, Vahraz; Rajagopalan, Harish; Xu, Shenheng

2010-01-01

A wavefront-correction system has been proposed as part of an outer-space radio communication system that would include a large, somewhat flexible main reflector antenna, a smaller subreflector antenna, and a small array feed at the focal plane of these two reflector antennas. Part of the wavefront-correction system would reside in the subreflector, which would be a planar patch-element reflectarray antenna in which the phase shifts of the patch antenna elements would be controlled via microelectromechanical systems (MEMS) radio -frequency (RF) switches. The system would include the following sensing-and-computing subsystems: a) An optical photogrammetric subsystem built around two cameras would estimate geometric distortions of the main reflector; b) A second subsystem would estimate wavefront distortions from amplitudes and phases of signals received by the array feed elements; and c) A third subsystem, built around small probes on the subreflector plane, would estimate wavefront distortions from differences among phases of signals received by the probes. The distortion estimates from the three subsystems would be processed to generate control signals to be fed to the MEMS RF switches to correct for the distortions, thereby enabling collimation and aiming of the received or transmitted radio beam to the required precision.

Terahertz adaptive optics with a deformable mirror.

PubMed

Brossard, Mathilde; Sauvage, Jean-François; Perrin, Mathias; Abraham, Emmanuel

2018-04-01

We report on the wavefront correction of a terahertz (THz) beam using adaptive optics, which requires both a wavefront sensor that is able to sense the optical aberrations, as well as a wavefront corrector. The wavefront sensor relies on a direct 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. By measuring the phase variation of the THz electric field in the crystal, we were able to minimize the geometrical aberrations of the beam, thanks to the action of a deformable mirror. This phase control will open the route to THz adaptive optics in order to optimize the THz beam quality for both practical and fundamental applications.

Common-Path Interferometric Wavefront Sensing for Space Telescopes

NASA Technical Reports Server (NTRS)

Wallace, James Kent

2011-01-01

This paper presents an optical configuration for a common-path phase-shifting interferometric wavefront sensor.1 2 This sensor has a host of attractive features which make it well suited for space-based adaptive optics. First, it is strictly reflective and therefore operates broadband, second it is common mode and therefore does not suffer from systematic errors (like vibration) that are typical in other interferometers, third it is a phase-shifting interferometer and therefore benefits from both the sensitivity of interferometric sensors as well as the noise rejection afforded by synchronous detection. Unlike the Shack-Hartman wavefront sensor, it has nearly uniform sensitivity to all pupil modes. Optical configuration, theory and simulations for such a system will be discussed along with predicted performance.

Photonic Doppler velocimetry probe designed with stereo imaging

NASA Astrophysics Data System (ADS)

Malone, Robert M.; Cata, Brian M.; Daykin, Edward P.; Esquibel, David L.; Frogget, Brent C.; Holtkamp, David B.; Kaufman, Morris I.; McGillivray, Kevin D.; Palagi, Martin J.; Pazuchanics, Peter; Romero, Vincent T.; Sorenson, Danny S.

2014-09-01

During the fabrication of an aspherical mirror, the inspection of the residual wavefront error is critical. In the program of a spaceborne telescope development, primary mirror is made of ZERODUR with clear aperture of 450 mm. The mass is 10 kg after lightweighting. Deformation of mirror due to gravity is expected; hence uniform supporting measured by load cells has been applied to reduce the gravity effect. Inspection has been taken to determine the residual wavefront error at the configuration of mirror face upwards. Correction polishing has been performed according to the measurement. However, after comparing with the data measured by bench test while the primary mirror is at a configuration of mirror face horizontal, deviations have been found for the two measurements. Optical system that is not able to meet the requirement is predicted according to the measured wavefront error by bench test. A target wavefront error of secondary mirror is therefore analyzed to correct that of primary mirror. Optical performance accordingly is presented.

Phase shifting interferometer

DOEpatents

Sommargren, Gary E.

1999-01-01

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. Whereas current interferometers illuminate the optic to be tested with an aberrated wavefront which also limits the accuracy of the measurement, this interferometer uses an essentially perfect spherical measurement wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Phase shifting interferometer

DOEpatents

Sommargren, G.E.

1999-08-03

An interferometer is disclosed which has the capability of measuring optical elements and systems with an accuracy of {lambda}/1000 where {lambda} is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about {lambda}/50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. Whereas current interferometers illuminate the optic to be tested with an aberrated wavefront which also limits the accuracy of the measurement, this interferometer uses an essentially perfect spherical measurement wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms. 11 figs.

Non-common path aberration correction in an adaptive optics scanning ophthalmoscope

PubMed Central

Sulai, Yusufu N.; Dubra, Alfredo

2014-01-01

The correction of non-common path aberrations (NCPAs) between the imaging and wavefront sensing channel in a confocal scanning adaptive optics ophthalmoscope is demonstrated. NCPA correction is achieved by maximizing an image sharpness metric while the confocal detection aperture is temporarily removed, effectively minimizing the monochromatic aberrations in the illumination path of the imaging channel. Comparison of NCPA estimated using zonal and modal orthogonal wavefront corrector bases provided wavefronts that differ by ~λ/20 in root-mean-squared (~λ/30 standard deviation). Sequential insertion of a cylindrical lens in the illumination and light collection paths of the imaging channel was used to compare image resolution after changing the wavefront correction to maximize image sharpness and intensity metrics. Finally, the NCPA correction was incorporated into the closed-loop adaptive optics control by biasing the wavefront sensor signals without reducing its bandwidth. PMID:25401020

Optical-beam wavefront control based on the atmospheric backscatter signal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banakh, V A; Razenkov, I A; Rostov, A P

2015-02-28

The feasibility of compensating for aberrations of the optical-beam initial wavefront by aperture sounding, based on the atmospheric backscatter signal from an additional laser source with a different wavelength, is experimentally studied. It is shown that the adaptive system based on this principle makes it possible to compensate for distortions of the initial beam wavefront on a surface path in atmosphere. Specifically, the beam divergence decreases, while the level of the detected mean backscatter power from the additional laser source increases. (light scattering)

Clinical Outcomes of SMILE With a Triple Centration Technique and Corneal Wavefront-Guided Transepithelial PRK in High Astigmatism.

PubMed

Jun, Ikhyun; Kang, David Sung Yong; Reinstein, Dan Z; Arba-Mosquera, Samuel; Archer, Timothy J; Seo, Kyoung Yul; Kim, Tae-Im

2018-03-01

To comparatively investigate the clinical outcomes, vector parameters, and corneal aberrations of small incision lenticule extraction (SMILE) with a triple centration technique and corneal wavefront-guided transepithelial photorefractive keratectomy (PRK) for the correction of high astigmatism. This retrospective, comparative case series study included 89 eyes (89 patients) that received treatment for myopia with high astigmatism (≥ 2.50 diopters) using SMILE with a triple centration technique (SMILE group; 45 eyes) and corneal wavefront-guided transepithelial PRK (transepithelial PRK group; 44 eyes). Visual acuity measurement, manifest refraction, slit-lamp examination, autokeratometry, corneal topography, and evaluation of corneal wavefront aberration were performed preoperatively and at 1, 3, and 6 months after surgery. The safety, efficacy, vector parameters, and corneal aberrations at 6 months after surgery were compared between the two groups. At 6 months after surgery, the transepithelial PRK and SMILE groups exhibited comparable mean uncorrected distance visual acuities (-0.06 ± 0.07 and -0.05 ± 0.07 logMAR, respectively), safety, efficacy, and predictability of refractive and visual outcomes. There was a slight but statistically significant difference in the correction index between the transepithelial PRK and SMILE groups (0.96 ± 0.11 and 0.91 ± 0.10, respectively). Whereas the transepithelial PRK group exhibited increased corneal spherical aberration and significantly reduced corneal coma and trefoil, no changes in aberrometric values were noted in the SMILE group. Both SMILE with a triple centration technique and corneal wavefront-guided transepithelial PRK are effective and provide predictable outcomes for the correction of high myopic astigmatism, although slight undercorrection was observed in the SMILE group. The triple centration technique was helpful in astigmatism correction by SMILE. [J Refract Surg. 2018;34(3):156-163.]. Copyright 2018, SLACK Incorporated.

James Webb Space Telescope optical simulation testbed III: first experimental results with linear-control alignment

NASA Astrophysics Data System (ADS)

Egron, Sylvain; Lajoie, Charles-Philippe; Leboulleux, Lucie; N'Diaye, Mamadou; Pueyo, Laurent; Choquet, Élodie; Perrin, Marshall D.; Ygouf, Marie; Michau, Vincent; Bonnefois, Aurélie; Fusco, Thierry; Escolle, Clément; Ferrari, Marc; Hugot, Emmanuel; Soummer, Rémi

2016-07-01

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to study wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science and Operations Center. The design of JOST reproduces the physics of JWST's three-mirror anastigmat (TMA) using three custom aspheric lenses. It provides similar quality image as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at 633 nm. An Iris AO segmented mirror stands for the segmented primary mirror of JWST. Actuators allow us to control (1) the 18 segments of the segmented mirror in piston, tip, tilt and (2) the second lens, which stands for the secondary mirror, in tip, tilt and x, y, z positions. We present the full linear control alignment infrastructure developed for JOST, with an emphasis on multi-field wavefront sensing and control. Our implementation of the Wavefront Sensing (WFS) algorithms using phase diversity is experimentally tested. The wavefront control (WFC) algorithms, which rely on a linear model for optical aberrations induced by small misalignments of the three lenses, are tested and validated on simulations.

Closed-loop adaptive optic comparison between a Shack-Hartmann and a distorted grating wavefront sensor

NASA Astrophysics Data System (ADS)

Harrison, Paul; Erry, Gavin R. G.; Otten, Leonard J.; Cuevas, Desirae M.; Weaver, Lawrence D.

2004-11-01

Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL's ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.

Closed-loop adaptive optic comparison between a Shack-Hartmann and a distorted-grating wavefront sensor

NASA Astrophysics Data System (ADS)

Harrison, Paul; Erry, Gavin R. G.; Otten, Leonard J., III; Cuevas, D. M.; Weaver, Lawrence D.

2004-02-01

Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL"s ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.

Rapid and highly integrated FPGA-based Shack-Hartmann wavefront sensor for adaptive optics system

NASA Astrophysics Data System (ADS)

Chen, Yi-Pin; Chang, Chia-Yuan; Chen, Shean-Jen

2018-02-01

In this study, a field programmable gate array (FPGA)-based Shack-Hartmann wavefront sensor (SHWS) programmed on LabVIEW can be highly integrated into customized applications such as adaptive optics system (AOS) for performing real-time wavefront measurement. Further, a Camera Link frame grabber embedded with FPGA is adopted to enhance the sensor speed reacting to variation considering its advantage of the highest data transmission bandwidth. Instead of waiting for a frame image to be captured by the FPGA, the Shack-Hartmann algorithm are implemented in parallel processing blocks design and let the image data transmission synchronize with the wavefront reconstruction. On the other hand, we design a mechanism to control the deformable mirror in the same FPGA and verify the Shack-Hartmann sensor speed by controlling the frequency of the deformable mirror dynamic surface deformation. Currently, this FPGAbead SHWS design can achieve a 266 Hz cyclic speed limited by the camera frame rate as well as leaves 40% logic slices for additionally flexible design.

On-Orbit Multi-Field Wavefront Control with a Kalman Filter

NASA Technical Reports Server (NTRS)

Lou, John; Sigrist, Norbert; Basinger, Scott; Redding, David

2008-01-01

A document describes a multi-field wavefront control (WFC) procedure for the James Webb Space Telescope (JWST) on-orbit optical telescope element (OTE) fine-phasing using wavefront measurements at the NIRCam pupil. The control is applied to JWST primary mirror (PM) segments and secondary mirror (SM) simultaneously with a carefully selected ordering. Through computer simulations, the multi-field WFC procedure shows that it can reduce the initial system wavefront error (WFE), as caused by random initial system misalignments within the JWST fine-phasing error budget, from a few dozen micrometers to below 50 nm across the entire NIRCam Field of View, and the WFC procedure is also computationally stable as the Monte-Carlo simulations indicate. With the incorporation of a Kalman Filter (KF) as an optical state estimator into the WFC process, the robustness of the JWST OTE alignment process can be further improved. In the presence of some large optical misalignments, the Kalman state estimator can provide a reasonable estimate of the optical state, especially for those degrees of freedom that have a significant impact on the system WFE. The state estimate allows for a few corrections to the optical state to push the system towards its nominal state, and the result is that a large part of the WFE can be eliminated in this step. When the multi-field WFC procedure is applied after Kalman state estimate and correction, the stability of fine-phasing control is much more certain. Kalman Filter has been successfully applied to diverse applications as a robust and optimal state estimator. In the context of space-based optical system alignment based on wavefront measurements, a KF state estimator can combine all available wavefront measurements, past and present, as well as measurement and actuation error statistics to generate a Maximum-Likelihood optimal state estimator. The strength and flexibility of the KF algorithm make it attractive for use in real-time optical system alignment when WFC alone cannot effectively align the system.

Testbed Demonstration of Low Order Wavefront Sensing and Control Technology for WFIRST Coronagraph

NASA Astrophysics Data System (ADS)

Shi, Fang; Balasubramanian, K.; Cady, E.; Kern, B.; Lam, R.; Mandic, M.; Patterson, K.; Poberezhskiy, I.; Shields, J.; Seo, J.; Tang, H.; Truong, T.; Wilson, D.

2017-01-01

NASA’s WFIRST-AFTA Coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. To maintain the required coronagraph performance in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C will use the rejected stellar light to sense and suppress the telescope pointing drift and jitter as well as low order wavefront errors due to the changes in thermal loading of the telescope and the rest of the observatory. The LOWFS/C uses a Zernike phase contrast wavefront sensor with the phase shifting disk combined with the stellar light rejecting occulting mask, a key concept to minimize the non-common path error. Developed as a part of the Dynamic High Contrast Imaging Testbed (DHCIT), the LOWFS/C subsystem also consists of an Optical Telescope Assembly Simulator (OTA-S) to generate the realistic line-of-sight (LoS) drift and jitter as well as low order wavefront error from WFIRST-AFTA telescope’s vibration and thermal drift. The entire LOWFS/C subsystem have been integrated, calibrated, and tested in the Dynamic High Contrast Imaging Testbed. In this presentation we will show the results of LOWFS/C performance during the dynamic coronagraph tests in which we have demonstrated that LOWFS/C is able to maintain the coronagraph contrast with the presence of WFIRST like line-of-sight drift and jitter as well as low order wavefront drifts.

SCExAO: First Results and On-Sky Performance

NASA Astrophysics Data System (ADS)

Currie, Thayne; Guyon, Olivier; Martinache, Frantz; Clergeon, Christophe; McElwain, Michael; Thalmann, Christian; Jovanovic, Nemanja; Singh, Garima; Kudo, Tomoyuki

2014-01-01

We present new on-sky results for the Subaru Coronagraphic Extreme Adaptive Optics imager (SCExAO) verifying and quantifying the contrast gain enabled by key components: the closed-loop coronagraphic low-order wavefront sensor (CLOWFS) and focal plane wavefront control (``speckle nulling''). SCExAO will soon be coupled with a high-order, Pyramid wavefront sensor which will yield > 90% Strehl ratio and enable 106-107 contrast at small angular separations allowing us to image gas giant planets at solar system scales. Upcoming instruments like VAMPIRES, FIRST, and CHARIS will expand SCExAO's science capabilities.

Analysis and experimental demonstration of conformal adaptive phase-locked fiber array for laser communications and beam projection applications

NASA Astrophysics Data System (ADS)

Liu, Ling

The primary goal of this research is the analysis, development, and experimental demonstration of an adaptive phase-locked fiber array system for free-space optical communications and laser beam projection applications. To our knowledge, the developed adaptive phase-locked system composed of three fiber collimators (subapertures) with tip-tilt wavefront phase control at each subaperture represents the first reported fiber array system that implements both phase-locking control and adaptive wavefront tip-tilt control capabilities. This research has also resulted in the following innovations: (a) The first experimental demonstration of a phase-locked fiber array with tip-tilt wave-front aberration compensation at each fiber collimator; (b) Development and demonstration of the fastest currently reported stochastic parallel gradient descent (SPGD) system capable of operation at 180,000 iterations per second; (c) The first experimental demonstration of a laser communication link based on a phase-locked fiber array; (d) The first successful experimental demonstration of turbulence and jitter-induced phase distortion compensation in a phase-locked fiber array optical system; (e) The first demonstration of laser beam projection onto an extended target with a randomly rough surface using a conformal adaptive fiber array system. Fiber array optical systems, the subject of this study, can overcome some of the draw-backs of conventional monolithic large-aperture transmitter/receiver optical systems that are usually heavy, bulky, and expensive. The primary experimental challenges in the development of the adaptive phased-locked fiber-array included precise (<5 microrad) alignment of the fiber collimators and development of fast (100kHz-class) phase-locking and wavefront tip-tilt control systems. The precise alignment of the fiber collimator array is achieved through a specially developed initial coarse alignment tool based on high precision piezoelectric picomotors and a dynamic fine alignment mechanism implemented with specially designed and manufactured piezoelectric fiber positioners. Phase-locking of the fiber collimators is performed by controlling the phases of the output beams (beamlets) using integrated polarization-maintaining (PM) fiber-coupled LiNbO3 phase shifters. The developed phase-locking controllers are based on either the SPGD algorithm or the multi-dithering technique. Subaperture wavefront phase tip-tilt control is realized using piezoelectric fiber positioners that are controlled using a computer-based SPGD controller. Both coherent (phase-locked) and incoherent beam combining in the fiber array system are analyzed theoretically and experimentally. Two special fiber-based beam-combining testbeds have been built to demonstrate the technical feasibility of phase-locking compensation prior to free-space operation. In addition, the reciprocity of counter-propagating beams in a phase-locked fiber array system has been investigated. Coherent beam combining in a phase-locking system with wavefront phase tip-tilt compensation at each subaperture is successfully demonstrated when laboratory-simulated turbulence and wavefront jitters are present in the propagation path of the beamlets. In addition, coherent beam combining with a non-cooperative extended target in the control loop is successfully demonstrated.

Robust Wave-front Correction in a Small Scale Adaptive Optics System Using a Membrane Deformable Mirror

NASA Astrophysics Data System (ADS)

Choi, Y.; Park, S.; Baik, S.; Jung, J.; Lee, S.; Yoo, J.

A small scale laboratory adaptive optics system using a Shack-Hartmann wave-front sensor (WFS) and a membrane deformable mirror (DM) has been built for robust image acquisition. In this study, an adaptive limited control technique is adopted to maintain the long-term correction stability of an adaptive optics system. To prevent the waste of dynamic correction range for correcting small residual wave-front distortions which are inefficient to correct, the built system tries to limit wave-front correction when a similar small difference wave-front pattern is repeatedly generated. Also, the effect of mechanical distortion in an adaptive optics system is studied and a pre-recognition method for the distortion is devised to prevent low-performance system operation. A confirmation process for a balanced work assignment among deformable mirror (DM) actuators is adopted for the pre-recognition. The corrected experimental results obtained by using a built small scale adaptive optics system are described in this paper.

Distributed wavefront reconstruction with SABRE for real-time large scale adaptive optics control

NASA Astrophysics Data System (ADS)

Brunner, Elisabeth; de Visser, Cornelis C.; Verhaegen, Michel

2014-08-01

We present advances on Spline based ABerration REconstruction (SABRE) from (Shack-)Hartmann (SH) wavefront measurements for large-scale adaptive optics systems. SABRE locally models the wavefront with simplex B-spline basis functions on triangular partitions which are defined on the SH subaperture array. This approach allows high accuracy through the possible use of nonlinear basis functions and great adaptability to any wavefront sensor and pupil geometry. The main contribution of this paper is a distributed wavefront reconstruction method, D-SABRE, which is a 2 stage procedure based on decomposing the sensor domain into sub-domains each supporting a local SABRE model. D-SABRE greatly decreases the computational complexity of the method and removes the need for centralized reconstruction while obtaining a reconstruction accuracy for simulated E-ELT turbulences within 1% of the global method's accuracy. Further, a generalization of the methodology is proposed making direct use of SH intensity measurements which leads to an improved accuracy of the reconstruction compared to centroid algorithms using spatial gradients.

Wavefront sensor-driven variable-geometry pupil for ground-based aperture synthesis imaging

NASA Astrophysics Data System (ADS)

Tyler, David W.

2000-07-01

I describe a variable-geometry pupil (VGP) to increase image resolution for ground-based near-IR and optical imaging. In this scheme, a curvature-type wavefront sensor provides an estimate of the wavefront curvature to the controller of a high-resolution spatial light modulator (SLM) or micro- electromechanical (MEM) mirror, positioned at an image of the telescope pupil. This optical element, the VGP, passes or reflects the incident beam only where the wavefront phase is sufficiently smooth, viz., where the curvature is sufficiently low. Using a computer simulation, I show the VGP can sharpen and smooth the long-exposure PSF and increase the OTF SNR for tilt-only and low-order AO systems, allowing higher resolution and more stable deconvolution with dimmer AO guidestars.

Coherent control of plasma dynamics by feedback-optimized wavefront manipulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Z.-H.; Hou, B.; Gao, G.

2015-05-15

Plasmas generated by an intense laser pulse can support coherent structures such as large amplitude wakefield that can affect the outcome of an experiment. We investigate the coherent control of plasma dynamics by feedback-optimized wavefront manipulation using a deformable mirror. The experimental outcome is directly used as feedback in an evolutionary algorithm for optimization of the phase front of the driving laser pulse. In this paper, we applied this method to two different experiments: (i) acceleration of electrons in laser driven plasma waves and (ii) self-compression of optical pulses induced by ionization nonlinearity. The manipulation of the laser wavefront leadsmore » to orders of magnitude improvement to electron beam properties such as the peak charge, beam divergence, and transverse emittance. The demonstration of coherent control for plasmas opens new possibilities for future laser-based accelerators and their applications.« less

The relationship between decorrelation time and sample thickness in acute rat brain tissue slices (Conference Presentation)

NASA Astrophysics Data System (ADS)

Brake, Joshua; Jang, Mooseok; Yang, Changhuei

2016-03-01

The optical opacity of biological tissue has long been a challenge in biomedical optics due to the strong scattering nature of tissue in the optical regime. While most conventional optical techniques attempt to gate out multiply scattered light and use only unscattered light, new approaches in the field of wavefront shaping exploit the time reversible symmetry of optical scattering in order to focus light inside or through scattering media. While these approaches have been demonstrated effectively on static samples, it has proven difficult to apply them to dynamic biological samples since even small changes in the relative positions of the scatterers within will cause the time symmetry that wavefront shaping relies upon to decorrelate. In this paper we investigate the decorrelation curves of acute rat brain slices for thicknesses in the range 1-3 mm (1/e decorrelation time on the order of seconds) using multi-speckle diffusing wave spectroscopy (MSDWS) and compare the results with theoretical predictions. The results of this study demonstrate that the 1/L^2 relationship between decorrelation time and thickness predicted by diffusing wave spectroscopy provides a good rule of thumb for estimating how the decorrelation of a sample will change with increasing thickness. Understanding this relationship will provide insight to guide the future development of biophotonic wavefront shaping tools by giving an estimate of how fast wavefront shaping systems need to operate to overcome the dynamic nature of biological samples.

Hybrid wavefront sensing and image correction algorithm for imaging through turbulent media

NASA Astrophysics Data System (ADS)

Wu, Chensheng; Robertson Rzasa, John; Ko, Jonathan; Davis, Christopher C.

2017-09-01

It is well known that passive image correction of turbulence distortions often involves using geometry-dependent deconvolution algorithms. On the other hand, active imaging techniques using adaptive optic correction should use the distorted wavefront information for guidance. Our work shows that a hybrid hardware-software approach is possible to obtain accurate and highly detailed images through turbulent media. The processing algorithm also takes much fewer iteration steps in comparison with conventional image processing algorithms. In our proposed approach, a plenoptic sensor is used as a wavefront sensor to guide post-stage image correction on a high-definition zoomable camera. Conversely, we show that given the ground truth of the highly detailed image and the plenoptic imaging result, we can generate an accurate prediction of the blurred image on a traditional zoomable camera. Similarly, the ground truth combined with the blurred image from the zoomable camera would provide the wavefront conditions. In application, our hybrid approach can be used as an effective way to conduct object recognition in a turbulent environment where the target has been significantly distorted or is even unrecognizable.

Linear dark field control: simulation for implementation and testing on the UA wavefront control testbed

NASA Astrophysics Data System (ADS)

Miller, Kelsey; Guyon, Olivier

2016-07-01

This paper presents the early-stage simulation results of linear dark field control (LDFC) as a new approach to maintaining a stable dark hole within a stellar post-coronagraphic PSF. In practice, conventional speckle nulling is used to create a dark hole in the PSF, and LDFC is then employed to maintain the dark field by using information from the bright speckle field. The concept exploits the linear response of the bright speckle intensity to wavefront variations in the pupil, and therefore has many advantages over conventional speckle nulling as a method for stabilizing the dark hole. In theory, LDFC is faster, more sensitive, and more robust than using conventional speckle nulling techniques, like electric field conjugation, to maintain the dark hole. In this paper, LDFC theory, linear bright speckle characterization, and first results in simulation are presented as an initial step toward the deployment of LDFC on the UA Wavefront Control testbed in the coming year.

The low-order wavefront control system for the PICTURE-C mission: preliminary testbed results from the Shack-Hartmann sensor

NASA Astrophysics Data System (ADS)

Howe, Glenn A.; Mendillo, Christopher B.; Hewawasam, Kuravi; Martel, Jason; Finn, Susanna C.; Cook, Timothy A.; Chakrabarti, Supriya

2017-09-01

The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around three nearby stars from a high-altitude balloon using a vector vortex coronagraph. We present experimental results of the PICTURE-C low-order wavefront control (LOWFC) system utilizing a Shack-Hartmann (SH) sensor in an instrument testbed. The SH sensor drives both the alignment of the telescope secondary mirror using a 6-axis Hexapod and a surface parallel array deformable mirror to remove residual low-order aberrations. The sensor design and actuator calibration methods are discussed and the preliminary LOWFC closed-loop performance is shown to stabilize a reference wavefront to an RMS error of 0.30 +/- 0.29 nm.

Safety and efficacy of wavefront-guided myopic laser in situ keratomileusis using a new wavefront sensor technology: first 100 cases.

PubMed

Smadja, David; Santhiago, Marcony R; Tellouck, Joy; De Castro, Tania; Lecomte, Fanny; Mello, Glauco R; Touboul, David

2015-08-01

To evaluate the safety and efficacy of wavefront-guided laser in situ keratomileusis (LASIK) for the correction of low to high myopia and myopic astigmatism using data derived from a new-generation Hartmann-Shack aberrometer. Refractive Surgery Unit, Bordeaux Hospital University, France. Retrospective case series. This retrospective study analyzed the initial group of eyes treated with wavefront-guided LASIK for myopia and myopic astigmatism using the Visx S4IR excimer laser and wavefront data derived from a new Hartmann-Shack aberrometer (iDesign Advanced Wavescan aberrometer). Refractive (refraction and refractive accuracy) and visual outcomes (uncorrected [UDVA] and corrected [CDVA] distance visual acuities) were recorded 3 months postoperatively. The study included 100 eyes of 50 consecutively treated patients. The mean decimal UDVA improved from 0.1 ± 0.1 (SD) preoperatively to 1.1 ± 0.15 postoperatively (P < .01). A monocular UDVA of 20/16, 20/20, and 20/25 were achieved in 76.6%, 94.4%, and 96.6% of eyes, respectively. The postoperative manifest spherical equivalent was within ±0.5 diopter in all eyes. No eye lost 2 or more lines of CDVA, and 29.2% of the eyes gained 1 or more lines of CDVA. Wavefront-guided LASIK performed using data derived from the new Hartmann-Shack aberrometer was safe, effective, and predictable for treating myopia and myopic astigmatism. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Multigrid preconditioned conjugate-gradient method for large-scale wave-front reconstruction.

PubMed

Gilles, Luc; Vogel, Curtis R; Ellerbroek, Brent L

2002-09-01

We introduce a multigrid preconditioned conjugate-gradient (MGCG) iterative scheme for computing open-loop wave-front reconstructors for extreme adaptive optics systems. We present numerical simulations for a 17-m class telescope with n = 48756 sensor measurement grid points within the aperture, which indicate that our MGCG method has a rapid convergence rate for a wide range of subaperture average slope measurement signal-to-noise ratios. The total computational cost is of order n log n. Hence our scheme provides for fast wave-front simulation and control in large-scale adaptive optics systems.

SCExAO: First Results and On-Sky Performance

NASA Technical Reports Server (NTRS)

Currie, Thayne; Guyon, Olivier; Martinache, Frantz; Clergeon, Christophe; McElwain, Michael; Thalmann, Christian; Jovanovic, Nemanja; Singh, Garima; Kudo, Tomoyuki

2013-01-01

We present new on-sky results for the Subaru Coronagraphic Extreme Adaptive Optics imager (SCExAO) verifying and quantifying the contrast gain enabled by key components: the closed-loop coronagraphic low-order wavefront sensor (CLOWFS) and focal plane wavefront control ("speckle nulling"). SCExAO will soon be coupled with a high-order, Pyramid wavefront sensor which will yield greater than 90% Strehl ratio and enable 10(exp 6) -10(exp 7) contrast at small angular separations allowing us to image gas giant planets at solar system scales. Upcoming instruments like VAMPIRES, FIRST, and CHARIS will expand SCExAO's science capabilities.

Electrowetting lenses for compensating phase and curvature distortion in arrayed laser systems.

PubMed

Niederriter, Robert D; Watson, Alexander M; Zahreddine, Ramzi N; Cogswell, Carol J; Cormack, Robert H; Bright, Victor M; Gopinath, Juliet T

2013-05-10

We have demonstrated a one-dimensional array of individually addressable electrowetting tunable liquid lenses that compensate for more than one wave of phase distortion across a wavefront. We report a scheme for piston control using tunable liquid lens arrays in volume-bound cavities that alter the optical path length without affecting the wavefront curvature. Liquid lens arrays with separately tunable focus or phase control hold promise for laser communication systems and adaptive optics.

DeMi Payload Progress Update and Adaptive Optics (AO) Control Comparisons – Meeting Space AO Requirements on a CubeSat

NASA Astrophysics Data System (ADS)

Grunwald, Warren; Holden, Bobby; Barnes, Derek; Allan, Gregory; Mehrle, Nicholas; Douglas, Ewan S.; Cahoy, Kerri

2018-01-01

The Deformable Mirror (DeMi) CubeSat mission utilizes an Adaptive Optics (AO) control loop to correct incoming wavefronts as a technology demonstration for space-based imaging missions, such as high contrast observations (Earthlike exoplanets) and steering light into core single mode fibers for amplification. While AO has been used extensively on ground based systems to correct for atmospheric aberrations, operating an AO system on-board a small satellite presents different challenges. The DeMi payload 140 actuator MEMS deformable mirror (DM) corrects the incoming wavefront in four different control modes: 1) internal observation with a Shack-Hartmann Wavefront Sensor (SHWFS), 2) internal observation with an image plane sensor, 3) external observation with a SHWFS, and 4) external observation with an image plane sensor. All modes have wavefront aberration from two main sources, time-invariant launch disturbances that have changed the optical path from the expected path when calibrated in the lab and very low temporal frequency thermal variations as DeMi orbits the Earth. The external observation modes has additional error from: the pointing precision error from the attitude control system and reaction wheel jitter. Updates on DeMi’s mechanical, thermal, electrical, and mission design are also presented. The analysis from the DeMi payload simulations and testing provides information on the design options when developing space-based AO systems.

Prediction of subsurface fracture in mining zone of Papua using passive seismic tomography based on Fresnel zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Setiadi, Herlan; Nurhandoko, Bagus Endar B.; Wely, Woen

Fracture prediction in a block cave of underground mine is very important to monitor the structure of the fracture that can be harmful to the mining activities. Many methods can be used to obtain such information, such as TDR (Time Domain Relectometry) and open hole. Both of them have limitations in range measurement. Passive seismic tomography is one of the subsurface imaging method. It has advantage in terms of measurements, cost, and rich of rock physical information. This passive seismic tomography studies using Fresnel zone to model the wavepath by using frequency parameter. Fresnel zone was developed by Nurhandoko inmore » 2000. The result of this study is tomography of P and S wave velocity which can predict position of fracture. The study also attempted to use sum of the wavefronts to obtain position and time of seismic event occurence. Fresnel zone tomography and the summation wavefront can predict location of geological structure of mine area as well.« less

High speed real-time wavefront processing system for a solid-state laser system

NASA Astrophysics Data System (ADS)

Liu, Yuan; Yang, Ping; Chen, Shanqiu; Ma, Lifang; Xu, Bing

2008-03-01

A high speed real-time wavefront processing system for a solid-state laser beam cleanup system has been built. This system consists of a core2 Industrial PC (IPC) using Linux and real-time Linux (RT-Linux) operation system (OS), a PCI image grabber, a D/A card. More often than not, the phase aberrations of the output beam from solid-state lasers vary fast with intracavity thermal effects and environmental influence. To compensate the phase aberrations of solid-state lasers successfully, a high speed real-time wavefront processing system is presented. Compared to former systems, this system can improve the speed efficiently. In the new system, the acquisition of image data, the output of control voltage data and the implementation of reconstructor control algorithm are treated as real-time tasks in kernel-space, the display of wavefront information and man-machine conversation are treated as non real-time tasks in user-space. The parallel processing of real-time tasks in Symmetric Multi Processors (SMP) mode is the main strategy of improving the speed. In this paper, the performance and efficiency of this wavefront processing system are analyzed. The opened-loop experimental results show that the sampling frequency of this system is up to 3300Hz, and this system can well deal with phase aberrations from solid-state lasers.

Effect of Pupil Size on Wavefront Refraction during Orthokeratology.

PubMed

Faria-Ribeiro, Miguel; Navarro, Rafael; González-Méijome, José Manuel

2016-11-01

It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology, might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical quality after orthokeratology, using ray tracing software for different pupil sizes. Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm pupil diameters. The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm. The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more significant under low illumination levels.

Low-order wavefront sensing for coronagraphic telescopes

NASA Astrophysics Data System (ADS)

Subedi, Hari; Kasdin, Jeremy; Peter Varnai

2018-01-01

Space telescopes equipped with a coronagraph to detect and characterize exoplanets must have the ability to sense and control low-order wavefront aberrations. Most concepts for low-order wavefront sensing use the starlight rejected by the coronagraph to sense these aberrations. The sensor must be able to make precise estimates and be robust to photon and read noise. A thorough study of various differential low-order wavefront sensors (LOWFSs) would be beneficial for future space-based observatories designed for exoplanet detection and characterization. In this talk, we will expand on the comparison of different LOWFSs that use the rejected starlight either from the coronagraphic focal plane or the Lyot plane to estimate these aberrations. We will also present the experimental results of the sparse aperture mask (SAM) LOWFS that we have designed at the Princeton High Contrast Imaging Lab (PHCIL).

Far field and wavefront characterization of a high-power semiconductor laser for free space optical communications

NASA Technical Reports Server (NTRS)

Cornwell, Donald M., Jr.; Saif, Babak N.

1991-01-01

The spatial pointing angle and far field beamwidth of a high-power semiconductor laser are characterized as a function of CW power and also as a function of temperature. The time-averaged spatial pointing angle and spatial lobe width were measured under intensity-modulated conditions. The measured pointing deviations are determined to be well within the pointing requirements of the NASA Laser Communications Transceiver (LCT) program. A computer-controlled Mach-Zehnder phase-shifter interferometer is used to characterize the wavefront quality of the laser. The rms phase error over the entire pupil was measured as a function of CW output power. Time-averaged measurements of the wavefront quality are also made under intensity-modulated conditions. The measured rms phase errors are determined to be well within the wavefront quality requirements of the LCT program.

Testing the pyramid truth wavefront sensor for NFIRAOS in the lab

NASA Astrophysics Data System (ADS)

Mieda, Etsuko; Rosensteiner, Matthias; van Kooten, Maaike; Veran, Jean-Pierre; Lardiere, Olivier; Herriot, Glen

2016-07-01

For today and future adaptive optics observations, sodium laser guide stars (LGSs) are crucial; however, the LGS elongation problem due to the sodium layer has to be compensated, in particular for extremely large telescopes. In this paper, we describe the concept of truth wavefront sensing as a solution and present its design using a pyramid wavefront sensor (PWFS) to improve NFIRAOS (Narrow Field InfraRed Adaptive Optics System), the first light adaptive optics system for Thirty Meter Telescope. We simulate and test the truth wavefront sensor function under a controlled environment using the HeNOS (Herzberg NFIRAOS Optical Simulator) bench, a scaled-down NFIRAOS bench at NRC-Herzberg. We also touch on alternative pyramid component options because despite recent high demands for PWFSs, we suffer from the lack of pyramid supplies due to engineering difficulties.

Simultaneous calculation of three optical surfaces in the 3D SMS freeform RXI optic

NASA Astrophysics Data System (ADS)

Sorgato, Simone; Chaves, Julio; Mohedano, Rubén.; Hernández, Maikel; Blen, José; Benitez, Pablo; Miñano, Juan C.; Grabovickic, Dejan; Thienpont, Hugo; Duerr, Fabian

2016-09-01

The Freeform RXI collimator is a remarkable example of advanced nonimaging device designed with the 3D Simultaneous Multiple Surface (SMS) Method. In the original design, two (the front refracting surface and the back mirror) of the three optical surfaces of the RXI are calculated simultaneously and one (the cavity surrounding the source) is fixed by the designer. As a result, the RXI perfectly couples two input wavefronts (coming from the edges of the extended LED source) with two output wavefronts (defining the output beam). This allows for LED lamps able to produce controlled intensity distributions, which can and have been successfully applied to demanding applications like high- and low-beams for Automotive Lighting. Nevertheless, current trends in this field are moving towards smaller headlamps with more shape constraints driven by car design. We present an improved version of the 3D RXI in which also the cavity surface is computed during the design, so that there are three freeform surfaces calculated simultaneously and an additional degree of freedom for controlling the light emission: now the RXI can perfectly couple three input wavefronts with three output wavefronts. The enhanced control over ray beams allows for improved light homogeneity and better pattern definition.

An experimental apparatus for diffraction-limited soft x-ray nano-focusing

NASA Astrophysics Data System (ADS)

Merthe, Daniel J.; Goldberg, Kenneth A.; Yashchuk, Valeriy V.; Yuan, Sheng; McKinney, Wayne R.; Celestre, Richard; Mochi, Iacopo; Macdougall, James; Morrison, Gregory Y.; Rakawa, Senajith B.; Anderson, Erik; Smith, Brian V.; Domning, Edward E.; Warwick, Tony; Padmore, Howard

2011-09-01

Realizing the experimental potential of high-brightness, next generation synchrotron and free-electron laser light sources requires the development of reflecting x-ray optics capable of wavefront preservation and high-resolution nano-focusing. At the Advanced Light Source (ALS) beamline 5.3.1, we are developing broadly applicable, high-accuracy, in situ, at-wavelength wavefront measurement techniques to surpass 100-nrad slope measurement accuracy for diffraction-limited Kirkpatrick-Baez (KB) mirrors. The at-wavelength methodology we are developing relies on a series of wavefront-sensing tests with increasing accuracy and sensitivity, including scanning-slit Hartmann tests, grating-based lateral shearing interferometry, and quantitative knife-edge testing. We describe the original experimental techniques and alignment methodology that have enabled us to optimally set a bendable KB mirror to achieve a focused, FWHM spot size of 150 nm, with 1 nm (1.24 keV) photons at 3.7 mrad numerical aperture. The predictions of wavefront measurement are confirmed by the knife-edge testing. The side-profiled elliptically bent mirror used in these one-dimensional focusing experiments was originally designed for a much different glancing angle and conjugate distances. Visible-light long-trace profilometry was used to pre-align the mirror before installation at the beamline. This work demonstrates that high-accuracy, at-wavelength wavefront-slope feedback can be used to optimize the pitch, roll, and mirror-bending forces in situ, using procedures that are deterministic and repeatable.

Validation of a Hartmann-Moiré wavefront sensor with large dynamic range.

PubMed

Wei, Xin; Van Heugten, Tony; Thibos, Larry

2009-08-03

Our goal was to validate the accuracy, repeatability, sensitivity, and dynamic range of a Hartmann-Moiré (HM) wavefront sensor (PixelOptics, Inc.) designed for ophthalmic applications. Testing apparatus injected a 4 mm diameter monochromatic (532 nm) beam of light into the wavefront sensor for measurement. Controlled amounts of defocus and astigmatism were introduced into the beam with calibrated spherical (-20D to + 18D) and cylindrical (-8D to + 8D) lenses. Repeatability was assessed with three repeated measurements within a 2-minute period. Correlation coefficients between mean wavefront measurements (n = 3) and expected wavefront vergence for both sphere and cylinder lenses were >0.999. For spherical lenses, the sensor was accurate to within 0.1D over the range from -20D to + 18D. For cylindrical lenses, the sensor was accurate to within 0.1D over the range from -8D to + 8D. The primary limitation to demonstrating an even larger dynamic range was the increasingly critical requirements for optical alignment. Sensitivity to small changes of vergence was constant over the instrument's full dynamic range. Repeatability of measurements for fixed condition was within 0.01D. The Hartmann-Moiré wavefront sensor measures defocus and astigmatism accurately and repeatedly with good sensitivity over a large dynamic range required for ophthalmic applications.

James Webb Space Telescope optical simulation testbed IV: linear control alignment of the primary segmented mirror

NASA Astrophysics Data System (ADS)

Egron, Sylvain; Soummer, Rémi; Lajoie, Charles-Philippe; Bonnefois, Aurélie; Long, Joseph; Michau, Vincent; Choquet, Elodie; Ferrari, Marc; Leboulleux, Lucie; Levecq, Olivier; Mazoyer, Johan; N'Diaye, Mamadou; Perrin, Marshall; Petrone, Peter; Pueyo, Laurent; Sivaramakrishnan, Anand

2017-09-01

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop experiment designed to study wavefront sensing and control for a segmented space telescope, such as JWST. With the JWST Science and Operations Center co-located at STScI, JOST was developed to provide both a platform for staff training and to test alternate wavefront sensing and control strategies for independent validation or future improvements beyond the baseline operations. The design of JOST reproduces the physics of JWST's three-mirror anastigmat (TMA) using three custom aspheric lenses. It provides similar quality image as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at 633 nm. An Iris AO segmented mirror stands for the segmented primary mirror of JWST. Actuators allow us to control (1) the 18 segments of the segmented mirror in piston, tip, tilt and (2) the second lens, which stands for the secondary mirror, in tip, tilt and x, y, z positions. We present the most recent experimental results for the segmented mirror alignment. Our implementation of the Wavefront Sensing (WFS) algorithms using phase diversity is tested on simulation and experimentally. The wavefront control (WFC) algorithms, which rely on a linear model for optical aberrations induced by misalignment of the secondary lens and the segmented mirror, are tested and validated both on simulations and experimentally. In this proceeding, we present the performance of the full active optic control loop in presence of perturbations on the segmented mirror, and we detail the quality of the alignment correction.

Experimental Verification of Sparse Aperture Mask for Low Order Wavefront Sensing

NASA Astrophysics Data System (ADS)

Subedi, Hari; Kasdin, N. Jeremy

2017-01-01

To directly image exoplanets, future space-based missions are equipped with coronagraphs which manipulate the diffraction of starlight and create regions of high contrast called dark holes. Theoretically, coronagraphs can be designed to achieve the high level of contrast required to image exoplanets, which are billions of times dimmer than their host stars, however the aberrations caused by optical imperfections and thermal fluctuations cause the degradation of contrast in the dark holes. Focal plane wavefront control (FPWC) algorithms using deformable mirrors (DMs) are used to mitigate the quasi-static aberrations caused by optical imperfections. Although the FPWC methods correct the quasi-static aberrations, they are blind to dynamic errors caused by telescope jitter and thermal fluctuations. At Princeton's High Contrast Imaging Lab we have developed a new technique that integrates a sparse aperture mask with the coronagraph to estimate these low-order dynamic wavefront errors. This poster shows the effectiveness of a SAM Low-Order Wavefront Sensor in estimating and correcting these errors via simulation and experiment and compares the results to other methods, such as the Zernike Wavefront Sensor planned for WFIRST.

Optical Modeling Activities for the James Webb Space Telescope (JWST) Project. II; Determining Image Motion and Wavefront Error Over an Extended Field of View with a Segmented Optical System

NASA Technical Reports Server (NTRS)

Howard, Joseph M.; Ha, Kong Q.

2004-01-01

This is part two of a series on the optical modeling activities for JWST. Starting with the linear optical model discussed in part one, we develop centroid and wavefront error sensitivities for the special case of a segmented optical system such as JWST, where the primary mirror consists of 18 individual segments. Our approach extends standard sensitivity matrix methods used for systems consisting of monolithic optics, where the image motion is approximated by averaging ray coordinates at the image and residual wavefront error is determined with global tip/tilt removed. We develop an exact formulation using the linear optical model, and extend it to cover multiple field points for performance prediction at each instrument aboard JWST. This optical model is then driven by thermal and dynamic structural perturbations in an integrated modeling environment. Results are presented.

High-speed adaptive optics for imaging of the living human eye

PubMed Central

Yu, Yongxin; Zhang, Tianjiao; Meadway, Alexander; Wang, Xiaolin; Zhang, Yuhua

2015-01-01

The discovery of high frequency temporal fluctuation of human ocular wave aberration dictates the necessity of high speed adaptive optics (AO) correction for high resolution retinal imaging. We present a high speed AO system for an experimental adaptive optics scanning laser ophthalmoscope (AOSLO). We developed a custom high speed Shack-Hartmann wavefront sensor and maximized the wavefront detection speed based upon a trade-off among the wavefront spatial sampling density, the dynamic range, and the measurement sensitivity. We examined the temporal dynamic property of the ocular wavefront under the AOSLO imaging condition and improved the dual-thread AO control strategy. The high speed AO can be operated with a closed-loop frequency up to 110 Hz. Experiment results demonstrated that the high speed AO system can provide improved compensation for the wave aberration up to 30 Hz in the living human eye. PMID:26368408

Phase shifting diffraction interferometer

DOEpatents

Sommargren, Gary E.

1996-01-01

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Phase shifting diffraction interferometer

DOEpatents

Sommargren, G.E.

1996-08-29

An interferometer which has the capability of measuring optical elements and systems with an accuracy of {lambda}/1000 where {lambda} is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about {lambda}/50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms. 8 figs.

Wnt-regulated dynamics of positional information in zebrafish somitogenesis

PubMed Central

Bajard, Lola; Morelli, Luis G.; Ares, Saúl; Pécréaux, Jacques; Jülicher, Frank; Oates, Andrew C.

2014-01-01

How signaling gradients supply positional information in a field of moving cells is an unsolved question in patterning and morphogenesis. Here, we ask how a Wnt signaling gradient regulates the dynamics of a wavefront of cellular change in a flow of cells during somitogenesis. Using time-controlled perturbations of Wnt signaling in the zebrafish embryo, we changed segment length without altering the rate of somite formation or embryonic elongation. This result implies specific Wnt regulation of the wavefront velocity. The observed Wnt signaling gradient dynamics and timing of downstream events support a model for wavefront regulation in which cell flow plays a dominant role in transporting positional information. PMID:24595291

Differences between wavefront and subjective refraction for infrared light.

PubMed

Teel, Danielle F W; Jacobs, Robert J; Copland, James; Neal, Daniel R; Thibos, Larry N

2014-10-01

To determine the accuracy of objective wavefront refractions for predicting subjective refractions for monochromatic infrared light. Objective refractions were obtained with a commercial wavefront aberrometer (COAS, Wavefront Sciences). Subjective refractions were obtained for 30 subjects with a speckle optometer validated against objective Zernike wavefront refractions on a physical model eye (Teel et al., Design and validation of an infrared Badal optometer for laser speckle, Optom Vis Sci 2008;85:834-42). Both instruments used near-infrared (NIR) radiation (835 nm for COAS, 820 nm for the speckle optometer) to avoid correction for ocular chromatic aberration. A 3-mm artificial pupil was used to reduce complications attributed to higher-order ocular aberrations. For comparison with paraxial (Seidel) and minimum root-mean-square (Zernike) wavefront refractions, objective refractions were also determined for a battery of 29 image quality metrics by computing the correcting lens that optimizes retinal image quality. Objective Zernike refractions were more myopic than subjective refractions for 29 of 30 subjects. The population mean discrepancy was -0.26 diopters (D) (SEM = 0.03 D). Paraxial (Seidel) objective refractions tended to be hyperopically biased (mean discrepancy = +0.20 D, SEM = 0.06 D). Refractions based on retinal image quality were myopically biased for 28 of 29 metrics. The mean bias across all 31 measures was -0.24 D (SEM = 0.03). Myopic bias of objective refractions was greater for eyes with brown irises compared with eyes with blue irises. Our experimental results are consistent with the hypothesis that reflected NIR light captured by the aberrometer originates from scattering sources located posterior to the entrance apertures of cone photoreceptors, near the retinal pigment epithelium. The larger myopic bias for brown eyes suggests that a greater fraction of NIR light is reflected from choroidal melanin in brown eyes compared with blue eyes.

Clinical outcomes of wavefront-guided laser in situ keratomileusis: 6-month follow-up.

PubMed

Aizawa, Daisuke; Shimizu, Kimiya; Komatsu, Mari; Ito, Misae; Suzuki, Masanobu; Ohno, Koji; Uozato, Hiroshi

2003-08-01

To evaluate the clinical outcomes 6 months after wavefront-guided laser in situ keratomileusis (LASIK) for myopia in Japan. Department of Ophthalmology, Sanno Hospital, Tokyo, Japan. This prospective study comprised 22 eyes of 12 patients treated with wavefront-guided LASIK who were available for evaluation at 6 months. The mean patient age was 31.2 years +/- 8.4 (SD) (range 23 to 50 years), and the mean preoperative spherical equivalent refraction was -7.30 +/- 2.72 diopters (D) (range -2.75 to -11.88 D). In all cases, preoperative wavefront analysis was performed with a Hartmann-Shack aberrometer and the Technolas 217z flying-spot excimer laser system (Bausch & Lomb) was used with 1.0 mm and 2.0 mm spot sizes and an active eye tracker with a 120 Hz tracking rate. The clinical outcomes of wavefront-guided LASIK were evaluated in terms of safety, efficacy, predictability, stability, complications, and preoperative and postoperative aberrations. At 6 months, 10 eyes had no change in best spectacle-correct visual acuity and 10 gained 1 or more lines. The safety index was 1.11 and the efficacy index, 0.82. Slight undercorrections were observed in highly myopic eyes. In all eyes, the postoperative refraction tended slightly toward myopia for 3 months and stabilized after that. No complication such as epithelial ingrowth, diffuse lamellar keratitis, or infection was observed. Comparison of the preoperative and postoperative aberrations showed that 2nd-order aberrations decreased and higher-order aberrations increased. In the 3rd order, aberrations increased in the high-myopia group (-6.0 D or worse) and decreased in the low to moderate-myopia group (better than -6.0 D). Wavefront-guided LASIK was a good option for refractive surgery, although a longer follow-up in a larger study is required.

Modelling MEMS deformable mirrors for astronomical adaptive optics

NASA Astrophysics Data System (ADS)

Blain, Celia

As of July 2012, 777 exoplanets have been discovered utilizing mainly indirect detection techniques. The direct imaging of exoplanets is the next goal for astronomers, because it will reveal the diversity of planets and planetary systems, and will give access to the exoplanet's chemical composition via spectroscopy. With this spectroscopic knowledge, astronomers will be able to know, if a planet is terrestrial and, possibly, even find evidence of life. With so much potential, this branch of astronomy has also captivated the general public attention. The direct imaging of exoplanets remains a challenging task, due to (i) the extremely high contrast between the parent star and the orbiting exoplanet and (ii) their small angular separation. For ground-based observatories, this task is made even more difficult, due to the presence of atmospheric turbulence. High Contrast Imaging (HCI) instruments have been designed to meet this challenge. HCI instruments are usually composed of a coronagraph coupled with the full onaxis corrective capability of an Extreme Adaptive Optics (ExAO) system. An efficient coronagraph separates the faint planet's light from the much brighter starlight, but the dynamic boiling speckles, created by the stellar image, make exoplanet detection impossible without the help of a wavefront correction device. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is a high performance HCI instrument developed at Subaru Telescope. The wavefront control system of SCExAO consists of three wavefront sensors (WFS) coupled with a 1024- actuator Micro-Electro-Mechanical-System (MEMS) deformable mirror (DM). MEMS DMs offer a large actuator density, allowing high count DMs to be deployed in small size beams. Therefore, MEMS DMs are an attractive technology for Adaptive Optics (AO) systems and are particularly well suited for HCI instruments employing ExAO technologies. SCExAO uses coherent light modulation in the focal plane introduced by the DM, for both wavefront sensing and correction. In this scheme, the DM is used to introduce known aberrations (speckles in the focal plane), which interfere with existing speckles. By monitoring the interference between the pre-existing speckles and the speckles added deliberately by the DM, it is possible to reconstruct the complex amplitude (amplitude and phase) of the focal plane speckles. Thus, the DM is used for wavefront sensing, in a scheme akin to phase diversity. For SCExAO and other HCI systems using phase diversity, the wavefront compensation is a mix of closed-loop and open-loop control of the DM. The successful implementation of MEMS DMs open-loop control relies on a thorough modelling of the DM response to the control system commands. The work presented in this thesis, motivated by the need to provide accurate DM control for the wavefront control system of SCExAO, was centred around the development of MEMS DM models. This dissertation reports the characterization of MEMS DMs and the development of two efficient modelling approaches. The open-loop performance of both approaches has been investigated. The model providing the best result has been implemented within the SCExAO wavefront control software. Within SCExAO, the model was used to command the DM to create focal plane speckles. The work is now focused on using the model within a full speckle nulling process and on increasing the execution speed to make the model suitable for on-sky operation.

Controlling Light Transmission Through Highly Scattering Media Using Semi-Definite Programming as a Phase Retrieval Computation Method.

PubMed

N'Gom, Moussa; Lien, Miao-Bin; Estakhri, Nooshin M; Norris, Theodore B; Michielssen, Eric; Nadakuditi, Raj Rao

2017-05-31

Complex Semi-Definite Programming (SDP) is introduced as a novel approach to phase retrieval enabled control of monochromatic light transmission through highly scattering media. In a simple optical setup, a spatial light modulator is used to generate a random sequence of phase-modulated wavefronts, and the resulting intensity speckle patterns in the transmitted light are acquired on a camera. The SDP algorithm allows computation of the complex transmission matrix of the system from this sequence of intensity-only measurements, without need for a reference beam. Once the transmission matrix is determined, optimal wavefronts are computed that focus the incident beam to any position or sequence of positions on the far side of the scattering medium, without the need for any subsequent measurements or wavefront shaping iterations. The number of measurements required and the degree of enhancement of the intensity at focus is determined by the number of pixels controlled by the spatial light modulator.

Integrated Approach to Airborne Laser Communication

DTIC Science & Technology

2008-12-01

deformable mirror [66, 69, 80]. Some researchers have proposed complicated wavefront control systems to sense and correct the transmitted signals in real...Sensors at the imaging system or laser transmitter measure how the turbulence affects the beacon. If the differences between the phase effects ( wavefront ...communications are severely affected by clouds, dust, and atmospheric turbulence , causing deep, long fades at the receiver. Ultimately a hybrid

Focal plane based wavefront sensing with random DM probes

NASA Astrophysics Data System (ADS)

Pluzhnik, Eugene; Sirbu, Dan; Belikov, Ruslan; Bendek, Eduardo; Dudinov, Vladimir N.

2017-09-01

An internal coronagraph with an adaptive optical system for wavefront control is being considered for direct imaging of exoplanets with upcoming space missions and concepts, including WFIRST, HabEx, LUVOIR, EXCEDE and ACESat. The main technical challenge associated with direct imaging of exoplanets is to control of both diffracted and scattered light from the star so that even a dim planetary companion can be imaged. For a deformable mirror (DM) to create a dark hole with 10-10 contrast in the image plane, wavefront errors must be accurately measured on the science focal plane detector to ensure a common optical path. We present here a method that uses a set of random phase probes applied to the DM to obtain a high accuracy wavefront estimate even for a dynamically changing optical system. The presented numerical simulations and experimental results show low noise sensitivity, high reliability, and robustness of the proposed approach. The method does not use any additional optics or complex calibration procedures and can be used during the calibration stage of any direct imaging mission. It can also be used in any optical experiment that uses a DM as an active optical element in the layout.

Hybrid Lyot coronagraph for WFIRST: high-contrast broadband testbed demonstration

NASA Astrophysics Data System (ADS)

Seo, Byoung-Joon; Cady, Eric; Gordon, Brian; Kern, Brian; Lam, Raymond; Marx, David; Moody, Dwight; Muller, Richard; Patterson, Keith; Poberezhskiy, Ilya; Mejia Prada, Camilo; Sidick, Erkin; Shi, Fang; Trauger, John; Wilson, Daniel

2017-09-01

Hybrid Lyot Coronagraph (HLC) is one of the two operating modes of the Wide-Field InfraRed Survey Telescope (WFIRST) coronagraph instrument. Since being selected by National Aeronautics and Space Administration (NASA) in December 2013, the coronagraph technology is being matured to Technology Readiness Level (TRL) 6 by 2018. To demonstrate starlight suppression in presence of expecting on-orbit input wavefront disturbances, we have built a dynamic testbed in Jet Propulsion Laboratory (JPL) in 2016. This testbed, named as Occulting Mask Coronagraph (OMC) testbed, is designed analogous to the WFIRST flight instrument architecture: It has both HLC and Shape Pupil Coronagraph (SPC) architectures, and also has the Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to sense and correct the dynamic wavefront disturbances. We present upto-date progress of HLC mode demonstration in the OMC testbed. SPC results will be reported separately. We inject the flight-like Line of Sight (LoS) and Wavefront Error (WFE) perturbation to the OMC testbed and demonstrate wavefront control using two deformable mirrors while the LOWFS/C is correcting those perturbation in our vacuum testbed. As a result, we obtain repeatable convergence below 5 × 10-9 mean contrast with 10% broadband light centered at 550 nm in the 360 degrees dark hole with working angle between 3 λ/D and 9 λ/D. We present the key hardware and software used in the testbed, the performance results and their comparison to model expectations.

Realtime speckle sensing and suppression with project 1640 at Palomar

NASA Astrophysics Data System (ADS)

Vasisht, Gautam; Cady, Eric; Zhai, Chengxing; Lockhart, Thomas; Oppenheimer, Ben

2014-08-01

Palomar's Project 1640 (P1640) is the first stellar coronagraph to regularly use active coronagraphic wavefront control (CWFC). For this it has a hierarchy of offset wavefront sensors (WFS), the most important of which is the higher-order WFS (called CAL), which tracks quasi-static modes between 2-35 cycles-per-aperture. The wavefront is measured in the coronagraph at 0.01 Hz rates, providing slope targets to the upstream Palm 3000 adaptive optics (AO) system. The CWFC handles all non-common path distortions up to the coronagraphic focal plane mask, but does not sense second order modes between the WFSs and the science integral field unit (IFU); these modes determine the system's current limit. We have two CWFC operating modes: (1) P-mode, where we only control phases, generating double-sided darkholes by correcting to the largest controllable spatial frequencies, and (2) E-mode, where we can control amplitudes and phases, generating single-sided dark-holes in specified regions-of-interest. We describe the performance and limitations of both these modes, and discuss the improvements we are considering going forward.

Laboratory simulation of atmospheric turbulence induced optical wavefront distortion

NASA Astrophysics Data System (ADS)

Taylor, Travis Shane

1999-11-01

Many creative approaches have been taken in the past for simulating the effect that atmospheric turbulence has on optical beams. Most of the experimental architectures have been complicated and consisted of many optical elements as well as moving components. These techniques have shown a modicum of success; however, they are not completely controllable or predictable. A benchtop technique for experimentally producing one important effect that atmospheric turbulence has on optical beams (phase distortion) is presented here. The system is completely controllable and predictable while accurately representing the statistical nature of the problem. Previous experimentation in optical processing through turbulent media has demonstrated that optical wavefront distortions can be produced via spatial light modulating (SLM) devices, and most turbulence models and experimental results indicate that turbulence can be represented as a phase fluctuation. The amplitude distributions in the resulting far field are primarily due to propagation of the phase. Operating a liquid crystal television (LCTV) in the ``phase- mostly'' mode, a phase fluctuation type model for turbulence is utilized in the present investigation, and a real-time experiment for demonstrating the effects was constructed. For an optical system to simulate optical wavefront distortions due to atmospheric turbulence, the following are required: (1)An optical element that modulates the phasefront of an optical beam (2)A model and a technique for generating spatially correlated turbulence simulating distributions (3)Hardware and software for displaying and manipulating the information addressing the optical phase modulation device The LCTV is ideal for this application. When operated in the ``phase-mostly'' mode some LCTVs can modulate the phasefront of an optical beam by as much as 2π and an algorithm for generating spatially correlated phase screens can be constructed via mathematical modeling software such as Mathcad[2]. The phase screens can then be manipulated and displayed on the LCTV using a computer with an appropriate framegrabber and software. The present system consists of an Epson liquid crystal television (which was optimized to modulate up to 2π of phase), a Macintosh IIci with a framegrabber card, a QuickTime movie consisting of multiple video frames of two dimensional arrays of spatially correlated grayscale images, and two polarizers. The movie is displayed on the television via the framegrabber, and the polarizers are used to operate the television in a mode that mostly modulates the spatial phase distribution of the optical wavefront. The frames of the movie are created using an accepted turbulence model for spatially correlated variations in index of refraction, and each subsequent frame of the movie is calculated following an accepted model for temporally varying turbulence. The model used for generating spatial functions or ``phase screens'' which simulate turbulence is the well known Kolmogorov model. These ``phase screens'' are then used, employing a Taylor's frozen flow model, to simulate temporally varying turbulence. A single ``phase screen'' is given a random velocity vector between 0 and.55 meters per second to simulate temporally varying turbulence. The system is used to distort optical beams as if the beams had propagated through a long pathlength of wavefront distorting medium, such as the atmosphere.

Predicted optical performance of the high-altitude balloon experiment (HABE) telescope in an adverse thermal environment

NASA Astrophysics Data System (ADS)

Akau, Ronald L.; Givler, Richard C.; Eastman, Daniel R.

1994-07-01

The High-Altitude Balloon Experiment telescope was designed to operate at an ambient temperature of -55 degree(s)C and an altitude of 26 km, using a precooled primary mirror. Although at this altitude the air density is only 1.4 percent of the value at sea level, the temperature gradients within the telescope are high enough to deform the optical wavefront. This problem is considerably lessened by precooling the primary mirror to -35 degree(s)C. This paper describes the application of several codes to determine the range of wavefront deformation during a mission.

Numerical analysis of hybrid adaptive optics system for correcting beacon anisoplanatism and thermal blooming

NASA Astrophysics Data System (ADS)

Belen'kii, Mikhail S.; Rye, Vincent; Runyeon, Hope

2007-09-01

A concept of a Hybrid Wavefront-based Stochastic Parallel Gradient Decent (WSPGD) Adaptive Optics (AO) system for correcting the combined effects of Beacon Anisoplanatism and Thermal Blooming is introduced. This system integrates a conventional phase conjugate (PC) AO system with a WSPGD AO system. It uses on-axis wavefront measurements of a laser return from an extended beacon to generate initial deformable mirror (DM) commands. Since high frequency phase components are removed from the wavefront of a laser return by a low-pass filter effect of an extended beacon, the system also uses off-axis wavefront measurements to provide feedback for a multi-dithering beam control algorithm in order to generate additional DM commands that account for those missing high frequency phase components. Performance of the Hybrid WSPGD AO system was evaluated in simulation using a wave optics code. Numerical analysis was performed for two tactical scenarios that included ranges of L = 2 km and L = 20 km, ratio of aperture diameter to Fried parameter, D/r 0, of up to 15, ratio of beam spot size at the target to isoplanatic angle, θ B/θ 0, of up to 40, and general distortion number characterizing the strength of Thermal Blooming, N d = 50, 75, and 100. A line-of-sight in the corrected beam was stabilized using a target-plane tracker. The simulation results reveal that the Hybrid WSPGD AO system can efficiently correct the effects of Beacon Anisoplanatism and Thermal Blooming, providing improved compensation of Thermal Blooming in the presence of strong turbulence. Simulation results also indicate that the Hybrid WSPGD AO system outperforms a conventional PC AO system, increasing the Strehl ratio by up to 300% in less than 50 iterations. A follow-on laboratory demonstration performed under a separate program confirmed our theoretical predictions.

Optimizing focal plane electric field estimation for detecting exoplanets

NASA Astrophysics Data System (ADS)

Groff, T.; Kasdin, N. J.; Riggs, A. J. E.

Detecting extrasolar planets with angular separations and contrast levels similar to Earth requires a large space-based observatory and advanced starlight suppression techniques. This paper focuses on techniques employing an internal coronagraph, which is highly sensitive to optical errors and must rely on focal plane wavefront control techniques to achieve the necessary contrast levels. To maximize the available science time for a coronagraphic mission we demonstrate an estimation scheme using a discrete time Kalman filter. The state estimate feedback inherent to the filter allows us to minimize the number of exposures required to estimate the electric field. We also show progress including a bias estimate into the Kalman filter to eliminate incoherent light from the estimate. Since the exoplanets themselves are incoherent to the star, this has the added benefit of using the control history to gain certainty in the location of exoplanet candidates as the signal-to-noise between the planets and speckles improves. Having established a purely focal plane based wavefront estimation technique, we discuss a sensor fusion concept where alternate wavefront sensors feedforward a time update to the focal plane estimate to improve robustness to time varying speckle. The overall goal of this work is to reduce the time required for wavefront control on a target, thereby improving the observatory's planet detection performance by increasing the number of targets reachable during the lifespan of the mission.

Close-loop performance of a high precision deflectometry controlled deformable mirror (DCDM) unit for wavefront correction in adaptive optics system

NASA Astrophysics Data System (ADS)

Huang, Lei; Zhou, Chenlu; Zhao, Wenchuan; Choi, Heejoo; Graves, Logan; Kim, Daewook

2017-06-01

We present a high precision deflectometry system (DS) controlled deformable mirror (DM) solution for optical system. Different from wavefront and non-wavefront system, the DS and the DM are set to be an individual integrated DCDM unit and can be installed in one base plate. In the DCDM unit, the DS can directly provide the influence functions and surface shape of the DM to the industrial computer in any adaptive optics system. As an integrated adaptive unit, the DCDM unit could be put into various optical systems to realize aberration compensation. In this paper, the configuration and principle of the DCDM unit is introduced first. Theoretical simulation on the close-loop performance of the DCDM unit is carried out. Finally, a verification experiment is proposed to verify the compensation capability of the DCDM unit.

Direct phase measurement in zonal wavefront reconstruction using multidither coherent optical adaptive technique.

PubMed

Liu, Rui; Milkie, Daniel E; Kerlin, Aaron; MacLennan, Bryan; Ji, Na

2014-01-27

In traditional zonal wavefront sensing for adaptive optics, after local wavefront gradients are obtained, the entire wavefront can be calculated by assuming that the wavefront is a continuous surface. Such an approach will lead to sub-optimal performance in reconstructing wavefronts which are either discontinuous or undersampled by the zonal wavefront sensor. Here, we report a new method to reconstruct the wavefront by directly measuring local wavefront phases in parallel using multidither coherent optical adaptive technique. This method determines the relative phases of each pupil segment independently, and thus produces an accurate wavefront for even discontinuous wavefronts. We implemented this method in an adaptive optical two-photon fluorescence microscopy and demonstrated its superior performance in correcting large or discontinuous aberrations.

Status of the DKIST system for solar adaptive optics

NASA Astrophysics Data System (ADS)

Johnson, Luke C.; Cummings, Keith; Drobilek, Mark; Johansson, Erik; Marino, Jose; Richards, Kit; Rimmele, Thomas; Sekulic, Predrag; Wöger, Friedrich

2016-07-01

When the Daniel K. Inouye Solar Telescope (DKIST) achieves first light in 2019, it will deliver the highest spatial resolution images of the solar atmosphere ever recorded. Additionally, the DKIST will observe the Sun with unprecedented polarimetric sensitivity and spectral resolution, spurring a leap forward in our understanding of the physical processes occurring on the Sun. The DKIST wavefront correction system will provide active alignment control and jitter compensation for all six of the DKIST science instruments. Five of the instruments will also be fed by a conventional adaptive optics (AO) system, which corrects for high frequency jitter and atmospheric wavefront disturbances. The AO system is built around an extended-source correlating Shack-Hartmann wavefront sensor, a Physik Instrumente fast tip-tilt mirror (FTTM) and a Xinetics 1600-actuator deformable mirror (DM), which are controlled by an FPGA-based real-time system running at 1975 Hz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r0 = 20 cm). The DKIST wavefront correction team has completed the design phase and is well into the fabrication phase. The FTTM and DM have both been delivered to the DKIST laboratory in Boulder, CO. The real-time controller has been completed and is able to read out the camera and deliver commands to the DM with a total latency of approximately 750 μs. All optics and optomechanics, including many high-precision custom optics, mounts, and stages, are completed or nearing the end of the fabrication process and will soon undergo rigorous acceptance testing. Before installing the wavefront correction system at the telescope, it will be assembled as a testbed in the laboratory. In the lab, performance tests beginning with component-level testing and continuing to full system testing will ensure that the wavefront correction system meets all performance requirements. Further work in the lab will focus on fine-tuning our alignment and calibration procedures so that installation and alignment on the summit will proceed as efficiently as possible.

Configuration optimization of laser guide stars and wavefront correctors for multi-conjugation adaptive optics

NASA Astrophysics Data System (ADS)

Xuan, Li; He, Bin; Hu, Li-Fa; Li, Da-Yu; Xu, Huan-Yu; Zhang, Xing-Yun; Wang, Shao-Xin; Wang, Yu-Kun; Yang, Cheng-Liang; Cao, Zhao-Liang; Mu, Quan-Quan; Lu, Xing-Hai

2016-09-01

Multi-conjugation adaptive optics (MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view (FOV). The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors, such as deformable mirrors (DMs) or liquid crystal wavefront correctors (LCWCs), is a very important step in the data processing of an MCAO’s controller. In this paper, a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars (LGSs) and the reasonable conjugation heights of LCWCs. Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO. Several examples are given to demonstrate our LGSs configuration optimization method. Compared with traditional methods, our method has minimum wavefront tomographic error, which will be helpful to get higher imaging resolution at large FOV in MCAO. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174274, 11174279, 61205021, 11204299, 61475152, and 61405194) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.

Grazing Incidence Wavefront Sensing and Verification of X-Ray Optics Performance

NASA Technical Reports Server (NTRS)

Saha, Timo T.; Rohrbach, Scott; Zhang, William W.

2011-01-01

Evaluation of interferometrically measured mirror metrology data and characterization of a telescope wavefront can be powerful tools in understanding of image characteristics of an x-ray optical system. In the development of soft x-ray telescope for the International X-Ray Observatory (IXO), we have developed new approaches to support the telescope development process. Interferometrically measuring the optical components over all relevant spatial frequencies can be used to evaluate and predict the performance of an x-ray telescope. Typically, the mirrors are measured using a mount that minimizes the mount and gravity induced errors. In the assembly and mounting process the shape of the mirror segments can dramatically change. We have developed wavefront sensing techniques suitable for the x-ray optical components to aid us in the characterization and evaluation of these changes. Hartmann sensing of a telescope and its components is a simple method that can be used to evaluate low order mirror surface errors and alignment errors. Phase retrieval techniques can also be used to assess and estimate the low order axial errors of the primary and secondary mirror segments. In this paper we describe the mathematical foundation of our Hartmann and phase retrieval sensing techniques. We show how these techniques can be used in the evaluation and performance prediction process of x-ray telescopes.

Analysis technique for controlling system wavefront error with active/adaptive optics

NASA Astrophysics Data System (ADS)

Genberg, Victor L.; Michels, Gregory J.

2017-08-01

The ultimate goal of an active mirror system is to control system level wavefront error (WFE). In the past, the use of this technique was limited by the difficulty of obtaining a linear optics model. In this paper, an automated method for controlling system level WFE using a linear optics model is presented. An error estimate is included in the analysis output for both surface error disturbance fitting and actuator influence function fitting. To control adaptive optics, the technique has been extended to write system WFE in state space matrix form. The technique is demonstrated by example with SigFit, a commercially available tool integrating mechanical analysis with optical analysis.

Polarization-Independent Silicon Metadevices for Efficient Optical Wavefront Control.

PubMed

Chong, Katie E; Staude, Isabelle; James, Anthony; Dominguez, Jason; Liu, Sheng; Campione, Salvatore; Subramania, Ganapathi S; Luk, Ting S; Decker, Manuel; Neshev, Dragomir N; Brener, Igal; Kivshar, Yuri S

2015-08-12

We experimentally demonstrate a functional silicon metadevice at telecom wavelengths that can efficiently control the wavefront of optical beams by imprinting a spatially varying transmittance phase independent of the polarization of the incident beam. Near-unity transmittance efficiency and close to 0-2π phase coverage are enabled by utilizing the localized electric and magnetic Mie-type resonances of low-loss silicon nanoparticles tailored to behave as electromagnetically dual-symmetric scatterers. We apply this concept to realize a metadevice that converts a Gaussian beam into a vortex beam. The required spatial distribution of transmittance phases is achieved by a variation of the lattice spacing as a single geometric control parameter.

The Durham Adaptive Optics Simulation Platform (DASP): Current status

NASA Astrophysics Data System (ADS)

Basden, A. G.; Bharmal, N. A.; Jenkins, D.; Morris, T. J.; Osborn, J.; Peng, J.; Staykov, L.

2018-01-01

The Durham Adaptive Optics Simulation Platform (DASP) is a Monte-Carlo modelling tool used for the simulation of astronomical and solar adaptive optics systems. In recent years, this tool has been used to predict the expected performance of the forthcoming extremely large telescope adaptive optics systems, and has seen the addition of several modules with new features, including Fresnel optics propagation and extended object wavefront sensing. Here, we provide an overview of the features of DASP and the situations in which it can be used. Additionally, the user tools for configuration and control are described.

ACCESS - A Science and Engineering Assessment of Space Coronagraph Concepts for the Direct Imaging and Spectroscopy of Exoplanetary Systems

NASA Technical Reports Server (NTRS)

Trauger, John

2008-01-01

Topics include and overview, science objectives, study objectives, coronagraph types, metrics, ACCESS observatory, laboratory validations, and summary. Individual slides examine ACCESS engineering approach, ACCESS gamut of coronagraph types, coronagraph metrics, ACCESS Discovery Space, coronagraph optical layout, wavefront control on the "level playing field", deformable mirror development for HCIT, laboratory testbed demonstrations, high contract imaging with the HCIT, laboratory coronagraph contrast and stability, model validation and performance predictions, HCIT coronagraph optical layout, Lyot coronagraph on the HCIT, pupil mapping (PIAA), shaped pupils, and vortex phase mask experiments on the HCIT.

Wavefront coherence area for predicting visual acuity of post-PRK and post-PARK refractive surgery patients

NASA Astrophysics Data System (ADS)

Garcia, Daniel D.; van de Pol, Corina; Barsky, Brian A.; Klein, Stanley A.

1999-06-01

Many current corneal topography instruments (called videokeratographs) provide an `acuity index' based on corneal smoothness to analyze expected visual acuity. However, post-refractive surgery patients often exhibit better acuity than is predicted by such indices. One reason for this is that visual acuity may not necessarily be determined by overall corneal smoothness but rather by having some part of the cornea able to focus light coherently onto the fovea. We present a new method of representing visual acuity by measuring the wavefront aberration, using principles from both ray and wave optics. For each point P on the cornea, we measure the size of the associated coherence area whose optical path length (OPL), from a reference plane to P's focus, is within a certain tolerance of the OPL for P. We measured the topographies and vision of 62 eyes of patients who had undergone the corneal refractive surgery procedures of photorefractive keratectomy (PRK) and photorefractive astigmatic keratectomy (PARK). In addition to high contrast visual acuity, our vision tests included low contrast and low luminance to test the contribution of the PRK transition zone. We found our metric for visual acuity to be better than all other metrics at predicting the acuity of low contrast and low luminance. However, high contrast visual acuity was poorly predicted by all of the indices we studied, including our own. The indices provided by current videokeratographs sometimes fail for corneas whose shape differs from simple ellipsoidal models. This is the case with post-PRK and post-PARK refractive surgery patients. Our alternative representation that displays the coherence area of the wavefront has considerable advantages, and promises to be a better predictor of low contrast and low luminance visual acuity than current shape measures.

Preliminary Investigation of an Active PLZT Lens

NASA Technical Reports Server (NTRS)

Lightsey, W. D.; Peters, B. R.; Reardon, P. J.; Wong, J. K.

2001-01-01

The design, analysis and preliminary testing of a prototype Adjustable Focus Optical Correction Lens (AFOCL) is described. The AFOCL is an active optical component composed of solid state lead lanthanum-modified zirconate titanate (PLZT) ferroelectric ceramic with patterned indium tin oxide (ITO) transparent surface electrodes that modulate the refractive index of the PLZT to function as an electro-optic lens. The AFOCL was developed to perform optical re-alignment and wavefront correction to enhance the performance of Ultra-Lightweight Structures and Space Observatories (ULSSO). The AFOCL has potential application as an active optical component within a larger optical system. As such, information from a wavefront sensor would be processed to provide input to the AFOCL to drive the sensed wavefront to the desired shape and location. While offering variable and rapid focussing capability (controlled wavefront manipulation) similar to liquid crystal based spatial light modulators (SLM), the AFOCL offers some potential advantages because it is a solid-state, stationary, low-mass, rugged, and thin optical element that can produce wavefront quality comparable to the solid refractive lens it replaces. The AFOCL acts as a positive or negative lens by producing a parabolic phase-shift in the PLZT material through the application of a controlled voltage potential across the ITO electrodes. To demonstrate the technology, a 4 mm diameter lens was fabricated to produce 5-waves of optical power operating at 2.051 micrometer wavelength. Optical metrology was performed on the device to measure focal length, optical quality, and efficiency for a variety of test configurations. The data was analyzed and compared to theoretical data available from computer-based models of the AFOCL.

FPGA-accelerated adaptive optics wavefront control

NASA Astrophysics Data System (ADS)

Mauch, S.; Reger, J.; Reinlein, C.; Appelfelder, M.; Goy, M.; Beckert, E.; Tünnermann, A.

2014-03-01

The speed of real-time adaptive optical systems is primarily restricted by the data processing hardware and computational aspects. Furthermore, the application of mirror layouts with increasing numbers of actuators reduces the bandwidth (speed) of the system and, thus, the number of applicable control algorithms. This burden turns out a key-impediment for deformable mirrors with continuous mirror surface and highly coupled actuator influence functions. In this regard, specialized hardware is necessary for high performance real-time control applications. Our approach to overcome this challenge is an adaptive optics system based on a Shack-Hartmann wavefront sensor (SHWFS) with a CameraLink interface. The data processing is based on a high performance Intel Core i7 Quadcore hard real-time Linux system. Employing a Xilinx Kintex-7 FPGA, an own developed PCie card is outlined in order to accelerate the analysis of a Shack-Hartmann Wavefront Sensor. A recently developed real-time capable spot detection algorithm evaluates the wavefront. The main features of the presented system are the reduction of latency and the acceleration of computation For example, matrix multiplications which in general are of complexity O(n3 are accelerated by using the DSP48 slices of the field-programmable gate array (FPGA) as well as a novel hardware implementation of the SHWFS algorithm. Further benefits are the Streaming SIMD Extensions (SSE) which intensively use the parallelization capability of the processor for further reducing the latency and increasing the bandwidth of the closed-loop. Due to this approach, up to 64 actuators of a deformable mirror can be handled and controlled without noticeable restriction from computational burdens.

Techniques for High-contrast Imaging in Multi-star Systems. II. Multi-star Wavefront Control

NASA Astrophysics Data System (ADS)

Sirbu, D.; Thomas, S.; Belikov, R.; Bendek, E.

2017-11-01

Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments due to the diffraction and aberration leakage caused by companion stars. Consequently, many scientifically valuable multi-star systems are excluded from direct imaging target lists for exoplanet surveys and characterization missions. Multi-star Wavefront Control (MSWC) is a technique that uses a coronagraphic instrument’s deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. MSWC uses “non-redundant” modes on the DM to independently control speckles from each star in the dark zone. Our previous paper also introduced the Super-Nyquist wavefront control technique, which uses a diffraction grating to generate high-contrast regions beyond the Nyquist limit (nominal region correctable by the DM). These two techniques can be combined as MSWC-s to generate high-contrast regions for multi-star systems at wide (Super-Nyquist) angular separations, while MSWC-0 refers to close (Sub-Nyquist) angular separations. As a case study, a high-contrast wavefront control simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged with a small aperture at 8× {10}-9 mean raw contrast in 10% broadband light in one-sided dark holes from 1.6-5.5 λ/D. Another case study using a larger 2.4 m aperture telescope such as the Wide-Field Infrared Survey Telescope uses these techniques to image the habitable zone of Alpha Centauri at 3.2× {10}-9 mean raw contrast in monochromatic light.

Ocular wavefront analysis of aspheric compared with spherical monofocal intraocular lenses in cataract surgery: Systematic review with metaanalysis.

PubMed

Schuster, Alexander K; Tesarz, Jonas; Vossmerbaeumer, Urs

2015-05-01

This review was conducted to compare the physical effect of aspheric IOL implantation on wavefront properties with that of spherical IOL implantation. The peer-reviewed literature was systematically searched in Medline, Embase, Web of Science, Biosis, and the Cochrane Library according to the Cochrane Collaboration method. Inclusion criteria were randomized controlled trials comparing the use of aspheric versus spherical monofocal IOL implantation that assessed visual acuity, contrast sensitivity, or quality of vision. A secondary outcome was ocular wavefront analysis; spherical aberration, higher-order aberrations (HOAs), coma, and trefoil were evaluated. Effects were calculated as standardized mean differences (Hedges g) and were pooled using random-effect models. Thirty-four of 43 studies provided data for wavefront analysis. Aspheric monofocal IOL implantation resulted in less ocular spherical aberration and fewer ocular HOAs than spherical IOLs. This might explain the better contrast sensitivity in patients with aspheric IOLs. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Comparison of different 3D wavefront sensing and reconstruction techniques for MCAO

NASA Astrophysics Data System (ADS)

Bello, Dolores; Vérinaud, Christophe; Conan, Jean-Marc; Fusco, Thierry; Carbillet, Marcel; Esposito, Simone

2003-02-01

The vertical distribution of the turbulence limits the field of view of classical adaptive optics due to the anisoplanatism. Multiconjugate adaptive optics (MCAO) uses several deformable mirrors conjugated to different layers in the atmosphere to overcome this effect. In the last few years, many studies and developments have been done regarding the analysis of the turbulence volume, and the choice of the wavefront reconstruction techniques.An extensive study of MCAO modelisation and performance estimation has been done at OAA and ONERA. The developed Monte Carlo codes allow to simulate and investigate many aspects: comparison of turbulence analysis strategies (tomography or layer oriented) and comparison of different reconstruction approaches. For instance in the layer oriented approach, the control for a given deformable mirror can be either deduced from the whole set of wavefront sensor measurements or only using the associated wavefront sensor. Numerical simulations are presented showing the advantages and disadvantages of these different options for several cases depending on the number, geometry and magnitude of the guide stars.

Coherent control of plasma dynamics

NASA Astrophysics Data System (ADS)

He, Zhaohan

2014-10-01

The concept of coherent control - precise measurement or determination of a process through control of the phase of an applied oscillating field - has been applied to numerous systems with great success. Here, we demonstrate the use of coherent control on plasma dynamics in a laser wakefield electron acceleration experiment. A tightly focused femtosecond laser pulse (10 mJ, 35 fs) was used to generate electron beams by plasma wakefield acceleration in the density down ramp. The technique is based on optimization of the electron beam using a deformable mirror adaptive optical system with an iterative evolutionary genetic algorithm. The image of the electrons on a scintillator screen was processed and used in a fitness function as direct feedback for the optimization algorithm. This coherent manipulation of the laser wavefront leads to orders of magnitude improvement to the electron beam properties such as the peak charge and beam divergence. The laser beam optimized to generate the best electron beam was not the one with the ``best'' focal spot. When a particular wavefront of laser light interacts with plasma, it can affect the plasma wave structures and trapping conditions of the electrons in a complex way. For example, Raman forward scattering, envelope self-modulation, relativistic self-focusing, and relativistic self-phase modulation and many other nonlinear interactions modify both the pulse envelope and phase as the pulse propagates, in a way that cannot be easily predicted and that subsequently dictates the formation of plasma waves. The optimal wavefront could be successfully determined via the heuristic search under laser-plasma conditions that were not known a priori. Control and shaping of the electron energy distribution was found to be less effective, but was still possible. Particle-in-cell simulations were performed to show that the mode structure of the laser beam can affect the plasma wave structure and trapping conditions of electrons, which subsequently produces electron beams with a different divergence. The proof-of-principle demonstration of coherent control for plasmas opens new possibilities for future laser-based accelerators and their applications. This study should also enable a significantly improved understanding of the complex dynamics of laser plasma interactions. This work was supported by DARPA under Contract No. N66001-11-1-4208, the NSF under Contract No. 0935197 and MCubed at the University of Michigan.

Comparison of wavefront sensor models for simulation of adaptive optics.

PubMed

Wu, Zhiwen; Enmark, Anita; Owner-Petersen, Mette; Andersen, Torben

2009-10-26

The new generation of extremely large telescopes will have adaptive optics. Due to the complexity and cost of such systems, it is important to simulate their performance before construction. Most systems planned will have Shack-Hartmann wavefront sensors. Different mathematical models are available for simulation of such wavefront sensors. The choice of wavefront sensor model strongly influences computation time and simulation accuracy. We have studied the influence of three wavefront sensor models on performance calculations for a generic, adaptive optics (AO) system designed for K-band operation of a 42 m telescope. The performance of this AO system has been investigated both for reduced wavelengths and for reduced r(0) in the K band. The telescope AO system was designed for K-band operation, that is both the subaperture size and the actuator pitch were matched to a fixed value of r(0) in the K-band. We find that under certain conditions, such as investigating limiting guide star magnitude for large Strehl-ratios, a full model based on Fraunhofer propagation to the subimages is significantly more accurate. It does however require long computation times. The shortcomings of simpler models based on either direct use of average wavefront tilt over the subapertures for actuator control, or use of the average tilt to move a precalculated point spread function in the subimages are most pronounced for studies of system limitations to operating parameter variations. In the long run, efficient parallelization techniques may be developed to overcome the problem.

The Physics of Boundary-Layer Aero-Optic Effects

DTIC Science & Technology

2012-09-01

various models to predict aero-optical effects for both subsonic and supersonic Mach numbers, laser beam sizes and non- adiabatic walls. The developed...models to predict aero-optical effects for both subsonic and supersonic Mach numbers, laser beam sizes and non- adiabatic walls. The developed models were... Supersonic Facilities .................................................................................................... 8 3.3 2-D Wavefront Data

Wavefront sensorless adaptive optics optical coherence tomography for in vivo retinal imaging in mice

PubMed Central

Jian, Yifan; Xu, Jing; Gradowski, Martin A.; Bonora, Stefano; Zawadzki, Robert J.; Sarunic, Marinko V.

2014-01-01

We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging. WSAO is attractive especially for mouse retinal imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data, acquired in vivo. PMID:24575347

Adaptive optics for array telescopes using piston-and-tilt wave-front sensing

NASA Technical Reports Server (NTRS)

Wizinowich, P.; Mcleod, B.; Lloyd-Yhart, M.; Angel, J. R. P.; Colucci, D.; Dekany, R.; Mccarthy, D.; Wittman, D.; Scott-Fleming, I.

1992-01-01

A near-infrared adaptive optics system operating at about 50 Hz has been used to control phase errors adaptively between two mirrors of the Multiple Mirror Telescope by stabilizing the position of the interference fringe in the combined unresolved far-field image. The resultant integrated images have angular resolutions of better than 0.1 arcsec and fringe contrasts of more than 0.6. Measurements of wave-front tilt have confirmed the wavelength independence of image motion. These results show that interferometric sensing of phase errors, when combined with a system for sensing the wave-front tilt of the individual telescopes, will provide a means of achieving a stable diffraction-limited focus with segmented telescopes or arrays of telescopes.

Numerical analysis of wavefront measurement characteristics by using plenoptic camera

NASA Astrophysics Data System (ADS)

Lv, Yang; Ma, Haotong; Zhang, Xuanzhe; Ning, Yu; Xu, Xiaojun

2016-01-01

To take advantage of the large-diameter telescope for high-resolution imaging of extended targets, it is necessary to detect and compensate the wave-front aberrations induced by atmospheric turbulence. Data recorded by Plenoptic cameras can be used to extract the wave-front phases associated to the atmospheric turbulence in an astronomical observation. In order to recover the wave-front phase tomographically, a method of completing the large Field Of View (FOV), multi-perspective wave-front detection simultaneously is urgently demanded, and it is plenoptic camera that possesses this unique advantage. Our paper focuses more on the capability of plenoptic camera to extract the wave-front from different perspectives simultaneously. In this paper, we built up the corresponding theoretical model and simulation system to discuss wave-front measurement characteristics utilizing plenoptic camera as wave-front sensor. And we evaluated the performance of plenoptic camera with different types of wave-front aberration corresponding to the occasions of applications. In the last, we performed the multi-perspective wave-front sensing employing plenoptic camera as wave-front sensor in the simulation. Our research of wave-front measurement characteristics employing plenoptic camera is helpful to select and design the parameters of a plenoptic camera, when utilizing which as multi-perspective and large FOV wave-front sensor, which is expected to solve the problem of large FOV wave-front detection, and can be used for AO in giant telescopes.

MOEMs devices designed and tested for future astronomical instrumentation in space

NASA Astrophysics Data System (ADS)

Zamkotsian, Frédéric; Lanzoni, Patrick; Waldis, Severin; Noell, Wilfried; Conedera, Veronique; Fabre, Norbert; Viard, Thierry; Buisset, Christophe

2017-11-01

Next generation of astronomical instrumentation for space telescopes requires Micro-Opto-Electro- Mechanical Systems (MOEMS) with remote control capability and cryogenic operation. MOEMS devices have the capability to tailor the incoming light in terms of intensity and object selection with programmable slit masks, in terms of phase and wavefront control with micro-deformable mirrors, and finally in terms of spectrum with programmable diffraction gratings. Applications are multi-object spectroscopy (MOS), wavefront correction and programmable spectrographs. We are engaged since several years in the design, realization and characterization of MOEMS devices suited for astronomical instrumentation.

Implementing transmission eigenchannels of disordered media by a binary-control digital micromirror device

NASA Astrophysics Data System (ADS)

Kim, Donggyu; Choi, Wonjun; Kim, Moonseok; Moon, Jungho; Seo, Keumyoung; Ju, Sanghyun; Choi, Wonshik

2014-11-01

We report a method for measuring the transmission matrix of a disordered medium using a binary-control of a digital micromirror device (DMD). With knowledge of the measured transmission matrix, we identified the transmission eigenchannels of the medium. We then used binary control of the DMD to shape the wavefront of incident waves and to experimentally couple light to individual eigenchannels. When the wave was coupled to the eigenchannel with the largest eigenvalue, in particular, we were able to achieve about two times more energy transmission than the mean transmittance of the medium. Our study provides an elaborated use of the DMD as a high-speed wavefront shaping device for controlling the multiple scattering of waves in highly scattering media.

Analysis of wave propagation and wavefront sensing in target-in-the-loop beam control systems

NASA Astrophysics Data System (ADS)

Vorontsov, Mikhail A.; Kolosov, Valeri V.

2004-10-01

Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related with maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing outgoing wave propagation, and the equation describing evolution of the mutual intensity function (MIF) for the backscattered (returned) wave. The resulting evolution equation for the MIF is further simplified by the use of the smooth refractive index approximation. This approximation enables derivation of the transport equation for the returned wave brightness function, analyzed here using method characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wavefront sensors that perform sensing of speckle-averaged characteristics of the wavefront phase (TIL sensors). Analysis of the wavefront phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric turbulence-related phase aberrations. We also show that wavefront sensing results depend on the extended target shape, surface roughness, and the outgoing beam intensity distribution on the target surface.

Comparative analysis of methods and optical-electronic equipment to control the form parameters of spherical mirrors

NASA Astrophysics Data System (ADS)

Nikitin, Alexander N.; Baryshnikov, Nikolay; Denisov, Dmitrii; Karasik, Valerii; Sakharov, Alexey; Romanov, Pavel; Sheldakova, Julia; Kudryashov, Alexis

2018-02-01

In this paper we consider two approaches widely used in testing of spherical optical surfaces: Fizeau interferometer and Shack-Hartmann wavefront sensor. Fizeau interferometer that is widely used in optical testing can be transformed to a device using Shack-Hartmann wavefront sensor, the alternative technique to check spherical optical components. We call this device Hartmannometer, and compare its features to those of Fizeau interferometer.

Hybrid architecture active wavefront sensing and control system, and method

NASA Technical Reports Server (NTRS)

Feinberg, Lee D. (Inventor); Dean, Bruce H. (Inventor); Hyde, Tristram T. (Inventor)

2011-01-01

According to various embodiments, provided herein is an optical system and method that can be configured to perform image analysis. The optical system can comprise a telescope assembly and one or more hybrid instruments. The one or more hybrid instruments can be configured to receive image data from the telescope assembly and perform a fine guidance operation and a wavefront sensing operation, simultaneously, on the image data received from the telescope assembly.

Large-field-of-view imaging by multi-pupil adaptive optics.

PubMed

Park, Jung-Hoon; Kong, Lingjie; Zhou, Yifeng; Cui, Meng

2017-06-01

Adaptive optics can correct for optical aberrations. We developed multi-pupil adaptive optics (MPAO), which enables simultaneous wavefront correction over a field of view of 450 × 450 μm 2 and expands the correction area to nine times that of conventional methods. MPAO's ability to perform spatially independent wavefront control further enables 3D nonplanar imaging. We applied MPAO to in vivo structural and functional imaging in the mouse brain.

Model-based wavefront sensorless adaptive optics system for large aberrations and extended objects.

PubMed

Yang, Huizhen; Soloviev, Oleg; Verhaegen, Michel

2015-09-21

A model-based wavefront sensorless (WFSless) adaptive optics (AO) system with a 61-element deformable mirror is simulated to correct the imaging of a turbulence-degraded extended object. A fast closed-loop control algorithm, which is based on the linear relation between the mean square of the aberration gradients and the second moment of the image intensity distribution, is used to generate the control signals for the actuators of the deformable mirror (DM). The restoration capability and the convergence rate of the AO system are investigated with different turbulence strength wave-front aberrations. Simulation results show the model-based WFSless AO system can restore those images degraded by different turbulence strengths successfully and obtain the correction very close to the achievable capability of the given DM. Compared with the ideal correction of 61-element DM, the averaged relative error of RMS value is 6%. The convergence rate of AO system is independent of the turbulence strength and only depends on the number of actuators of DM.

Recent developments for the Large Binocular Telescope Guiding Control Subsystem

NASA Astrophysics Data System (ADS)

Golota, T.; De La Peña, M. D.; Biddick, C.; Lesser, M.; Leibold, T.; Miller, D.; Meeks, R.; Hahn, T.; Storm, J.; Sargent, T.; Summers, D.; Hill, J.; Kraus, J.; Hooper, S.; Fisher, D.

2014-07-01

The Large Binocular Telescope (LBT) has eight Acquisition, Guiding, and wavefront Sensing Units (AGw units). They provide guiding and wavefront sensing capability at eight different locations at both direct and bent Gregorian focal stations. Recent additions of focal stations for PEPSI and MODS instruments doubled the number of focal stations in use including respective motion, camera controller server computers, and software infrastructure communicating with Guiding Control Subsystem (GCS). This paper describes the improvements made to the LBT GCS and explains how these changes have led to better maintainability and contributed to increased reliability. This paper also discusses the current GCS status and reviews potential upgrades to further improve its performance.

Acoustic imaging microscope

DOEpatents

Deason, Vance A.; Telschow, Kenneth L.

2006-10-17

An imaging system includes: an object wavefront source and an optical microscope objective all positioned to direct an object wavefront onto an area of a vibrating subject surface encompassed by a field of view of the microscope objective, and to direct a modulated object wavefront reflected from the encompassed surface area through a photorefractive material; and a reference wavefront source and at least one phase modulator all positioned to direct a reference wavefront through the phase modulator and to direct a modulated reference wavefront from the phase modulator through the photorefractive material to interfere with the modulated object wavefront. The photorefractive material has a composition and a position such that interference of the modulated object wavefront and modulated reference wavefront occurs within the photorefractive material, providing a full-field, real-time image signal of the encompassed surface area.

High precision wavefront control in point spread function engineering for single emitter localization

NASA Astrophysics Data System (ADS)

Siemons, M.; Hulleman, C. N.; Thorsen, R. Ø.; Smith, C. S.; Stallinga, S.

2018-04-01

Point Spread Function (PSF) engineering is used in single emitter localization to measure the emitter position in 3D and possibly other parameters such as the emission color or dipole orientation as well. Advanced PSF models such as spline fits to experimental PSFs or the vectorial PSF model can be used in the corresponding localization algorithms in order to model the intricate spot shape and deformations correctly. The complexity of the optical architecture and fit model makes PSF engineering approaches particularly sensitive to optical aberrations. Here, we present a calibration and alignment protocol for fluorescence microscopes equipped with a spatial light modulator (SLM) with the goal of establishing a wavefront error well below the diffraction limit for optimum application of complex engineered PSFs. We achieve high-precision wavefront control, to a level below 20 m$\\lambda$ wavefront aberration over a 30 minute time window after the calibration procedure, using a separate light path for calibrating the pixel-to-pixel variations of the SLM, and alignment of the SLM with respect to the optical axis and Fourier plane within 3 $\\mu$m ($x/y$) and 100 $\\mu$m ($z$) error. Aberrations are retrieved from a fit of the vectorial PSF model to a bead $z$-stack and compensated with a residual wavefront error comparable to the error of the SLM calibration step. This well-calibrated and corrected setup makes it possible to create complex `3D+$\\lambda$' PSFs that fit very well to the vectorial PSF model. Proof-of-principle bead experiments show precisions below 10~nm in $x$, $y$, and $\\lambda$, and below 20~nm in $z$ over an axial range of 1 $\\mu$m with 2000 signal photons and 12 background photons.

Control of her1 expression during zebrafish somitogenesis by a Delta-dependent oscillator and an independent wave-front activity

PubMed Central

Holley, Scott A.; Geisler, Robert; Nüsslein-Volhard, Christiane

2000-01-01

Somitogenesis has been linked both to a molecular clock that controls the oscillation of gene expression in the presomitic mesoderm (PSM) and to Notch pathway signaling. The oscillator, or clock, is thought to create a prepattern of stripes of gene expression that regulates the activity of the Notch pathway that subsequently directs somite border formation. Here, we report that the zebrafish gene after eight (aei) that is required for both somitogenesis and neurogenesis encodes the Notch ligand DeltaD. Additional analysis revealed that stripes of her1 expression oscillate within the PSM and that aei/DeltaD signaling is required for this oscillation. aei/DeltaD expression does not oscillate, indicating that the activity of the Notch pathway upstream of her1 may function within the oscillator itself. Moreover, we found that her1 stripes are expressed in the anlage of consecutive somites, indicating that its expression pattern is not pair-rule. Analysis of her1 expression in aei/DeltaD, fused somites (fss), and aei;fss embryos uncovered a wave-front activity that is capable of continually inducing her1 expression de novo in the anterior PSM in the absence of the oscillation of her1. The wave-front activity, in reference to the clock and wave-front model, is defined as such because it interacts with the oscillator-derived pattern in the anterior PSM and is required for somite morphogenesis. This wave-front activity is blocked in embryos mutant for fss but not aei/DeltaD. Thus, our analysis indicates that the smooth sequence of formation, refinement, and fading of her1 stripes in the PSM is governed by two separate activities. PMID:10887161

ATLAST ULE mirror segment performance analytical predictions based on thermally induced distortions

NASA Astrophysics Data System (ADS)

Eisenhower, Michael J.; Cohen, Lester M.; Feinberg, Lee D.; Matthews, Gary W.; Nissen, Joel A.; Park, Sang C.; Peabody, Hume L.

2015-09-01

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for a 9.2 m aperture space-borne observatory operating across the UV/Optical/NIR spectra. The primary mirror for ATLAST is a segmented architecture with pico-meter class wavefront stability. Due to its extraordinarily low coefficient of thermal expansion, a leading candidate for the primary mirror substrate is Corning's ULE® titania-silicate glass. The ATLAST ULE® mirror substrates will be maintained at `room temperature' during on orbit flight operations minimizing the need for compensation of mirror deformation between the manufacturing temperature and the operational temperatures. This approach requires active thermal management to maintain operational temperature while on orbit. Furthermore, the active thermal control must be sufficiently stable to prevent time-varying thermally induced distortions in the mirror substrates. This paper describes a conceptual thermal management system for the ATLAST 9.2 m segmented mirror architecture that maintains the wavefront stability to less than 10 pico-meters/10 minutes RMS. Thermal and finite element models, analytical techniques, accuracies involved in solving the mirror figure errors, and early findings from the thermal and thermal-distortion analyses are presented.

A new wavefront sensor with polar symmetry: quantitative comparisons with a Shack-Hartmann wavefront sensor.

PubMed

Carvalho, Luis Alberto; Castro, Jarbas; Chamon, Wallace; Schor, Paulo

2006-11-01

A novel wavefront sensor has been developed. It follows the same principle of the Shack-Hartmann wavefront sensor in that it is based on slope information. However, it has a different symmetry, which may offer benefits in terms of application. The new wavefront sensor consists of a set of donut-shaped acrylic lenses with a charge coupled device located at the focal plane. From detection of shift in the radial direction, radial slopes are computed for 2880 points. Theoretical computations for higher order aberrations and lower order aberrations were implemented for the Shack-Hartmann wavefront sensor and the new wavefront sensor, and practical measurements were conducted on several sphere-cylinder trial lenses. The overall mean value of root mean square error (RMSE) (in microns) for theoretical computations was 0.03 for the Shack-Hartmann wavefront sensor and 0.02 for the new wavefront sensor. The mean value of RMSE for lower order aberrations (1-5) was 0.01 and 0.00003, and for higher order aberrations was 0.02 and 0.02, for the Shack-Hartmann and new wavefront sensors, respectively. For practical measurements (sphere, cylinder, axis), the standard deviation was 0.04 diopters (D), 0.04 D, and 4 degrees for the new wavefront sensor and 0.02 D, 0.02 D, and 5 degrees for the Shack-Hartmann wavefront sensor. Precision of the new wavefront sensor when measuring astigmatic and spherical surfaces is compatible with the Shack-Hartmann wavefront sensor. Centration with this new sensor is an absolute process using the center of the entrance pupil, which is where the line of site passes. This wavefront sensor, similar to the Shack-Hartmann sensor, does not eliminate the possibility of tilt. For more conclusive and statistically valid data, in vivo measurements are needed.

Wavefront-guided versus wavefront-optimized laser in situ keratomileusis: contralateral comparative study.

PubMed

Padmanabhan, Prema; Mrochen, Michael; Basuthkar, Subam; Viswanathan, Deepa; Joseph, Roy

2008-03-01

To compare the outcomes of wavefront-guided and wavefront-optimized treatment in fellow eyes of patients having laser in situ keratomileusis (LASIK) for myopia. Medical and Vision Research Foundation, Tamil Nadu, India. This prospective comparative study comprised 27 patients who had wavefront-guided LASIK in 1 eye and wavefront-optimized LASIK in the fellow eye. The Hansatome (Bausch & Lomb) was used to create a superior-hinged flap and the Allegretto laser (WaveLight Laser Technologie AG), for photoablation. The Allegretto wave analyzer was used to measure ocular wavefront aberrations and the Functional Acuity Contrast Test chart, to measure contrast sensitivity before and 1 month after LASIK. The refractive and visual outcomes and the changes in aberrations and contrast sensitivity were compared between the 2 treatment modalities. One month postoperatively, 92% of eyes in the wavefront-guided group and 85% in the wavefront-optimized group had uncorrected visual acuity of 20/20 or better; 93% and 89%, respectively, had a postoperative spherical equivalent refraction of +/-0.50 diopter. The differences between groups were not statistically significant. Wavefront-guided LASIK induced less change in 18 of 22 higher-order Zernike terms than wavefront-optimized LASIK, with the change in positive spherical aberration the only statistically significant one (P= .01). Contrast sensitivity improved at the low and middle spatial frequencies (not statistically significant) and worsened significantly at high spatial frequencies after wavefront-guided LASIK; there was a statistically significant worsening at all spatial frequencies after wavefront-optimized LASIK. Although both wavefront-guided and wavefront-optimized LASIK gave excellent refractive correction results, the former induced less higher-order aberrations and was associated with better contrast sensitivity.

Design and implementation of a scene-dependent dynamically selfadaptable wavefront coding imaging system

NASA Astrophysics Data System (ADS)

Carles, Guillem; Ferran, Carme; Carnicer, Artur; Bosch, Salvador

2012-01-01

A computational imaging system based on wavefront coding is presented. Wavefront coding provides an extension of the depth-of-field at the expense of a slight reduction of image quality. This trade-off results from the amount of coding used. By using spatial light modulators, a flexible coding is achieved which permits it to be increased or decreased as needed. In this paper a computational method is proposed for evaluating the output of a wavefront coding imaging system equipped with a spatial light modulator, with the aim of thus making it possible to implement the most suitable coding strength for a given scene. This is achieved in an unsupervised manner, thus the whole system acts as a dynamically selfadaptable imaging system. The program presented here controls the spatial light modulator and the camera, and also processes the images in a synchronised way in order to implement the dynamic system in real time. A prototype of the system was implemented in the laboratory and illustrative examples of the performance are reported in this paper. Program summaryProgram title: DynWFC (Dynamic WaveFront Coding) Catalogue identifier: AEKC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 10 483 No. of bytes in distributed program, including test data, etc.: 2 437 713 Distribution format: tar.gz Programming language: Labview 8.5 and NI Vision and MinGW C Compiler Computer: Tested on PC Intel ® Pentium ® Operating system: Tested on Windows XP Classification: 18 Nature of problem: The program implements an enhanced wavefront coding imaging system able to adapt the degree of coding to the requirements of a specific scene. The program controls the acquisition by a camera, the display of a spatial light modulator and the image processing operations synchronously. The spatial light modulator is used to implement the phase mask with flexibility given the trade-off between depth-of-field extension and image quality achieved. The action of the program is to evaluate the depth-of-field requirements of the specific scene and subsequently control the coding established by the spatial light modulator, in real time.

Ultra high frequency imaging acoustic microscope

DOEpatents

Deason, Vance A.; Telschow, Kenneth L.

2006-05-23

An imaging system includes: an object wavefront source and an optical microscope objective all positioned to direct an object wavefront onto an area of a vibrating subject surface encompassed by a field of view of the microscope objective, and to direct a modulated object wavefront reflected from the encompassed surface area through a photorefractive material; and a reference wavefront source and at least one phase modulator all positioned to direct a reference wavefront through the phase modulator and to direct a modulated reference wavefront from the phase modulator through the photorefractive material to interfere with the modulated object wavefront. The photorefractive material has a composition and a position such that interference of the modulated object wavefront and modulated reference wavefront occurs within the photorefractive material, providing a full-field, real-time image signal of the encompassed surface area.

Correction of the wavefront using the irradiance transport equation

NASA Astrophysics Data System (ADS)

García, M.; Granados, F.; Cornejo, A.

2008-07-01

The correction of the wavefront in optical systems implies the use of wavefront sensors, software, and auxiliary optical systems. We propose evaluated the wavefront using the fact that the wavefront and its intensity are related in the mathematical expression the irradiance transport equation (ITE)

Results from SIM's Thermo-Opto-Mechanical (TOM3) Testbed

NASA Technical Reports Server (NTRS)

Goullioud, Renaud; Lindensmith, C. A.; Hahn, I.

2006-01-01

Future space-based optical interferometers, such as the Space Interferometer Mission Planet Quest (SIM), require thermal stability of the optical wavefront to the level of picometers in order to produce astrometric data at the micro-arc-second level. In SIM, the internal path of the interferometer will be measured with a small metrology beam whereas the starlight fringe position is estimated from a large concentric annular beam. To achieve the micro-arc-second observation goal for SIM, it is necessary to maintain the optical path difference between the central and the outer annulus portions of the wavefront of the front-end telescope optics to a few tens of picometers. The Thermo-Opto-Mecha nical testbed (TOM3) was developed at the Jet Propulsion Laboratory to measure thermally induced optical deformations of a full-size flight-like beam compressor and siderostat, the two largest optics on SIM, in flight-like thermal environments. A Common Path Heterodyne Interferometer (COPHI) developed at JPL was used for the fine optical path difference measurement as the metrology sensor. The system was integrated inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. The siderostat was installed in a temperature-controlled thermal shroud inside the vacuum chamber, creating a flight-like thermal environment. Detailed thermal and structural models of the test articles (siderostat and compressor) were also developed for model prediction and correlation of the thermal deformations. Experimental data shows SIM required thermal stability of the test articles and good agreement with the model predictions.

Simpler Adaptive Optics using a Single Device for Processing and Control

NASA Astrophysics Data System (ADS)

Zovaro, A.; Bennet, F.; Rye, D.; D'Orgeville, C.; Rigaut, F.; Price, I.; Ritchie, I.; Smith, C.

The management of low Earth orbit is becoming more urgent as satellite and debris densities climb, in order to avoid a Kessler syndrome. A key part of this management is to precisely measure the orbit of both active satellites and debris. The Research School of Astronomy and Astrophysics at the Australian National University have been developing an adaptive optics (AO) system to image and range orbiting objects. The AO system provides atmospheric correction for imaging and laser ranging, allowing for the detection of smaller angular targets and drastically increasing the number of detectable objects. AO systems are by nature very complex and high cost systems, often costing millions of dollars and taking years to design. It is not unusual for AO systems to comprise multiple servers, digital signal processors (DSP) and field programmable gate arrays (FPGA), with dedicated tasks such as wavefront sensor data processing or wavefront reconstruction. While this multi-platform approach has been necessary in AO systems to date due to computation and latency requirements, this may no longer be the case for those with less demanding processing needs. In recent years, large strides have been made in FPGA and microcontroller technology, with todays devices having clock speeds in excess of 200 MHz whilst using a < 5 V power supply. AO systems using a single such device for all data processing and control may present a far simpler, cheaper, smaller and more efficient solution than existing systems. A novel AO system design based around a single, low-cost controller is presented. The objective is to determine the performance which can be achieved in terms of bandwidth and correction order, with a focus on optimisation and parallelisation of AO algorithms such as wavefront measurement and reconstruction. The AO system consists of a Shack-Hartmann wavefront sensor and a deformable mirror to correct light from a 1.8 m telescope for the purpose of imaging orbiting satellites. The microcontroller or FPGA interfaces directly with the wavefront sensor detector and deformable mirror. Wavefront slopes are calculated from each detector frame and converted into actuator commands to complete the closed loop AO control system. A particular challenge of this system is to optimise the AO algorithms to achieve a high rate (> 1kHz) with low latency (< 1ms) to achieve a good AO correction. As part of the Space Environment Cooperative Research Centre (SERC) this AO system design will be used as a demonstrator for what is possible with ground based AO corrected satellite imaging and ranging systems. The ability to directly and efficiently interface the wavefront sensor and deformable mirror is an important step in reducing the cost and complexity of an AO system. It is hoped that in the future this design can be modified for use in general AO applications, such as in 1-3 m telescopes for space surveillance, or even for amateur astronomy.

Shaping Microwave Fields Using Nonlinear Unsolicited Feedback: Application to Enhance Energy Harvesting

NASA Astrophysics Data System (ADS)

del Hougne, Philipp; Fink, Mathias; Lerosey, Geoffroy

2017-12-01

Wave-front shaping has emerged over the past decade as a powerful tool to control wave propagation through complex media, initially in optics and more recently also in the microwave domain with important applications in telecommunication, imaging, and energy transfer. The crux of implementing wave-front shaping concepts in real life is often its need for (direct) feedback, requiring access to the target to focus on. Here, we present the shaping of a microwave field based on indirect, unsolicited, and blind feedback which may be the pivotal step towards practical implementations. With the example of a radio-frequency harvester in a metallic cavity, we demonstrate tenfold enhancement of the harvested power by wave-front shaping based on nonlinear signals detected at an arbitrary position away from the harvesting device.

Shaped pupil coronagraphy for WFIRST: high-contrast broadband testbed demonstration

NASA Astrophysics Data System (ADS)

Cady, Eric; Balasubramanian, Kunjithapatham; Gersh-Range, Jessica; Kasdin, Jeremy; Kern, Brian; Lam, Raymond; Mejia Prada, Camilo; Moody, Dwight; Patterson, Keith; Poberezhskiy, Ilya; Riggs, A. J. Eldorado; Seo, Byoung-Joon; Shi, Fang; Tang, Hong; Trauger, John; Zhou, Hanying; Zimmerman, Neil

2017-09-01

The Shaped Pupil Coronagraph (SPC) is one of the two operating modes of the WFIRST coronagraph instrument. The SPC provides starlight suppression in a pair of wedge-shaped regions over an 18% bandpass, and is well suited for spectroscopy of known exoplanets. To demonstrate this starlight suppression in the presence of expected onorbit input wavefront disturbances, we have recently built a dynamic testbed at JPL analogous to the WFIRST flight instrument architecture, with both Hybrid Lyot Coronagraph (HLC) and SPC architectures and a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to apply, sense, and correct dynamic wavefront disturbances. We present our best up-to-date results of the SPC mode demonstration from the testbed, in both static and dynamic conditions, along with model comparisons. HLC results will be reported separately.

Layer-oriented multigrid wavefront reconstruction algorithms for multi-conjugate adaptive optics

NASA Astrophysics Data System (ADS)

Gilles, Luc; Ellerbroek, Brent L.; Vogel, Curtis R.

2003-02-01

Multi-conjugate adaptive optics (MCAO) systems with 104-105 degrees of freedom have been proposed for future giant telescopes. Using standard matrix methods to compute, optimize, and implement wavefront control algorithms for these systems is impractical, since the number of calculations required to compute and apply the reconstruction matrix scales respectively with the cube and the square of the number of AO degrees of freedom. In this paper, we develop an iterative sparse matrix implementation of minimum variance wavefront reconstruction for telescope diameters up to 32m with more than 104 actuators. The basic approach is the preconditioned conjugate gradient method, using a multigrid preconditioner incorporating a layer-oriented (block) symmetric Gauss-Seidel iterative smoothing operator. We present open-loop numerical simulation results to illustrate algorithm convergence.

Wavefront detection method of a single-sensor based adaptive optics system.

PubMed

Wang, Chongchong; Hu, Lifa; Xu, Huanyu; Wang, Yukun; Li, Dayu; Wang, Shaoxin; Mu, Quanquan; Yang, Chengliang; Cao, Zhaoliang; Lu, Xinghai; Xuan, Li

2015-08-10

In adaptive optics system (AOS) for optical telescopes, the reported wavefront sensing strategy consists of two parts: a specific sensor for tip-tilt (TT) detection and another wavefront sensor for other distortions detection. Thus, a part of incident light has to be used for TT detection, which decreases the light energy used by wavefront sensor and eventually reduces the precision of wavefront correction. In this paper, a single Shack-Hartmann wavefront sensor based wavefront measurement method is presented for both large amplitude TT and other distortions' measurement. Experiments were performed for testing the presented wavefront method and validating the wavefront detection and correction ability of the single-sensor based AOS. With adaptive correction, the root-mean-square of residual TT was less than 0.2 λ, and a clear image was obtained in the lab. Equipped on a 1.23-meter optical telescope, the binary stars with angle distance of 0.6″ were clearly resolved using the AOS. This wavefront measurement method removes the separate TT sensor, which not only simplifies the AOS but also saves light energy for subsequent wavefront sensing and imaging, and eventually improves the detection and imaging capability of the AOS.

Using integrated models to minimize environmentally induced wavefront error in optomechanical design and analysis

NASA Astrophysics Data System (ADS)

Genberg, Victor L.; Michels, Gregory J.

2017-08-01

The ultimate design goal of an optical system subjected to dynamic loads is to minimize system level wavefront error (WFE). In random response analysis, system WFE is difficult to predict from finite element results due to the loss of phase information. In the past, the use of ystem WFE was limited by the difficulty of obtaining a linear optics model. In this paper, an automated method for determining system level WFE using a linear optics model is presented. An error estimate is included in the analysis output based on fitting errors of mode shapes. The technique is demonstrated by example with SigFit, a commercially available tool integrating mechanical analysis with optical analysis.

WFIRST: Coronagraph Systems Engineering and Performance Budgets

NASA Astrophysics Data System (ADS)

Poberezhskiy, Ilya; cady, eric; Frerking, Margaret A.; Kern, Brian; Nemati, Bijan; Noecker, Martin; Seo, Byoung-Joon; Zhao, Feng; Zhou, Hanying

2018-01-01

The WFIRST coronagraph instrument (CGI) will be the first in-space coronagraph using active wavefront control to directly image and characterize mature exoplanets and zodiacal disks in reflected starlight. For CGI systems engineering, including requirements development, CGI performance is predicted using a hierarchy of performance budgets to estimate various noise components — spatial and temporal flux variations — that obscure exoplanet signals in direct imaging and spectroscopy configurations. These performance budgets are validated through a robust integrated modeling and testbed model validation efforts.We present the performance budgeting framework used by WFIRST for the flow-down of coronagraph science requirements, mission constraints, and observatory interfaces to measurable instrument engineering parameters.

High-speed wavefront control using MEMS micromirrors

NASA Astrophysics Data System (ADS)

Bifano, T. G.; Stewart, J. B.

2005-08-01

Over the past decade, a number of electrostatically-actuated MEMS deformable mirror devices have been used for adaptive control in beam-forming and imaging applications. One architecture that has been widely used is the silicon device developed by Boston University, consisting of a continuous or segmented mirror supported by post attachments to an array of parallel plate electrostatic actuators. MEMS deformable mirrors and segmented mirrors with up to 1024 of these actuators have been used in open loop and closed loop control systems to control wavefront errors. Frame rates as high as 11kHz have been demonstrated. Mechanically, the actuators used in this device exhibit a first-mode resonant frequency that is in the range of many tens of kilohertz up to a few hundred kilohertz. Viscous air damping has been found to limit operation at such high frequencies in air at standard pressure. Some applications in high-speed tracking and beam-forming could benefit from increased speed. In this paper, several approaches to achieving critically-damped performance with such MEMS DMs are detailed, and theoretical and experimental results are presented. One approach is to seal the MEMS DM in a full or partial vacuum environment, thereby affecting air damping. After vacuum sealing the device's predicted resonant behavior at tens of kilohertz was observed. In vacuum, the actuator's intrinsic material damping is quite small, resulting in considerable oscillation in step response. To alleviate this problem, a two-step actuation algorithm was employed. Precise control of a single actuator frequencies up to 100kHz without overshoot was demonstrated using this approach. Another approach to increasing actuation speed was to design actuators that reduce air damping effects. This is also demonstrated in the paper.

Research on the adaptive optical control technology based on DSP

NASA Astrophysics Data System (ADS)

Zhang, Xiaolu; Xue, Qiao; Zeng, Fa; Zhao, Junpu; Zheng, Kuixing; Su, Jingqin; Dai, Wanjun

2018-02-01

Adaptive optics is a real-time compensation technique using high speed support system for wavefront errors caused by atmospheric turbulence. However, the randomness and instantaneity of atmospheric changing introduce great difficulties to the design of adaptive optical systems. A large number of complex real-time operations lead to large delay, which is an insurmountable problem. To solve this problem, hardware operation and parallel processing strategy are proposed, and a high-speed adaptive optical control system based on DSP is developed. The hardware counter is used to check the system. The results show that the system can complete a closed loop control in 7.1ms, and improve the controlling bandwidth of the adaptive optical system. Using this system, the wavefront measurement and closed loop experiment are carried out, and obtain the good results.

Wavefront Sensing and Control Technology for Submillimeter and Far-Infrared Space Telescopes

NASA Technical Reports Server (NTRS)

Redding, Dave

2004-01-01

The NGST wavefront sensing and control system will be developed to TRL6 over the next few years, including testing in a cryogenic vacuum environment with traceable hardware. Doing this in the far-infrared and submillimeter is probably easier, as some aspects of the problem scale with wavelength, and the telescope is likely to have a more stable environment; however, detectors may present small complications. Since this is a new system approach, it warrants a new look. For instance, a large space telescope based on the DART membrane mirror design requires a new actuation approach. Other mirror and actuation technologies may prove useful as well.

High-Contrast Coronagraph Performance in the Presence of DM Actuator Defects

NASA Technical Reports Server (NTRS)

Sidick, Erkin; Shaklan, Stuart; Cady, Eric

2015-01-01

Deformable Mirrors (DMs) are critical elements in high contrast coronagraphs, requiring precision and stability measured in picometers to enable detection of Earth-like exoplanets. Occasionally DM actuators or their associated cables or electronics fail, requiring a wavefront control algorithm to compensate for actuators that may be displaced from their neighbors by hundreds of nanometers. We have carried out experiments on our High-Contrast Imaging Testbed (HCIT) to study the impact of failed actuators in partial fulfillment of the Terrestrial Planet Finder Coronagraph optical model validation milestone. We show that the wavefront control algorithm adapts to several broken actuators and maintains dark-hole contrast in broadband light.

High-contrast coronagraph performance in the presence of DM actuator defects

NASA Astrophysics Data System (ADS)

Sidick, Erkin; Shaklan, Stuart; Cady, Eric

2015-09-01

Deformable Mirrors (DMs) are critical elements in high contrast coronagraphs, requiring precision and stability measured in picometers to enable detection of Earth-like exoplanets. Occasionally DM actuators or their associated cables or electronics fail, requiring a wavefront control algorithm to compensate for actuators that may be displaced from their neighbors by hundreds of nanometers. We have carried out experiments on our High-Contrast Imaging Testbed (HCIT) to study the impact of failed actuators in partial fulfilment of the Terrestrial Planet Finder Coronagraph optical model validation milestone. We show that the wavefront control algorithm adapts to several broken actuators and maintains dark-hole contrast in broadband light.

Design and fabrication of reflective spatial light modulator for high-dynamic-range wavefront control

NASA Astrophysics Data System (ADS)

Zhu, Hao; Bierden, Paul; Cornelissen, Steven; Bifano, Thomas; Kim, Jin-Hong

2004-10-01

This paper describes design and fabrication of a microelectromechanical metal spatial light modulator (SLM) integrated with complementary metal-oxide semiconductor (CMOS) electronics, for high-dynamic-range wavefront control. The metal SLM consists of a large array of piston-motion MEMS mirror segments (pixels) which can deflect up to 0.78 µm each. Both 32x32 and 150x150 arrays of the actuators (1024 and 22500 elements respectively) were fabricated onto the CMOS driver electronics and individual pixels were addressed. A new process has been developed to reduce the topography during the metal MEMS processing to fabricate mirror pixels with improved optical quality.

Polarization-independent silicon metadevices for efficient optical wavefront control

DOE PAGES

Chong, Katie E.; Staude, Isabelle; James, Anthony Randolph; ...

2015-07-20

In this study, we experimentally demonstrate a functional silicon metadevice at telecom wavelengths that can efficiently control the wavefront of optical beams by imprinting a spatially varying transmittance phase independent of the polarization of the incident beam. Near-unity transmittance efficiency and close to 0–2π phase coverage are enabled by utilizing the localized electric and magnetic Mie-type resonances of low-loss silicon nanoparticles tailored to behave as electromagnetically dual-symmetric scatterers. We apply this concept to realize a metadevice that converts a Gaussian beam into a vortex beam. The required spatial distribution of transmittance phases is achieved by a variation of the latticemore » spacing as a single geometric control parameter.« less

Polarization-independent silicon metadevices for efficient optical wavefront control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chong, Katie E.; Staude, Isabelle; James, Anthony Randolph

In this study, we experimentally demonstrate a functional silicon metadevice at telecom wavelengths that can efficiently control the wavefront of optical beams by imprinting a spatially varying transmittance phase independent of the polarization of the incident beam. Near-unity transmittance efficiency and close to 0–2π phase coverage are enabled by utilizing the localized electric and magnetic Mie-type resonances of low-loss silicon nanoparticles tailored to behave as electromagnetically dual-symmetric scatterers. We apply this concept to realize a metadevice that converts a Gaussian beam into a vortex beam. The required spatial distribution of transmittance phases is achieved by a variation of the latticemore » spacing as a single geometric control parameter.« less

Wavefront sensor and wavefront corrector matching in adaptive optics

PubMed Central

Dubra, Alfredo

2016-01-01

Matching wavefront correctors and wavefront sensors by minimizing the condition number and mean wavefront variance is proposed. The particular cases of two continuous-sheet deformable mirrors and a Shack-Hartmann wavefront sensor with square packing geometry are studied in the presence of photon noise, background noise and electronics noise. Optimal number of lenslets across each actuator are obtained for both deformable mirrors, and a simple experimental procedure for optimal alignment is described. The results show that high-performance adaptive optics can be achieved even with low cost off-the-shelf Shack-Hartmann arrays with lenslet spacing that do not necessarily match those of the wavefront correcting elements. PMID:19532513

Wavefront sensor and wavefront corrector matching in adaptive optics.

PubMed

Dubra, Alfredo

2007-03-19

Matching wavefront correctors and wavefront sensors by minimizing the condition number and mean wavefront variance is proposed. The particular cases of two continuous-sheet deformable mirrors and a Shack-Hartmann wavefront sensor with square packing geometry are studied in the presence of photon noise, background noise and electronics noise. Optimal number of lenslets across each actuator are obtained for both deformable mirrors, and a simple experimental procedure for optimal alignment is described. The results show that high-performance adaptive optics can be achieved even with low cost off-the-shelf Shack-Hartmann arrays with lenslet spacing that do not necessarily match those of the wavefront correcting elements.

Plasma channels during filamentation of a femtosecond laser pulse with wavefront astigmatism in air

NASA Astrophysics Data System (ADS)

Dergachev, A. A.; Ionin, A. A.; Kandidov, V. P.; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Shlenov, S. A.; Shustikova, A. P.

2014-12-01

We have demonstrated experimentally and numerically the possibility of controlling parameters of plasma channels formed during filamentation of a femtosecond laser pulse by introducing astigmatism in the laser beam wavefront. It is found that weak astigmatism increases the length of the plasma channel in comparison with the case of aberration-free focusing and that strong astigmatism can cause splitting of the plasma channel into two channels located one after another on the filament axis.

Thermally induced distortion of a high-average-power laser system by an optical transport system

NASA Astrophysics Data System (ADS)

Chow, Robert; Ault, Linda E.; Taylor, John R.; Jedlovec, Don

1999-11-01

The atomic vapor laser isotope separation process uses high- average power lasers that have the commercial potential to enrich uranium for the electric power utilities. The transport of the laser beam through the laser system to the separation chambers requires high performance optical components, most of which have either fused silica or Zerodur as the substrate material. One of the requirements of the optical components is to preserve the wavefront quality of the laser beam that propagate over long distances. Full aperture tests with the high power process lasers and finite element analysis (FEA) have been performed on the transport optics. The wavefront distortions of the various sections of the transport path were measured with diagnostic Hartmann sensor packages. The FEA results were derived from an in-house thermal-structural- optical code which is linked to the commercially available CodeV program. In comparing the measured and predicted results, the bulk absorptance of fused silica was estimated to about 50 ppm/cm in the visible wavelength regime. Wavefront distortions will be reported on optics made from fused silica and Zerodur substrate materials.

One-year eye-to-eye comparison of wavefront-guided versus wavefront-optimized laser in situ keratomileusis in hyperopes

PubMed Central

Sáles, Christopher S; Manche, Edward E

2014-01-01

Background To compare wavefront (WF)-guided and WF-optimized laser in situ keratomileusis (LASIK) in hyperopes with respect to the parameters of safety, efficacy, predictability, refractive error, uncorrected distance visual acuity, corrected distance visual acuity, contrast sensitivity, and higher order aberrations. Methods Twenty-two eyes of eleven participants with hyperopia with or without astigmatism were prospectively randomized to receive WF-guided LASIK with the VISX CustomVue S4 IR or WF-optimized LASIK with the WaveLight Allegretto Eye-Q 400 Hz. LASIK flaps were created using the 150-kHz IntraLase iFS. Evaluations included measurement of uncorrected distance visual acuity, corrected distance visual acuity, <5% and <25% contrast sensitivity, and WF aberrometry. Patients also completed a questionnaire detailing symptoms on a quantitative grading scale. Results There were no statistically significant differences between the groups for any of the variables studied after 12 months of follow-up (all P>0.05). Conclusion This comparative case series of 11 subjects with hyperopia showed that WF-guided and WF-optimized LASIK had similar clinical outcomes at 12 months. PMID:25419115

Research in the Optical Sciences.

DTIC Science & Technology

1987-12-15

been chosen for the wavefront sensor. REFERENCES 1. C. L. Koliopoulos, " Wavefront sensing of the turbulent atmosphere using a lateral shearing...technique would permit wavefront sensing in the image plane without employing an elaborate method to obtain a reference wavefront . Background Initial...and R. H. Potoff ......... 87 0rd . . .. El WAVEFRONT SENSING AND ADAPTIVE OPTICS C . K oliopoulos ............................................. 97

Determining the wedge angle and optical homogeneity of a glass plate by statistically analyzing the deformation in the wavefront surface.

PubMed

Yang, Pao-Keng

2017-08-01

By using a light-emitting diode as the probing light source and a Shack-Hartmann wavefront sensor as the recorder for the wavefront surface to execute a relative measurement, we present a useful method for determining the small wedge angle and optical homogeneity of a nominally planar glass plate from the wavefront measurements. The measured wavefront surface from the light source was first calibrated to be a horizontal plane before the plate under test was inserted. The wedge angle of the plate can be determined from the inclining angle of the regression plane of the measured wavefront surface after the plate was inserted between the light source and the wavefront sensor. Despite the annoying time-dependent altitude fluctuation in measured wavefront topography, the optical homogeneity of the plate can be estimated from the increment on the average variance of the wavefront surface to its regression plane after the light passes through it by using the Bienaymé formula.

Method and apparatus for assessing material properties of sheet-like materials

DOEpatents

Telschow, Kenneth L.; Deason, Vance A.

2002-01-01

Apparatus for producing an indication of a material property of a sheet-like material according to the present invention may comprise an excitation source for vibrating the sheet-like material to produce at least one traveling wave therein. A light source configured to produce an object wavefront and a reference wavefront directs the object wavefront toward the sheet-like material to produce a modulated object wavefront. A modulator operatively associated with the reference wavefront modulates the reference wavefront in synchronization with the traveling wave on the sheet-like material to produce a modulated reference wavefront. A sensing medium positioned to receive the modulated object wavefront and the modulated reference wavefront produces an image of the traveling wave in the sheet-like material, the image of the anti-symmetric traveling wave being related to a displacement amplitude of the anti-symmetric traveling wave over a two-dimensional area of the vibrating sheet-like material. A detector detects the image of the traveling wave in the sheet-like material.

Dual-mode photosensitive arrays based on the integration of liquid crystal microlenses and CMOS sensors for obtaining the intensity images and wavefronts of objects.

PubMed

Tong, Qing; Lei, Yu; Xin, Zhaowei; Zhang, Xinyu; Sang, Hongshi; Xie, Changsheng

2016-02-08

In this paper, we present a kind of dual-mode photosensitive arrays (DMPAs) constructed by hybrid integration a liquid crystal microlens array (LCMLA) driven electrically and a CMOS sensor array, which can be used to measure both the conventional intensity images and corresponding wavefronts of objects. We utilize liquid crystal materials to shape the microlens array with the electrically tunable focal length. Through switching the voltage signal on and off, the wavefronts and the intensity images can be acquired through the DMPAs, sequentially. We use white light to obtain the object's wavefronts for avoiding losing important wavefront information. We separate the white light wavefronts with a large number of spectral components and then experimentally compare them with single spectral wavefronts of typical red, green and blue lasers, respectively. Then we mix the red, green and blue wavefronts to a composite wavefront containing more optical information of the object.

Method and apparatus for detecting internal structures of bulk objects using acoustic imaging

DOEpatents

Deason, Vance A.; Telschow, Kenneth L.

2002-01-01

Apparatus for producing an acoustic image of an object according to the present invention may comprise an excitation source for vibrating the object to produce at least one acoustic wave therein. The acoustic wave results in the formation of at least one surface displacement on the surface of the object. A light source produces an optical object wavefront and an optical reference wavefront and directs the optical object wavefront toward the surface of the object to produce a modulated optical object wavefront. A modulator operatively associated with the optical reference wavefront modulates the optical reference wavefront in synchronization with the acoustic wave to produce a modulated optical reference wavefront. A sensing medium positioned to receive the modulated optical object wavefront and the modulated optical reference wavefront combines the modulated optical object and reference wavefronts to produce an image related to the surface displacement on the surface of the object. A detector detects the image related to the surface displacement produced by the sensing medium. A processing system operatively associated with the detector constructs an acoustic image of interior features of the object based on the phase and amplitude of the surface displacement on the surface of the object.

High-contrast imager for Complex Aperture Telescopes (HiCAT): APLC/shaped-pupil hybrid coronagraph designs

NASA Astrophysics Data System (ADS)

N'Diaye, Mamadou; Choquet, Elodie; Carlotti, Alexis; Pueyo, Laurent; Egron, Sylvain; Leboulleux, Lucie; Levecq, Olivier; Perrin, Marshall D.; Wallace, J. Kent; Long, Chris; Lajoie, Rachel; Lajoie, Charles-Philippe; Eldorado Riggs, A. J.; Zimmerman, Neil T.; Groff, Tyler Dean; Kasdin, N. Jeremy; Vanderbei, Robert J.; Mawet, Dimitri; Macintosh, Bruce; Shaklan, Stuart; Soummer, Remi

2015-01-01

HiCAT is a high-contrast imaging testbed designed to provide complete solutions in wavefront sensing, control and starlight suppression with complex aperture telescopes. Primary mirror segmentation, central obstruction and spiders in the pupil of an on-axis telescope introduces additional diffraction features in the point spread function, which make high-contrast imaging very challenging. The testbed alignment was completed in the summer of 2014, exceeding specifications with a total wavefront error of 12nm rms with a 18mm pupil. Two deformable mirrors are to be installed for wavefront control in the fall of 2014. In this communication, we report on the first testbed results using a classical Lyot coronagraph. We have developed novel coronagraph designs combining an Apodized Pupil Lyot Coronagraph (APLC) with shaped-pupil type optimizations. We present the results of these new APLC-type solutions with two-dimensional shaped-pupil apodizers for the HiCAT geometry. These solutions render the system quasi-insensitive to jitter and low-order aberrations, while improving the performance in terms of inner working angle, bandpass and contrast over a classical APLC.

Adaptive optics compensation over a 3 km near horizontal path

NASA Astrophysics Data System (ADS)

Mackey, Ruth; Dainty, Chris

2008-10-01

We present results of adaptive optics compensation at the receiver of a 3km optical link using a beacon laser operating at 635nm. The laser is transmitted from the roof of a seven-storey building over a near horizontal path towards a 127 mm optical receiver located on the second-floor of the Applied Optics Group at the National University of Ireland, Galway. The wavefront of the scintillated beam is measured using a Shack-Hartmann wavefront sensor (SHWFS) with high-speed CMOS camera capable of frame rates greater than 1kHz. The strength of turbulence is determined from the fluctuations in differential angle-of-arrival in the wavefront sensor measurements and from the degree of scintillation in the pupil plane. Adaptive optics compensation is applied using a tip-tilt mirror and 37 channel membrane mirror and controlled using a single desktop computer. The performance of the adaptive optics system in real turbulence is compared with the performance of the system in a controlled laboratory environment, where turbulence is generated using a liquid crystal spatial light modulator.

Correcting the wavefront aberration of membrane mirror based on liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Yang, Bin; Wei, Yin; Chen, Xinhua; Tang, Minxue

2014-11-01

Membrane mirror with flexible polymer film substrate is a new-concept ultra lightweight mirror for space applications. Compared with traditional mirrors, membrane mirror has the advantages of lightweight, folding and deployable, low cost and etc. Due to the surface shape of flexible membrane mirror is easy to deviate from the design surface shape, it will bring wavefront aberration to the optical system. In order to solve this problem, a method of membrane mirror wavefront aberration correction based on the liquid crystal spatial light modulator (LCSLM) will be studied in this paper. The wavefront aberration correction principle of LCSLM is described and the phase modulation property of a LCSLM is measured and analyzed firstly. Then the membrane mirror wavefront aberration correction system is designed and established according to the optical properties of a membrane mirror. The LCSLM and a Hartmann-Shack sensor are used as a wavefront corrector and a wavefront detector, respectively. The detected wavefront aberration is calculated and converted into voltage value on LCSLM for the mirror wavefront aberration correction by programming in Matlab. When in experiment, the wavefront aberration of a glass plane mirror with a diameter of 70 mm is measured and corrected for verifying the feasibility of the experiment system and the correctness of the program. The PV value and RMS value of distorted wavefront are reduced and near diffraction limited optical performance is achieved. On this basis, the wavefront aberration of the aperture center Φ25 mm in a membrane mirror with a diameter of 200 mm is corrected and the errors are analyzed. It provides a means of correcting the wavefront aberration of membrane mirror.

Piezocomposite Actuator Arrays for Correcting and Controlling Wavefront Error in Reflectors

NASA Technical Reports Server (NTRS)

Bradford, Samuel Case; Peterson, Lee D.; Ohara, Catherine M.; Shi, Fang; Agnes, Greg S.; Hoffman, Samuel M.; Wilkie, William Keats

2012-01-01

Three reflectors have been developed and tested to assess the performance of a distributed network of piezocomposite actuators for correcting thermal deformations and total wave-front error. The primary testbed article is an active composite reflector, composed of a spherically curved panel with a graphite face sheet and aluminum honeycomb core composite, and then augmented with a network of 90 distributed piezoelectric composite actuators. The piezoelectric actuator system may be used for correcting as-built residual shape errors, and for controlling low-order, thermally-induced quasi-static distortions of the panel. In this study, thermally-induced surface deformations of 1 to 5 microns were deliberately introduced onto the reflector, then measured using a speckle holography interferometer system. The reflector surface figure was subsequently corrected to a tolerance of 50 nm using the actuators embedded in the reflector's back face sheet. Two additional test articles were constructed: a borosilicate at window at 150 mm diameter with 18 actuators bonded to the back surface; and a direct metal laser sintered reflector with spherical curvature, 230 mm diameter, and 12 actuators bonded to the back surface. In the case of the glass reflector, absolute measurements were performed with an interferometer and the absolute surface was corrected. These test articles were evaluated to determine their absolute surface control capabilities, as well as to assess a multiphysics modeling effort developed under this program for the prediction of active reflector response. This paper will describe the design, construction, and testing of active reflector systems under thermal loads, and subsequent correction of surface shape via distributed peizeoelctric actuation.

Myopic aberrations: Simulation based comparison of curvature and Hartmann Shack wavefront sensors

NASA Astrophysics Data System (ADS)

Basavaraju, Roopashree M.; Akondi, Vyas; Weddell, Stephen J.; Budihal, Raghavendra Prasad

2014-02-01

In comparison with a Hartmann Shack wavefront sensor, the curvature wavefront sensor is known for its higher sensitivity and greater dynamic range. The aim of this study is to numerically investigate the merits of using a curvature wavefront sensor, in comparison with a Hartmann Shack (HS) wavefront sensor, to analyze aberrations of the myopic eye. Aberrations were statistically generated using Zernike coefficient data of 41 myopic subjects obtained from the literature. The curvature sensor is relatively simple to implement, and the processing of extra- and intra-focal images was linearly resolved using the Radon transform to provide Zernike modes corresponding to statistically generated aberrations. Simulations of the HS wavefront sensor involve the evaluation of the focal spot pattern from simulated aberrations. Optical wavefronts were reconstructed using the slope geometry of Southwell. Monte Carlo simulation was used to find critical parameters for accurate wavefront sensing and to investigate the performance of HS and curvature sensors. The performance of the HS sensor is highly dependent on the number of subapertures and the curvature sensor is largely dependent on the number of Zernike modes used to represent the aberration and the effective propagation distance. It is shown that in order to achieve high wavefront sensing accuracy while measuring aberrations of the myopic eye, a simpler and cost effective curvature wavefront sensor is a reliable alternative to a high resolution HS wavefront sensor with a large number of subapertures.

Woofer-tweeter adaptive optics scanning laser ophthalmoscopic imaging based on Lagrange-multiplier damped least-squares algorithm.

PubMed

Zou, Weiyao; Qi, Xiaofeng; Burns, Stephen A

2011-07-01

We implemented a Lagrange-multiplier (LM)-based damped least-squares (DLS) control algorithm in a woofer-tweeter dual deformable-mirror (DM) adaptive optics scanning laser ophthalmoscope (AOSLO). The algorithm uses data from a single Shack-Hartmann wavefront sensor to simultaneously correct large-amplitude low-order aberrations by a woofer DM and small-amplitude higher-order aberrations by a tweeter DM. We measured the in vivo performance of high resolution retinal imaging with the dual DM AOSLO. We compared the simultaneous LM-based DLS dual DM controller with both single DM controller, and a successive dual DM controller. We evaluated performance using both wavefront (RMS) and image quality metrics including brightness and power spectrum. The simultaneous LM-based dual DM AO can consistently provide near diffraction-limited in vivo routine imaging of human retina.

Enabling Super-Nyquist Wavefront Control on WFIRST

NASA Astrophysics Data System (ADS)

Bendek, Eduardo; Belikov, Ruslan; Sirbu, Dan; Shaklan, Stuart B.; Eldorado Riggs, A. J.

2018-01-01

A large fraction of sun-like stars is contained in Binary systems. Within 10pc there are 70 FGK stars from which, 43 belong to a multi-star system, and 28 of them have companion leak that is greater than 1e-9 contrast assuming typical Hubble-quality space optics. Currently, those binary stars are not included in the WFIRST-CGI target list, but they could be observed if high-contrast imaging around binary star systems using WFIRST is possible, increasing by 70% the number of possible FGK targets for the mission. The Multi-Star Wavefront Control (MSWC) algorithm can be used to suppress the companion star leakage. If the targets have angular separations larger than the Nyquist controllable region of the Deformable Mirror the MSWC must operate in its Super-Nyquist (SN) mode. This mode requires a target star replica within the SN region in order to provide the energy, and coherent light necessary to null speckles at SN angular separations. For the case of WFIRST, about half of the targets that can be observed using MSWC have angular separations larger than the Nyquist controllable region of the 48x48 actuator Deformable Mirror (DM) to be used. Here, we discuss multiple alternatives to generate those PSF replicas with minimal or no impact to the WFIRST Coronagraph instrument such as 1) the addition of a movable diffractive pupil mounted of the Shape Pupil wheel. 2) Design of a modified Shape Pupil design able to create a dark zone and at the same time diffract a small fraction of the starlight on the SN region. 3) Predict the minimum residual quilting on Xinetics DM that would allow observing a given target.

Evaluation of iris recognition system for wavefront-guided laser in situ keratomileusis for myopic astigmatism.

PubMed

Ghosh, Sudipta; Couper, Terry A; Lamoureux, Ecosse; Jhanji, Vishal; Taylor, Hugh R; Vajpayee, Rasik B

2008-02-01

To evaluate the visual and refractive outcomes of wavefront-guided laser in situ keratomileusis (LASIK) using an iris recognition system for the correction of myopic astigmatism. Centre for Eye Research Australia, Melbourne Excimer Laser Research Group, and Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia. A comparative analysis of wavefront-guided LASIK was performed with an iris recognition system (iris recognition group) and without iris recognition (control group). The main parameters were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity, amount of residual cylinder, manifest spherical equivalent (SE), and the index of success using the Alpins method of astigmatism analysis 1 and 3 months postoperatively. A P value less than 0.05 was considered statistically significant. Preoperatively, the mean SE was -4.32 diopters (D) +/- 1.59 (SD) in the iris recognition group (100 eyes) and -4.55 +/- 1.87 D in the control group (98 eyes) (P = .84). At 3 months, the mean SE was -0.05 +/- 0.21 D and -0.20 +/- 0.40 D, respectively (P = .001), and an SE within +/-0.50 D of emmetropia was achieved in 92.0% and 85.7% of eyes, respectively (P = .07). At 3 months, the UCVA was 20/20 or better in 90.0% and 76.5% of eyes, respectively. A statistically significant difference in the amount of astigmatic correction was seen between the 2 groups (P = .00 and P = .01 at 1 and 3 months, respectively). The index of success was 98.0% in the iris recognition group and 81.6% in the control group (P = .03). Iris recognition software may achieve better visual and refractive outcomes in wavefront-guided LASIK for myopic astigmatism.

Wavefront sensorless adaptive optics versus sensor-based adaptive optics for in vivo fluorescence retinal imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wahl, Daniel J.; Zhang, Pengfei; Jian, Yifan; Bonora, Stefano; Sarunic, Marinko V.; Zawadzki, Robert J.

2017-02-01

Adaptive optics (AO) is essential for achieving diffraction limited resolution in large numerical aperture (NA) in-vivo retinal imaging in small animals. Cellular-resolution in-vivo imaging of fluorescently labeled cells is highly desirable for studying pathophysiology in animal models of retina diseases in pre-clinical vision research. Currently, wavefront sensor-based (WFS-based) AO is widely used for retinal imaging and has demonstrated great success. However, the performance can be limited by several factors including common path errors, wavefront reconstruction errors and an ill-defined reference plane on the retina. Wavefront sensorless (WFS-less) AO has the advantage of avoiding these issues at the cost of algorithmic execution time. We have investigated WFS-less AO on a fluorescence scanning laser ophthalmoscopy (fSLO) system that was originally designed for WFS-based AO. The WFS-based AO uses a Shack-Hartmann WFS and a continuous surface deformable mirror in a closed-loop control system to measure and correct for aberrations induced by the mouse eye. The WFS-less AO performs an open-loop modal optimization with an image quality metric. After WFS-less AO aberration correction, the WFS was used as a control of the closed-loop WFS-less AO operation. We can easily switch between WFS-based and WFS-less control of the deformable mirror multiple times within an imaging session for the same mouse. This allows for a direct comparison between these two types of AO correction for fSLO. Our results demonstrate volumetric AO-fSLO imaging of mouse retinal cells labeled with GFP. Most significantly, we have analyzed and compared the aberration correction results for WFS-based and WFS-less AO imaging.

Generalised optical differentiation wavefront sensor: a sensitive high dynamic range wavefront sensor.

PubMed

Haffert, S Y

2016-08-22

Current wavefront sensors for high resolution imaging have either a large dynamic range or a high sensitivity. A new kind of wavefront sensor is developed which can have both: the Generalised Optical Differentiation wavefront sensor. This new wavefront sensor is based on the principles of optical differentiation by amplitude filters. We have extended the theory behind linear optical differentiation and generalised it to nonlinear filters. We used numerical simulations and laboratory experiments to investigate the properties of the generalised wavefront sensor. With this we created a new filter that can decouple the dynamic range from the sensitivity. These properties make it suitable for adaptive optic systems where a large range of phase aberrations have to be measured with high precision.

Framework to trade optimality for local processing in large-scale wavefront reconstruction problems.

PubMed

Haber, Aleksandar; Verhaegen, Michel

2016-11-15

We show that the minimum variance wavefront estimation problems permit localized approximate solutions, in the sense that the wavefront value at a point (excluding unobservable modes, such as the piston mode) can be approximated by a linear combination of the wavefront slope measurements in the point's neighborhood. This enables us to efficiently compute a wavefront estimate by performing a single sparse matrix-vector multiplication. Moreover, our results open the possibility for the development of wavefront estimators that can be easily implemented in a decentralized/distributed manner, and in which the estimate optimality can be easily traded for computational efficiency. We numerically validate our approach on Hudgin wavefront sensor geometries, and the results can be easily generalized to Fried geometries.

Investigation of the confocal wavefront sensor and its application to biological microscopy.

PubMed

Shaw, Michael; O'Holleran, Kevin; Paterson, Carl

2013-08-12

Wavefront sensing in the presence of background light sources is complicated by the need to restrict the effective depth of field of the wavefront sensor. This problem is particularly significant in direct wavefront sensing adaptive optic (AO) schemes for correcting imaging aberrations in biological microscopy. In this paper we investigate how a confocal pinhole can be used to reject out of focus light whilst still allowing effective wavefront sensing. Using a scaled set of phase screens with statistical properties derived from measurements of wavefront aberrations induced by C. elegans specimens, we investigate and quantify how the size of the pinhole and the aberration amplitude affect the transmitted wavefront. We suggest a lower bound for the pinhole size for a given aberration strength and quantify the optical sectioning provided by the system. For our measured aberration data we find that a pinhole of size approximately 3 Airy units represents a good compromise, allowing effective transmission of the wavefront and thin optical sections. Finally, we discuss some of the practical implications of confocal wavefront sensing for AO systems in microscopy.

TRL-6 for JWST wavefront sensing and control

NASA Astrophysics Data System (ADS)

Feinberg, Lee D.; Dean, Bruce H.; Aronstein, David L.; Bowers, Charles W.; Hayden, William; Lyon, Richard G.; Shiri, Ron; Smith, J. Scott; Acton, D. Scott; Carey, Larkin; Contos, Adam; Sabatke, Erin; Schwenker, John; Shields, Duncan; Towell, Tim; Shi, Fang; Meza, Luis

2007-09-01

NASA's Technology Readiness Level (TRL)-6 is documented for the James Webb Space Telescope (JWST) Wavefront Sensing and Control (WFSC) subsystem. The WFSC subsystem is needed to align the Optical Telescope Element (OTE) after all deployments have occurred, and achieves that requirement through a robust commissioning sequence consisting of unique commissioning algorithms, all of which are part of the WFSC algorithm suite. This paper identifies the technology need, algorithm heritage, describes the finished TRL-6 design platform, and summarizes the TRL-6 test results and compliance. Additionally, the performance requirements needed to satisfy JWST science goals as well as the criterion that relate to the TRL-6 Testbed Telescope (TBT) performance requirements are discussed.

TRL-6 for JWST Wavefront Sensing and Control

NASA Technical Reports Server (NTRS)

Feinberg, Lee; Dean, Bruce; Smith, Scott; Aronstein, David; Shiri, Ron; Lyon, Rick; Hayden, Bill; Bowers, Chuck; Acton, D. Scott; Shields, Duncan;

Optimization of two-photon wave function in parametric down conversion by adaptive optics control of the pump radiation.

PubMed

Minozzi, M; Bonora, S; Sergienko, A V; Vallone, G; Villoresi, P

2013-02-15

We present an efficient method for optimizing the spatial profile of entangled-photon wave function produced in a spontaneous parametric down conversion process. A deformable mirror that modifies a wavefront of a 404 nm CW diode laser pump interacting with a nonlinear β-barium borate type-I crystal effectively controls the profile of the joint biphoton function. The use of a feedback signal extracted from the biphoton coincidence rate is used to achieve the optimal wavefront shape. The optimization of the two-photon coupling into two, single spatial modes for correlated detection is used for a practical demonstration of this physical principle.

Wavefront Control and Image Restoration with Less Computing

NASA Technical Reports Server (NTRS)

Lyon, Richard G.

2010-01-01

PseudoDiversity is a method of recovering the wavefront in a sparse- or segmented- aperture optical system typified by an interferometer or a telescope equipped with an adaptive primary mirror consisting of controllably slightly moveable segments. (PseudoDiversity should not be confused with a radio-antenna-arraying method called pseudodiversity.) As in the cases of other wavefront- recovery methods, the streams of wavefront data generated by means of PseudoDiversity are used as feedback signals for controlling electromechanical actuators of the various segments so as to correct wavefront errors and thereby, for example, obtain a clearer, steadier image of a distant object in the presence of atmospheric turbulence. There are numerous potential applications in astronomy, remote sensing from aircraft and spacecraft, targeting missiles, sighting military targets, and medical imaging (including microscopy) through such intervening media as cells or water. In comparison with prior wavefront-recovery methods used in adaptive optics, PseudoDiversity involves considerably simpler equipment and procedures and less computation. For PseudoDiversity, there is no need to install separate metrological equipment or to use any optomechanical components beyond those that are already parts of the optical system to which the method is applied. In Pseudo- Diversity, the actuators of a subset of the segments or subapertures are driven to make the segments dither in the piston, tilt, and tip degrees of freedom. Each aperture is dithered at a unique frequency at an amplitude of a half wavelength of light. During the dithering, images on the focal plane are detected and digitized at a rate of at least four samples per dither period. In the processing of the image samples, the use of different dither frequencies makes it possible to determine the separate effects of the various dithered segments or apertures. The digitized image-detector outputs are processed in the spatial-frequency (Fourier-transform) domain to obtain measures of the piston, tip, and tilt errors over each segment or subaperture. Once these measures are known, they are fed back to the actuators to correct the errors. In addition, measures of errors that remain after correction by use of the actuators are further utilized in an algorithm in which the image is phase-corrected in the spatial-frequency domain and then transformed back to the spatial domain at each time step and summed with the images from all previous time steps to obtain a final image having a greater signal-to-noise ratio (and, hence, a visual quality) higher than would otherwise be attainable.

Apparatus and method for measuring and imaging traveling waves

DOEpatents

Telschow, Kenneth L.; Deason, Vance A.

2001-01-01

An apparatus is provided for imaging traveling waves in a medium. The apparatus includes a vibration excitation source configured to impart traveling waves within a medium. An emitter is configured to produce two or more wavefronts, at least one wavefront modulated by a vibrating medium. A modulator is configured to modulate another wavefront in synchronization with the vibrating medium. A sensing media is configured to receive in combination the modulated one wavefront and the another wavefront and having a detection resolution within a limited bandwidth. The another wavefront is modulated at a frequency such that a difference frequency between the one wavefront and the another wavefront is within a response range of the sensing media. Such modulation produces an image of the vibrating medium having an output intensity that is substantially linear with small physical variations within the vibrating medium for all vibration frequencies above the sensing media's response bandwidth. A detector is configured to detect an image of traveling waves in the vibrating medium resulting from interference between the modulated one wavefront and the another wavefront when combined in association with the sensing media. The traveling wave can be used to characterize certain material properties of the medium. Furthermore, a method is provided for imaging and characterizing material properties according to the apparatus.

Object-oriented wavefront correction in an asymmetric amplifying high-power laser system

NASA Astrophysics Data System (ADS)

Yang, Ying; Yuan, Qiang; Wang, Deen; Zhang, Xin; Dai, Wanjun; Hu, Dongxia; Xue, Qiao; Zhang, Xiaolu; Zhao, Junpu; Zeng, Fa; Wang, Shenzhen; Zhou, Wei; Zhu, Qihua; Zheng, Wanguo

2018-05-01

An object-oriented wavefront control method is proposed aiming for excellent near-field homogenization and far-field distribution in an asymmetric amplifying high-power laser system. By averaging the residual errors of the propagating beam, smaller pinholes could be employed on the spatial filters to improve the beam quality. With this wavefront correction system, the laser performance of the main amplifier system in the Shen Guang-III laser facility has been improved. The residual wavefront aberration at the position of each pinhole is below 2 µm (peak-to-valley). For each pinhole, 95% of the total laser energy is enclosed within a circle whose diameter is no more than six times the diffraction limit. At the output of the main laser system, the near-field modulation and contrast are 1.29% and 7.5%, respectively, and 95% of the 1ω (1053 nm) beam energy is contained within a 39.8 µrad circle (6.81 times the diffraction limit) under a laser fluence of 5.8 J cm-2. The measured 1ω focal spot size and near-field contrast are better than the design values of the Shen Guang-III laser facility.

Estimation of chromatic errors from broadband images for high contrast imaging

NASA Astrophysics Data System (ADS)

Sirbu, Dan; Belikov, Ruslan

2015-09-01

Usage of an internal coronagraph with an adaptive optical system for wavefront correction for direct imaging of exoplanets is currently being considered for many mission concepts, including as an instrument addition to the WFIRST-AFTA mission to follow the James Web Space Telescope. The main technical challenge associated with direct imaging of exoplanets with an internal coronagraph is to effectively control both the diffraction and scattered light from the star so that the dim planetary companion can be seen. For the deformable mirror (DM) to recover a dark hole region with sufficiently high contrast in the image plane, wavefront errors are usually estimated using probes on the DM. To date, most broadband lab demonstrations use narrowband filters to estimate the chromaticity of the wavefront error, but this reduces the photon flux per filter and requires a filter system. Here, we propose a method to estimate the chromaticity of wavefront errors using only a broadband image. This is achieved by using special DM probes that have sufficient chromatic diversity. As a case example, we simulate the retrieval of the spectrum of the central wavelength from broadband images for a simple shaped- pupil coronagraph with a conjugate DM and compute the resulting estimation error.

Focusing light inside dynamic scattering media with millisecond digital optical phase conjugation

PubMed Central

Liu, Yan; Ma, Cheng; Shen, Yuecheng; Shi, Junhui; Wang, Lihong V.

2017-01-01

Wavefront shaping based on digital optical phase conjugation (DOPC) focuses light through or inside scattering media, but the low speed of DOPC prevents it from being applied to thick, living biological tissue. Although a fast DOPC approach was recently developed, the reported single-shot wavefront measurement method does not work when the goal is to focus light inside, instead of through, highly scattering media. Here, using a ferroelectric liquid crystal based spatial light modulator, we develop a simpler but faster DOPC system that focuses light not only through, but also inside scattering media. By controlling 2.6 × 105 optical degrees of freedom, our system focused light through 3 mm thick moving chicken tissue, with a system latency of 3.0 ms. Using ultrasound-guided DOPC, along with a binary wavefront measurement method, our system focused light inside a scattering medium comprising moving tissue with a latency of 6.0 ms, which is one to two orders of magnitude shorter than those of previous digital wavefront shaping systems. Since the demonstrated speed approaches tissue decorrelation rates, this work is an important step toward in vivo deep-tissue non-invasive optical imaging, manipulation, and therapy. PMID:28815194

Modelling Delta-Notch perturbations during zebrafish somitogenesis.

PubMed

Murray, Philip J; Maini, Philip K; Baker, Ruth E

2013-01-15

The discovery over the last 15 years of molecular clocks and gradients in the pre-somitic mesoderm of numerous vertebrate species has added significant weight to Cooke and Zeeman's 'clock and wavefront' model of somitogenesis, in which a travelling wavefront determines the spatial position of somite formation and the somitogenesis clock controls periodicity (Cooke and Zeeman, 1976). However, recent high-throughput measurements of spatiotemporal patterns of gene expression in different zebrafish mutant backgrounds allow further quantitative evaluation of the clock and wavefront hypothesis. In this study we describe how our recently proposed model, in which oscillator coupling drives the propagation of an emergent wavefront, can be used to provide mechanistic and testable explanations for the following observed phenomena in zebrafish embryos: (a) the variation in somite measurements across a number of zebrafish mutants; (b) the delayed formation of somites and the formation of 'salt and pepper' patterns of gene expression upon disruption of oscillator coupling; and (c) spatial correlations in the 'salt and pepper' patterns in Delta-Notch mutants. In light of our results, we propose a number of plausible experiments that could be used to further test the model. Copyright © 2012 Elsevier Inc. All rights reserved.

A First Order Wavefront Estimation Algorithm for P1640 Calibrator

NASA Technical Reports Server (NTRS)

Zhaia, C.; Vasisht, G.; Shao, M.; Lockhart, T.; Cady, E.; Oppenheimer, B.; Burruss, R.; Roberts, J.; Beichman, C.; Brenner, D.;

Using Spherical-Harmonics Expansions for Optics Surface Reconstruction from Gradients.

PubMed

Solano-Altamirano, Juan Manuel; Vázquez-Otero, Alejandro; Khikhlukha, Danila; Dormido, Raquel; Duro, Natividad

2017-11-30

In this paper, we propose a new algorithm to reconstruct optics surfaces (aka wavefronts) from gradients, defined on a circular domain, by means of the Spherical Harmonics. The experimental results indicate that this algorithm renders the same accuracy, compared to the reconstruction based on classical Zernike polynomials, using a smaller number of polynomial terms, which potentially speeds up the wavefront reconstruction. Additionally, we provide an open-source C++ library, released under the terms of the GNU General Public License version 2 (GPLv2), wherein several polynomial sets are coded. Therefore, this library constitutes a robust software alternative for wavefront reconstruction in a high energy laser field, optical surface reconstruction, and, more generally, in surface reconstruction from gradients. The library is a candidate for being integrated in control systems for optical devices, or similarly to be used in ad hoc simulations. Moreover, it has been developed with flexibility in mind, and, as such, the implementation includes the following features: (i) a mock-up generator of various incident wavefronts, intended to simulate the wavefronts commonly encountered in the field of high-energy lasers production; (ii) runtime selection of the library in charge of performing the algebraic computations; (iii) a profiling mechanism to measure and compare the performance of different steps of the algorithms and/or third-party linear algebra libraries. Finally, the library can be easily extended to include additional dependencies, such as porting the algebraic operations to specific architectures, in order to exploit hardware acceleration features.

Using Spherical-Harmonics Expansions for Optics Surface Reconstruction from Gradients

PubMed Central

Solano-Altamirano, Juan Manuel; Khikhlukha, Danila

2017-01-01

In this paper, we propose a new algorithm to reconstruct optics surfaces (aka wavefronts) from gradients, defined on a circular domain, by means of the Spherical Harmonics. The experimental results indicate that this algorithm renders the same accuracy, compared to the reconstruction based on classical Zernike polynomials, using a smaller number of polynomial terms, which potentially speeds up the wavefront reconstruction. Additionally, we provide an open-source C++ library, released under the terms of the GNU General Public License version 2 (GPLv2), wherein several polynomial sets are coded. Therefore, this library constitutes a robust software alternative for wavefront reconstruction in a high energy laser field, optical surface reconstruction, and, more generally, in surface reconstruction from gradients. The library is a candidate for being integrated in control systems for optical devices, or similarly to be used in ad hoc simulations. Moreover, it has been developed with flexibility in mind, and, as such, the implementation includes the following features: (i) a mock-up generator of various incident wavefronts, intended to simulate the wavefronts commonly encountered in the field of high-energy lasers production; (ii) runtime selection of the library in charge of performing the algebraic computations; (iii) a profiling mechanism to measure and compare the performance of different steps of the algorithms and/or third-party linear algebra libraries. Finally, the library can be easily extended to include additional dependencies, such as porting the algebraic operations to specific architectures, in order to exploit hardware acceleration features. PMID:29189722

Zonal wavefront sensing with enhanced spatial resolution.

PubMed

Pathak, Biswajit; Boruah, Bosanta R

2016-12-01

In this Letter, we introduce a scheme to enhance the spatial resolution of a zonal wavefront sensor. The zonal wavefront sensor comprises an array of binary gratings implemented by a ferroelectric spatial light modulator (FLCSLM) followed by a lens, in lieu of the array of lenses in the Shack-Hartmann wavefront sensor. We show that the fast response of the FLCSLM device facilitates quick display of several laterally shifted binary grating patterns, and the programmability of the device enables simultaneous capturing of each focal spot array. This eventually leads to a wavefront estimation with an enhanced spatial resolution without much sacrifice on the sensor frame rate, thus making the scheme suitable for high spatial resolution measurement of transient wavefronts. We present experimental and numerical simulation results to demonstrate the importance of the proposed wavefront sensing scheme.

Model-based estimation and control for off-axis parabolic mirror alignment

NASA Astrophysics Data System (ADS)

Fang, Joyce; Savransky, Dmitry

2018-02-01

This paper propose an model-based estimation and control method for an off-axis parabolic mirror (OAP) alignment. Current studies in automated optical alignment systems typically require additional wavefront sensors. We propose a self-aligning method using only focal plane images captured by the existing camera. Image processing methods and Karhunen-Loève (K-L) decomposition are used to extract measurements for the observer in closed-loop control system. Our system has linear dynamic in state transition, and a nonlinear mapping from the state to the measurement. An iterative extended Kalman filter (IEKF) is shown to accurately predict the unknown states, and nonlinear observability is discussed. Linear-quadratic regulator (LQR) is applied to correct the misalignments. The method is validated experimentally on the optical bench with a commercial OAP. We conduct 100 tests in the experiment to demonstrate the consistency in between runs.

Detecting higher-order wavefront errors with an astigmatic hybrid wavefront sensor.

PubMed

Barwick, Shane

2009-06-01

The reconstruction of wavefront errors from measurements over subapertures can be made more accurate if a fully characterized quadratic surface can be fitted to the local wavefront surface. An astigmatic hybrid wavefront sensor with added neural network postprocessing is shown to have this capability, provided that the focal image of each subaperture is sufficiently sampled. Furthermore, complete local curvature information is obtained with a single image without splitting beam power.

Study of an instrument for sensing errors in a telescope wavefront

NASA Technical Reports Server (NTRS)

Golden, L. J.; Shack, R. V.; Slater, P. N.

1974-01-01

Focal plane sensors for determining the error in a telescope wavefront were investigated. The construction of three candidate test instruments and their evaluation in terms of small wavefront error aberration measurements are described. A laboratory wavefront simulator was designed and fabricated to evaluate the test instruments. The laboratory wavefront error simulator was used to evaluate three tests; a Hartmann test, a polarization shearing interferometer test, and an interferometric Zernike test.

Performance of the Keck Observatory adaptive-optics system.

PubMed

van Dam, Marcos A; Le Mignant, David; Macintosh, Bruce A

2004-10-10

The adaptive-optics (AO) system at the W. M. Keck Observatory is characterized. We calculate the error budget of the Keck AO system operating in natural guide star mode with a near-infrared imaging camera. The measurement noise and bandwidth errors are obtained by modeling the control loops and recording residual centroids. Results of sky performance tests are presented: The AO system is shown to deliver images with average Strehl ratios of as much as 0.37 at 1.58 microm when a bright guide star is used and of 0.19 for a magnitude 12 star. The images are consistent with the predicted wave-front error based on our error budget estimates.

Experimental demonstration of in-plane negative-angle refraction with an array of silicon nanoposts.

PubMed

Wu, Aimin; Li, Hao; Du, Junjie; Ni, Xingjie; Ye, Ziliang; Wang, Yuan; Sheng, Zhen; Zou, Shichang; Gan, Fuwan; Zhang, Xiang; Wang, Xi

2015-03-11

Controlling an optical beam is fundamental in optics. Recently, unique manipulation of optical wavefronts has been successfully demonstrated by metasurfaces. However, these artificially engineered nanostructures have thus far been limited to operate on light beams propagating out-of-plane. The in-plane operation is critical for on-chip photonic applications. Here, we demonstrate an anomalous negative-angle refraction of a light beam propagating along the plane, by designing a thin dielectric array of silicon nanoposts. The circularly polarized dipoles induced by the high-permittivity nanoposts at the scattering resonance significantly shape the wavefront of the light beam and bend it anomalously. The unique capability of a thin line of the nanoposts for manipulating in-plane wavefronts makes the device extremely compact. The low loss all-dielectric structure is compatible with complementary metal-oxide semiconductor technologies, offering an effective solution for in-plane beam steering and routing for on-chip photonics.

Curvature wavefront sensing performance evaluation for active correction of the Large Synoptic Survey Telescope (LSST).

PubMed

Manuel, Anastacia M; Phillion, Donald W; Olivier, Scot S; Baker, Kevin L; Cannon, Brice

2010-01-18

The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary, along with three refractive corrector lenses to produce a flat focal plane with a field of view of 9.6 square degrees. In order to maintain image quality during operation, the deformations and rigid body motions of the three large mirrors must be actively controlled to minimize optical aberrations, which arise primarily from forces due to gravity and thermal expansion. We describe the methodology for measuring the telescope aberrations using a set of curvature wavefront sensors located in the four corners of the LSST camera focal plane. We present a comprehensive analysis of the wavefront sensing system, including the availability of reference stars, demonstrating that this system will perform to the specifications required to meet the LSST performance goals.

Atmospheric turbulence temperature on the laser wavefront properties

NASA Astrophysics Data System (ADS)

Contreras López, J. C.; Ballesteros Díaz, A.; Tíjaro Rojas, O. J.; Torres Moreno, Y.

2017-06-01

Temperature is a physical magnitude that if is higher, the refractive index presents more important random fluctuations, which produce a greater distortion in the wavefront and thus a displacement in its centroid. To observe the effect produced by the turbulent medium strongly influenced by temperature on propagation laser beam, we experimented with two variable and controllable temperature systems designed as optical turbulence generators (OTG): a Turbulator and a Parallelepiped glass container. The experimental setup use three CMOS cameras and four temperature sensors spatially distributed to acquire synchronously information of the laser beam wavefront and turbulence temperature, respectively. The acquired information was analyzed with MATLAB® software tool, that it allows to compute the position, in terms of the evolution time, of the laser beam center of mass and their deviations produced by different turbulent conditions generated inside the two manufactured systems. The results were reflected in the statistical analysis of the centroid shifting.

Broadband acoustic phased array with subwavelength active tube array

NASA Astrophysics Data System (ADS)

Li, Xiao-Yan; Yang, Zhang-Zhao; Zhu, Yi-Fan; Zou, Xin-Ye; Cheng, Jian-Chun

2018-02-01

Acoustic metasurfaces provide a way to manipulate wavefronts at anomalous reflection or refraction angles through subwavelength structures. Here, based on the generalized Snell's refraction law for acoustic metasurfaces and the classical acoustic phased array (PA) theory, a broadband acoustic PA with a subwavelength active tube array has been proposed to form a special acoustic beam and to determine the directivity characteristics of the acoustic source. Theoretical analysis shows that the dispersionless wavefront manipulation can be realized by the gradient model of the active tube array, and a wide working frequency band can be obtained in practical applications from the simulated and experimental results. The numerical results of forming a special acoustic beam and establishing an acoustic focus model with an arbitrary focal position are consistent with the theoretical predictions. The experimental results agree well with the simulated results in the model of forming the acoustic beam of 45 ° . By combining acoustic metamaterials and conventional acoustic PA, the model of the active tube array paves a way to design a composite acoustic PA with high radiation efficiency and system robustness without the need for any complex circuit control system. This design concept is expected to be used in the design of ultrasonic therapy devices and high-efficiency transducers.

Laser Beam Steering/shaping for Free Space Optical Communication

NASA Technical Reports Server (NTRS)

Wang, Xinghua; Wang, Bin; Bos, Philip J.; Anderson, James E.; Pouch, John; Miranda, Felix; McManamon, Paul F.

2004-01-01

The 2-D Optical Phased Array (OPA) antenna based on a Liquid Crystal On Silicon (LCoS) device can be considered for use in free space optical communication as an active beam controlling device. Several examples of the functionality of the device include: beam steering in the horizontal and elevation direction; high resolution wavefront compensation in a large telescope; and beam shaping with the computer generated kinoform. Various issues related to the diffraction efficiency, steering range, steering accuracy as well as the magnitude of wavefront compensation are discussed.

Sensing more modes with fewer sub-apertures: the LIFTed Shack-Hartmann wavefront sensor.

PubMed

Meimon, Serge; Fusco, Thierry; Michau, Vincent; Plantet, Cédric

2014-05-15

We propose here a novel way to analyze Shack-Hartmann wavefront sensor images in order to retrieve more modes than the two centroid coordinates per sub-aperture. To do so, we use the linearized focal-plane technique (LIFT) phase retrieval method for each sub-aperture. We demonstrate that we can increase the number of modes sensed with the same computational burden per mode. For instance, we show the ability to control a 21×21 actuator deformable mirror using a 10×10 lenslet array.

Simulation of electrowetting lens and prism arrays for wavefront compensation.

PubMed

Gopinath, Juliet T; Bright, Victor M; Cogswell, Carol C; Niederriter, Robert D; Watson, Alexander; Zahreddine, Ramzi; Cormack, Robert H

2012-09-20

A novel application of electrowetting devices has been simulated: wavefront correction using an array of electrowetting lenses and prisms. Five waves of distortion can be corrected with Strehl ratios of 0.9 or higher, utilizing piston, tip-tilt, and curvature corrections from arrays of 19 elements and fill factors as low as 40%. Effective control of piston can be achieved by placing the liquid lens array at the focus of two microlens arrays. Seven waves of piston delay can be generated with variation in focal length between 1.5 and 500 mm.

Adaptive optics system for the IRSOL solar observatory

NASA Astrophysics Data System (ADS)

Ramelli, Renzo; Bucher, Roberto; Rossini, Leopoldo; Bianda, Michele; Balemi, Silvano

2010-07-01

We present a low cost adaptive optics system developed for the solar observatory at Istituto Ricerche Solari Locarno (IRSOL), Switzerland. The Shack-Hartmann Wavefront Sensor is based on a Dalsa CCD camera with 256 pixels × 256 pixels working at 1kHz. The wavefront compensation is obtained by a deformable mirror with 37 actuators and a Tip-Tilt mirror. A real time control software has been developed on a RTAI-Linux PC. Scicos/Scilab based software has been realized for an online analysis of the system behavior. The software is completely open source.

Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO

NASA Astrophysics Data System (ADS)

N'Diaye, M.; Martinache, F.; Jovanovic, N.; Lozi, J.; Guyon, O.; Norris, B.; Ceau, A.; Mary, D.

2018-02-01

Context. Island effect (IE) aberrations are induced by differential pistons, tips, and tilts between neighboring pupil segments on ground-based telescopes, which severely limit the observations of circumstellar environments on the recently deployed exoplanet imagers (e.g., VLT/SPHERE, Gemini/GPI, Subaru/SCExAO) during the best observing conditions. Caused by air temperature gradients at the level of the telescope spiders, these aberrations were recently diagnosed with success on VLT/SPHERE, but so far no complete calibration has been performed to overcome this issue. Aims: We propose closed-loop focal plane wavefront control based on the asymmetric Fourier pupil wavefront sensor (APF-WFS) to calibrate these aberrations and improve the image quality of exoplanet high-contrast instruments in the presence of the IE. Methods: Assuming the archetypal four-quadrant aperture geometry in 8 m class telescopes, we describe these aberrations as a sum of the independent modes of piston, tip, and tilt that are distributed in each quadrant of the telescope pupil. We calibrate these modes with the APF-WFS before introducing our wavefront control for closed-loop operation. We perform numerical simulations and then experimental tests on a real system using Subaru/SCExAO to validate our control loop in the laboratory and on-sky. Results: Closed-loop operation with the APF-WFS enables the compensation for the IE in simulations and in the laboratory for the small aberration regime. Based on a calibration in the near infrared, we observe an improvement of the image quality in the visible range on the SCExAO/VAMPIRES module with a relative increase in the image Strehl ratio of 37%. Conclusions: Our first IE calibration paves the way for maximizing the science operations of the current exoplanet imagers. Such an approach and its results prove also very promising in light of the Extremely Large Telescopes (ELTs) and the presence of similar artifacts with their complex aperture geometry.

Hybrid wavefront sensor for the fast detection of wavefront disturbances.

PubMed

Dong, Shihao; Haist, Tobias; Osten, Wolfgang

2012-09-01

Strongly aberrated wavefronts lead to inaccuracies and nonlinearities in holography-based modal wavefront sensing (HMWS). In this contribution, a low-resolution Shack-Hartmann sensor (LRSHS) is incorporated into HMWS via a compact holographic design to extend the dynamic range of HMWS. A static binary-phase computer-generated hologram is employed to generate the desired patterns for Shack-Hartmann sensing and HMWS. The low-order aberration modes dominating the wavefront error are first sensed with the LRSHS and corrected by the wavefront modulator. The system then switches to HMWS to obtain better sensor sensitivity and accuracy. Simulated as well as experimental results are shown for validating the proposed method.

JWST testbed telescope: a functionally accurate scaled version of the flight optical telescope element used to develop the flight wavefront sensing and control algorithm

NASA Astrophysics Data System (ADS)

Kingsbury, Lana K.; Atcheson, Paul D.

2004-10-01

The Northrop-Grumman/Ball/Kodak team is building the JWST observatory that will be launched in 2011. To develop the flight wavefront sensing and control (WFS&C) algorithms and software, Ball is designing and building a 1 meter diameter, functionally accurate version of the JWST optical telescope element (OTE). This testbed telescope (TBT) will incorporate the same optical element control capability as the flight OTE. The secondary mirror will be controlled by a 6 degree of freedom (dof) hexapod and each of the 18 segmented primary mirror assemblies will have 6 dof hexapod control as well as radius of curvature adjustment capability. In addition to the highly adjustable primary and secondary mirrors, the TBT will include a rigid tertiary mirror, 2 fold mirrors (to direct light into the TBT) and a very stable supporting structure. The total telescope system configured residual wavefront error will be better than 175 nm RMS double pass. The primary and secondary mirror hexapod assemblies enable 5 nm piston resolution, 0.0014 arcsec tilt resolution, 100 nm translation resolution, and 0.04497 arcsec clocking resolution. The supporting structure (specifically the secondary mirror support structure) is designed to ensure that the primary mirror segments will not change their despace position relative to the secondary mirror (spaced > 1 meter apart) by greater than 500 nm within a one hour period of ambient clean room operation.

Determination of wavefront structure for a Hartmann wavefront sensor using a phase-retrieval method.

PubMed

Polo, A; Kutchoukov, V; Bociort, F; Pereira, S F; Urbach, H P

2012-03-26

We apply a phase retrieval algorithm to the intensity pattern of a Hartmann wavefront sensor to measure with enhanced accuracy the phase structure of a Hartmann hole array. It is shown that the rms wavefront error achieved by phase reconstruction is one order of magnitude smaller than the one obtained from a typical centroid algorithm. Experimental results are consistent with a phase measurement performed independently using a Shack-Hartmann wavefront sensor.

Spectrally resolved single-shot wavefront sensing of broadband high-harmonic sources

NASA Astrophysics Data System (ADS)

Freisem, L.; Jansen, G. S. M.; Rudolf, D.; Eikema, K. S. E.; Witte, S.

2018-03-01

Wavefront sensors are an important tool to characterize coherent beams of extreme ultraviolet radiation. However, conventional Hartmann-type sensors do not allow for independent wavefront characterization of different spectral components that may be present in a beam, which limits their applicability for intrinsically broadband high-harmonic generation (HHG) sources. Here we introduce a wavefront sensor that measures the wavefronts of all the harmonics in a HHG beam in a single camera exposure. By replacing the mask apertures with transmission gratings at different orientations, we simultaneously detect harmonic wavefronts and spectra, and obtain sensitivity to spatiotemporal structure such as pulse front tilt as well. We demonstrate the capabilities of the sensor through a parallel measurement of the wavefronts of 9 harmonics in a wavelength range between 25 and 49 nm, with up to lambda/32 precision.

Estimate Low and High Order Wavefront Using P1640 Calibrator Measurements

NASA Technical Reports Server (NTRS)

Zhai, C.; Vasisht, G.; Shao, M.; Lockhart, T.; Cady, E.; Oppenheimer, B.; Burruss, R.; Roberts, J.; Beichman, C.; Brenner, D.;

Two-years results of small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis for Myopia.

PubMed

Kobashi, Hidenaga; Kamiya, Kazutaka; Igarashi, Akihito; Takahashi, Masahide; Shimizu, Kimiya

2018-03-01

To compare the 2-years visual and refractive outcomes between small-incision lenticule extraction (SMILE) and wavefront-guided laser in situ keratomileusis (LASIK) in eyes with myopia and myopic astigmatism. Our retrospective case-control study examined 30 eyes of 30 patients with the manifest refraction spherical equivalent (MRSE) of -3.71 ± 1.83 dioptres (D) who underwent SMILE and 30 eyes of 30 patients with MRSE of -3.81 ± 1.40 D who underwent wavefront-guided LASIK. We assessed the 2-years clinical outcomes. Logarithm of the minimal angle of resolution (LogMAR)-corrected distance visual acuity (CDVA) was -0.23 ± 0.07 in the SMILE group and -0.24 ± 0.07 in the wavefront-guided LASIK group 2 years postoperatively (p = 0.82). Logarithm of the minimal angle of resolution-uncorrected distance visual acuity (UDVA) was -0.18 ± 0.09 and -0.15 ± 0.11 (p = 0.30, respectively). In the SMILE and wavefront-guided LASIK groups 2 years postoperatively, 100% and 73% of eyes, respectively, were within 0.5 D of the prompted MRSE correction (p = 0.005). Changes in the MRSE of -0.10 ± 0.30 D and -0.23 ± 0.51 D occurred from 3 months to 2 years (p = 0.40, respectively). We found a significant correlation between myopic regression and the changes in the keratometric readings from 3 months to 2 years after wavefront-guided LASIK (r = -0.48, p = 0.002), but not after SMILE (r = -0.004, p = 0.90). Small-incision lenticule extraction offers better refractive outcomes than wavefront-guided LASIK during a 2-years follow-up for the correction of myopia and myopic astigmatism. © 2017 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

Adaptive Optics for Industry and Medicine

NASA Astrophysics Data System (ADS)

Dainty, Christopher

2008-01-01

pt. 1. Wavefront correctors and control. Liquid crystal lenses for correction of presbyopia (Invited Paper) / Guoqiang Li and Nasser Peyghambarian. Converging and diverging liquid crystal lenses (oral paper) / Andrew X. Kirby, Philip J. W. Hands, and Gordon D. Love. Liquid lens technology for miniature imaging systems: status of the technology, performance of existing products and future trends (invited paper) / Bruno Berge. Carbon fiber reinforced polymer deformable mirrors for high energy laser applications (oral paper) / S. R. Restaino ... [et al.]. Tiny multilayer deformable mirrors (oral paper) / Tatiana Cherezova ... [et al.]. Performance analysis of piezoelectric deformable mirrors (oral paper) / Oleg Soloviev, Mikhail Loktev and Gleb Vdovin. Deformable membrane mirror with high actuator density and distributed control (oral paper) / Roger Hamelinck ... [et al.]. Characterization and closed-loop demonstration of a novel electrostatic membrane mirror using COTS membranes (oral paper) / David Dayton ... [et al.]. Electrostatic micro-deformable mirror based on polymer materials (oral paper) / Frederic Zamkotsian ... [et al.]. Recent progress in CMOS integrated MEMS A0 mirror development (oral paper) / A. Gehner ... [et al.]. Compact large-stroke piston-tip-tilt actuator and mirror (oral paper) / W. Noell ... [et al.]. MEMS deformable mirrors for high performance AO applications (oral paper) / Paul Bierden, Thomas Bifano and Steven Cornelissen. A versatile interferometric test-rig for the investigation and evaluation of ophthalmic AO systems (poster paper) / Steve Gruppetta, Jiang Jian Zhong and Luis Diaz-Santana. Woofer-tweeter adaptive optics (poster paper) / Thomas Farrell and Chris Dainty. Deformable mirrors based on transversal piezoeffect (poster paper) / Gleb Vdovin, Mikhail Loktev and Oleg Soloviev. Low-cost spatial light modulators for ophthalmic applications (poster paper) / Vincente Durán ... [et al.]. Latest MEMS DM developments and the path ahead at Iris AO (poster paper) / Michael A. Helmbrecht ... [et al.]. Electrostatic push pull mirror improvernents in visual optics (poster paper) / S. Bonora and L. Poletto. 25cm bimorph mirror for petawatt laser / S. Bonora ... [et al.]. Hysteresis compensation for piezo deformable mirror (poster paper) / H. Song ... [et al.]. Static and dynamic responses of an adaptive optics ferrofluidic mirror (poster paper) / A. Seaman ... [et al.]. New HDTV (1920 x 1080) phase-only SLM (poster paper) / Stefan Osten and Sven Krueger. Monomorph large aperture deformable mirror for laser applications (poster paper) / J-C Sinquin, J-M Lurcon, C. Guillemard. Low cost, high speed for adaptive optics control (oral paper) / Christopher D. Saunter and Gordon D. Love. Open loop woofer-tweeter adaptive control on the LAO multi-conjugate adaptive optics testbed (oral paper) / Edward Laag, Don Gavel and Mark Ammons -- pt. 2. Wavefront sensors. Wave front sensorless adaptive optics for imaging and microscopy (invited paper) / Martin J. Booth, Delphine Débarre and Tony Wilson. A fundamental limit for wavefront sensing (oral paper) / Carl Paterson. Coherent fibre-bundle wavefront sensor (oral paper) / Brian Vohnsen, I. Iglesias and Pablo Artal. Maximum-likelihood methods in wave-front sensing: nuisance parameters (oral paper) / David Lara, Harrison H. Barrett, and Chris Dainty. Real-time wavefront sensing for ultrafast high-power laser beams (oral paper) / Juan M. Bueno ... [et al.]. Wavefront sensing using a random phase screen (oral paper) / M. Loktev, G. Vdovin and O. Soloviev. Quadri-Wave Lateral Shearing Interferometry: a new mature technique for wave front sensing in adaptive optics (oral paper) / Benoit Wattellier ... [et al.]. In vivo measurement of ocular aberrations with a distorted grating wavefront sensor (oral paper) / P. Harrison ... [et al.]. Position-sensitive detector designed with unusual CMOS layout strategies for a Hartman-Shack wavefront sensor (oral Paper) / Davies W. de Lima Monteiro ... [et al.]. Adaptive optics system to compensate complex-shaped wavefronts (oral paper) / Miguel Ares, and Santiago Royo. A kind of novel linear phase retrieval wavefront sensor and its application in close-loop adaptive optics system (oral paper) / Xinyang Li ... [et al.]. Ophthalmic Shack-Hatmann wavefront sensor applications (oral paper) / Daniel R. Neal. Wave front sensing of an optical vortex and its correction with the help of bimorph mirror (poster paper) / F. A. Starikov ... [et al.]. Recent advances in laser metrology and correction of high numerical aperture laser beams using quadri-wave lateral shearing-interferometry (poster paper) / Benoit Wattellier, Ivan Doudet and William Boucher. Thin film optical metrology using principles of wavefront sensing and interference (poster paper) / D. M. Faichnie, A. H. Greenaway and I. Bain. Direct diffractive image simulation (poster paper) / A. P. Maryasov, N. P. Maryasov, A. P. Layko. High speed smart CMOS sensor for adaptive optics (poster paper) / T. D. Raymond ... [et al.]. Traceable astigmatism measurements for wavefront sensors (poster paper) / S. R. G. Hall, S. D. Knox, R. F. Stevens -- pt. 3. Adaptive optics in vision science. Dual-conjugate adaptive optics instrument for wide-field retinal imaging (oral paper) / Jörgen Thaung, Mette-Owner Petersen and Zoran Popovic. Visual simulation using electromagnetic adaptive-optics (oral paper) / Laurent Vabre ... [et al.]. High-resolution field-of-view widening in human eye retina imaging (oral paper) / Alexander V. Dubinin, Tatyana Yu. Cherezova, Alexis V. Kudryashov. Psychophysical experiments on visual performance with an ocular adaptive optics system (oral paper) / E. Dalimier, J. C. Dainty and J. Barbur. Does the accommodative mechanism of the eye calibrate itself using aberration dynamics? (oral paper) / K. M. Hampson, S. S. Chin and E. A. H. Mallen. A study of field aberrations in the human eye (oral paper) / Alexander V. Goncharov ... [et al.]. Dual wavefront corrector ophthalmic adaptive optics: design and alignment (oral paper) / Alfredo Dubra and David Williams. High speed simultaneous SLO/OCT imaging of the human retina with adaptive optics (oral paper) / M. Pircher ... [et al.]. Characterization of an AO-OCT system (oral paper) / Julia W. Evans ... [et al.]. Adaptive optics optical coherence tomography for retina imaging (oral paper) / Guohua Shi ... [et al.]. Development, calibration and performance of an electromagnetic-mirror-based adaptive optics system for visual optics (oral paper) / Enrique Gambra ... [et al.]. Adaptive eye model (poster paper) / Sergey O. Galetskzy and Alexty V. Kudryashov. Adaptive optics system for retinal imaging based on a pyramid wavefront sensor (poster paper) / Sabine Chiesa ... [et al.]. Modeling of non-stationary dynamic ocular aberrations (poster paper) / Conor Leahy and Chris Dainty. High-order aberrations and accommodation of human eye (poster paper) / Lixia Xue ... [et al.]. Electromagnetic deformable mirror: experimental assessment and first ophthalmic applications (poster paper) / L. Vabre ... [et al.]. Correcting ocular aberrations in optical coherence tomography (poster paper) / Simon Tuohy ... [et al.] -- pt. 4. Adaptive optics in optical storage and microscopy. The application of liquid crystal aberration compensator for the optical disc systems (invited paper) / Masakazu Ogasawara. Commercialization of the adaptive scanning optical microscope (ASOM) (oral paper) / Benjamin Potsaid ... [et al.]. A practical implementation of adaptive optics for aberration compensation in optical microscopy (oral paper) / A. J. Wright ... [et al.]. Active focus locking in an optically sectioning microscope using adaptive optics (poster paper) / S. Poland, A. J. Wright, J. M. Girkin. Towards four dimensional particle tracking for biological applications / Heather I. Campbell ... [et al.]. Adaptive optics for microscopy (poster paper) / Xavier Levecq -- pt. 5. Adaptive optics in lasers. Improved beam quality of a high power Yb: YAG laser (oral paper) / Dennis G. Harris ... [et al.]. Intracavity adaptive optics optimization of an end-pumped Nd:YVO4 laser (oral paper) / Petra Welp, Ulrich Wittrock. New results in high power lasers beam correction (oral paper) / Alexis Kudryashov ... [et al.]. Adaptive optical systems for the Shenguang-III prototype facility (oral paper) / Zeping Yang ... [et al.]. Adaptive optics control of solid-state lasers (poster paper) / Walter Lubeigt ... [et al.]. Gerchberg-Saxton algorithm for multimode beam reshaping (poster paper) / Inna V. Ilyina, Tatyana Yu. Cherezova. New algorithm of combining for spatial coherent beams (poster paper) / Ruofu Yang ... [et al.]. Intracavity mode control of a solid-state laser using a 19-element deformable mirror (poster paper) / Ping Yang ... [et al.] -- pt. 6. Adaptive optics in communication and atmospheric compensation. Fourier image sharpness sensor for laser communications (oral paper) / Kristin N. Walker and Robert K. Tyson. Fast closed-loop adaptive optics system for imaging through strong turbulence layers (oral paper) / Ivo Buske and Wolfgang Riede. Correction of wavefront aberrations and optical communication using aperture synthesis (oral paper) / R. J. Eastwood ... [et al.]. Adaptive optics system for a small telescope (oral paper) / G. Vdovin, M. Loktev and O. Soloviev. Fast correction of atmospheric turbulence using a membrane deformable mirror (poster paper) / Ivan Capraro, Stefano Bonora, Paolo Villoresi. Atmospheric turbulence measurements over a 3km horizontal path with a Shack-Hartmann wavefront sensor (poster paper) / Ruth Mackey, K. Murphy and Chris Dainty. Field-oriented wavefront sensor for laser guide stars (poster paper) / Lidija Bolbasova, Alexander Goncharov and Vladimir Lukin.

Stitching of near-nulled subaperture measurements

NASA Technical Reports Server (NTRS)

Devries, Gary (Inventor); Brophy, Christopher (Inventor); Forbes, Greg (Inventor); Murphy, Paul (Inventor)

2012-01-01

A metrology system for measuring aspheric test objects by subaperture stitching. A wavefront-measuring gauge having a limited capture range of wavefront shapes collects partially overlapping subaperture measurements over the test object. A variable optical aberrator reshapes the measurement wavefront with between a limited number of the measurements to maintain the measurement wavefront within the capture range of the wavefront-measuring gauge. Various error compensators are incorporated into a stitching operation to manage residual errors associated with the use of the variable optical aberrator.

The plenoptic camera as a wavefront sensor for the European Solar Telescope (EST)

NASA Astrophysics Data System (ADS)

Rodríguez-Ramos, Luis F.; Martín, Yolanda; Díaz, José J.; Piqueras, J.; Rodríguez-Ramos, J. M.

2009-08-01

The plenoptic wavefront sensor combines measurements at pupil and image planes in order to obtain wavefront information from different points of view simultaneously, being capable to sample the volume above the telescope to extract the tomographic information of the atmospheric turbulence. After describing the working principle, a laboratory setup has been used for the verification of the capability of measuring the pupil plane wavefront. A comparative discussion with respect to other wavefront sensors is also included.

Thermally induced distortion of high average power laser system by an optical transport system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ault, L; Chow, R; Taylor, Jedlovec, D

1999-03-31

The atomic vapor laser isotope separation process uses high-average power lasers that have the commercial potential to enrich uranium for the electric power utilities. The transport of the laser beam through the laser system to the separation chambers requires high performance optical components, most of which have either fused silica or Zerodur as the substrate material. One of the requirements of the optical components is to preserve the wavefront quality of the laser beam that propagate over long distances. Full aperture tests with the high power process lasers and finite element analysis (FEA) have been performed on the transport optics.more » The wavefront distortions of the various sections of the transport path were measured with diagnostic Hartmann sensor packages. The FEA results were derived from an in-house thermal-structural-optical code which is linked to the commercially available CodeV program. In comparing the measured and predicted results, the bulk absorptance of fused silica was estimated to about 50 ppm/cm in the visible wavelength regime. Wavefront distortions are reported on optics made from fused silica and Zerodur substrate materials.« less

Wavefront sensing with a thin diffuser

NASA Astrophysics Data System (ADS)

Berto, Pascal; Rigneault, Hervé; Guillon, Marc

2017-12-01

We propose and implement a broadband, compact, and low-cost wavefront sensing scheme by simply placing a thin diffuser in the close vicinity of a camera. The local wavefront gradient is determined from the local translation of the speckle pattern. The translation vector map is computed thanks to a fast diffeomorphic image registration algorithm and integrated to reconstruct the wavefront profile. The simple translation of speckle grains under local wavefront tip/tilt is ensured by the so-called "memory effect" of the diffuser. Quantitative wavefront measurements are experimentally demonstrated both for the few first Zernike polynomials and for phase-imaging applications requiring high resolution. We finally provided a theoretical description of the resolution limit that is supported experimentally.

Fast algorithm for wavefront reconstruction in XAO/SCAO with pyramid wavefront sensor

NASA Astrophysics Data System (ADS)

Shatokhina, Iuliia; Obereder, Andreas; Ramlau, Ronny

2014-08-01

We present a fast wavefront reconstruction algorithm developed for an extreme adaptive optics system equipped with a pyramid wavefront sensor on a 42m telescope. The method is called the Preprocessed Cumulative Reconstructor with domain decomposition (P-CuReD). The algorithm is based on the theoretical relationship between pyramid and Shack-Hartmann wavefront sensor data. The algorithm consists of two consecutive steps - a data preprocessing, and an application of the CuReD algorithm, which is a fast method for wavefront reconstruction from Shack-Hartmann sensor data. The closed loop simulation results show that the P-CuReD method provides the same reconstruction quality and is significantly faster than an MVM.

The SCHWIND AMARIS Total-Tech Laser as An All-Rounder in Refractive Surgery

PubMed Central

Arbelaez, Maria Clara; Mosquera, Samuel Arba

2009-01-01

Purpose: To describe and argument an overview of the main features and unique technical points of AMARIS Total-Tech Laser, coupled with patient outcomes supporting the decision to perform LASIK treatments with maximised outcomes. Settings: Dr. M.C. Arbelaez, Muscat Eye Laser Center, Muscat, Sultanate of Oman. Methods: The findings collected during 18-month experience using SCHWIND AMARIS Total-Tech Laser have been reviewed to provide arguments for supporting the decision to perform LASIK treatments with maximised outcomes. For updated clinical outcomes, the last 100 myopic astigmatism treatments, the last 100 hyperopic astigmatism treatments, the last 30 ocular-wavefront-guided treatments, and the last 30 corneal-wavefront-guided treatments, all with 6-month follow-up, were included. For all those, LDV femtosecond system was used to prepare the flaps, and AMARIS flying spot system was used to perform ablations. Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, wavefront aberration, and contrast sensitivity. Results: 6-month postoperatively, mean defocus was −0.14±0.31D and astigmatism 0.25±0.37D. 70± eyes were within ±0.25D of emmetropia. 43± eyes gained lines of best spectacle-corrected visual acuity. For Aberration-Free treatments, none of the aberration metrics changed from pre- to postoperative values in a clinically relevant amount. For ocular-wavefront-guided treatments, the surgery did not change coma or spherical aberration, and reduced trefoil (p<0.005). For corneal-wavefront-guided treatments, the trefoil, coma, and spherical aberrations, as well as the total root-mean-square values of higher order aberration, were significantly reduced (p<.05) when the pre-existing aberrations were greater than the repeatability and the biological noise. Conclusions: Although this review does not allow for evidence-based conclusions, following our strategy, LASIK results were excellent. LASIK surgery with AMARIS system yield excellent outcomes. Refractions were reduced to subclinical values with no induction of High-Order-Aberrations. Neither adverse events nor complications were observed. PMID:20142960

JWST Wavefront Control Toolbox

NASA Technical Reports Server (NTRS)

Shin, Shahram Ron; Aronstein, David L.

2011-01-01

A Matlab-based toolbox has been developed for the wavefront control and optimization of segmented optical surfaces to correct for possible misalignments of James Webb Space Telescope (JWST) using influence functions. The toolbox employs both iterative and non-iterative methods to converge to an optimal solution by minimizing the cost function. The toolbox could be used in either of constrained and unconstrained optimizations. The control process involves 1 to 7 degrees-of-freedom perturbations per segment of primary mirror in addition to the 5 degrees of freedom of secondary mirror. The toolbox consists of a series of Matlab/Simulink functions and modules, developed based on a "wrapper" approach, that handles the interface and data flow between existing commercial optical modeling software packages such as Zemax and Code V. The limitations of the algorithm are dictated by the constraints of the moving parts in the mirrors.

The contribution of accommodation and the ocular surface to the microfluctuations of wavefront aberrations of the eye.

PubMed

Zhu, Mingxia; Collins, Michael J; Iskander, D Robert

2006-09-01

We have used videokeratoscopy and wavefront sensing to investigate the contribution of the ocular surface and the effect of stimulus vergence on the microfluctuations of the wavefront aberrations of the eye. The fluctuations of the wavefront aberrations were quantified by their variations around the mean and by using power spectrum analysis. Integrated power was determined in two regions: 0.1-0.7 Hz (low frequencies) and 0.8-1.8 Hz (high frequencies). Changes in the ocular surface topography were measured using high-speed videokeratoscopy and variations in the ocular wavefront aberrations were measured with a wavefront sensor. The microfluctuations of wavefront aberrations of the ocular surface were found to be considerably smaller than the microfluctuations of the wavefront aberrations of the total eye. The fluctuations in defocus while viewing a closer target at 2 or 4 D were found to be significantly greater than fluctuations in defocus when viewing a far target. This increase in defocus fluctuations (p < or = 0.001) occurred in both the low- and high-frequency regions of the power spectra.

Wavefront reconstruction method based on wavelet fractal interpolation for coherent free space optical communication

NASA Astrophysics Data System (ADS)

Zhang, Dai; Hao, Shiqi; Zhao, Qingsong; Zhao, Qi; Wang, Lei; Wan, Xiongfeng

2018-03-01

Existing wavefront reconstruction methods are usually low in resolution, restricted by structure characteristics of the Shack Hartmann wavefront sensor (SH WFS) and the deformable mirror (DM) in the adaptive optics (AO) system, thus, resulting in weak homodyne detection efficiency for free space optical (FSO) communication. In order to solve this problem, we firstly validate the feasibility of liquid crystal spatial light modulator (LC SLM) using in an AO system. Then, wavefront reconstruction method based on wavelet fractal interpolation is proposed after self-similarity analysis of wavefront distortion caused by atmospheric turbulence. Fast wavelet decomposition is operated to multiresolution analyze the wavefront phase spectrum, during which soft threshold denoising is carried out. The resolution of estimated wavefront phase is then improved by fractal interpolation. Finally, fast wavelet reconstruction is taken to recover wavefront phase. Simulation results reflect the superiority of our method in homodyne detection. Compared with minimum variance estimation (MVE) method based on interpolation techniques, the proposed method could obtain superior homodyne detection efficiency with lower operation complexity. Our research findings have theoretical significance in the design of coherent FSO communication system.

Fast autonomous holographic adaptive optics

NASA Astrophysics Data System (ADS)

Andersen, G.

2010-07-01

We have created a new adaptive optics system using a holographic modal wavefront sensing method capable of autonomous (computer-free) closed-loop control of a MEMS deformable mirror. A multiplexed hologram is recorded using the maximum and minimum actuator positions on the deformable mirror as the "modes". On reconstruction, an input beam will be diffracted into pairs of focal spots - the ratio of particular pairs determines the absolute wavefront phase at a particular actuator location. The wavefront measurement is made using a fast, sensitive photo-detector array such as a multi-pixel photon counters. This information is then used to directly control each actuator in the MEMS DM without the need for any computer in the loop. We present initial results of a 32-actuator prototype device. We further demonstrate that being an all-optical, parallel processing scheme, the speed is independent of the number of actuators. In fact, the limitations on speed are ultimately determined by the maximum driving speed of the DM actuators themselves. Finally, being modal in nature, the system is largely insensitive to both obscuration and scintillation. This should make it ideal for laser beam transmission or imaging under highly turbulent conditions.

More Zernike modes' open-loop measurement in the sub-aperture of the Shack-Hartmann wavefront sensor.

PubMed

Zhu, Zhaoyi; Mu, Quanquan; Li, Dayu; Yang, Chengliang; Cao, Zhaoliang; Hu, Lifa; Xuan, Li

2016-10-17

The centroid-based Shack-Hartmann wavefront sensor (SHWFS) treats the sampled wavefronts in the sub-apertures as planes, and the slopes of the sub-wavefronts are used to reconstruct the whole pupil wavefront. The problem is that the centroid method may fail to sense the high-order modes for strong turbulences, decreasing the precision of the whole pupil wavefront reconstruction. To solve this problem, we propose a sub-wavefront estimation method for SHWFS based on the focal plane sensing technique, by which more Zernike modes than the two slopes can be sensed in each sub-aperture. In this paper, the effects on the sub-wavefront estimation method of the related parameters, such as the spot size, the phase offset with its set amplitude and the pixels number in each sub-aperture, are analyzed and these parameters are optimized to achieve high efficiency. After the optimization, open-loop measurement is realized. For the sub-wavefront sensing, we achieve a large linearity range of 3.0 rad RMS for Zernike modes Z2 and Z3, and 2.0 rad RMS for Zernike modes Z4 to Z6 when the pixel number does not exceed 8 × 8 in each sub-aperture. The whole pupil wavefront reconstruction with the modified SHWFS is realized to analyze the improvements brought by the optimized sub-wavefront estimation method. Sixty-five Zernike modes can be reconstructed with a modified SHWFS containing only 7 × 7 sub-apertures, which could reconstruct only 35 modes by the centroid method, and the mean RMS errors of the residual phases are less than 0.2 rad², which is lower than the 0.35 rad² by the centroid method.

Design of the deformable mirror demonstration CubeSat (DeMi)

NASA Astrophysics Data System (ADS)

Douglas, Ewan S.; Allan, Gregory; Barnes, Derek; Figura, Joseph S.; Haughwout, Christian A.; Gubner, Jennifer N.; Knoedler, Alex A.; LeClair, Sarah; Murphy, Thomas J.; Skouloudis, Nikolaos; Merck, John; Opperman, Roedolph A.; Cahoy, Kerri L.

2017-09-01

The Deformable Mirror Demonstration Mission (DeMi) was recently selected by DARPA to demonstrate in-space operation of a wavefront sensor and Microelectromechanical system (MEMS) deformable mirror (DM) payload on a 6U CubeSat. Space telescopes designed to make high-contrast observations using internal coronagraphs for direct characterization of exoplanets require the use of high-actuator density deformable mirrors. These DMs can correct image plane aberrations and speckles caused by imperfections, thermal distortions, and diffraction in the telescope and optics that would otherwise corrupt the wavefront and allow leaking starlight to contaminate coronagraphic images. DeMi is provide on-orbit demonstration and performance characterization of a MEMS deformable mirror and closed loop wavefront sensing. The DeMi payload has two operational modes, one mode that images an internal light source and another mode which uses an external aperture to images stars. Both the internal and external modes include image plane and pupil plane wavefront sensing. The objectives of the internal measurement of the 140-actuator MEMS DM actuator displacement are characterization of the mirror performance and demonstration of closed-loop correction of aberrations in the optical path. Using the external aperture to observe stars of magnitude 2 or brighter, assuming 3-axis stability with less than 0.1 degree of attitude knowledge and jitter below 10 arcsec RMSE, per observation, DeMi will also demonstrate closed loop wavefront control on an astrophysical target. We present an updated payload design, results from simulations and laboratory optical prototyping, as well as present our design for accommodating high-voltage multichannel drive electronics for the DM on a CubeSat.

Target-in-the-loop beam control: basic considerations for analysis and wave-front sensing

NASA Astrophysics Data System (ADS)

Vorontsov, Mikhail A.; Kolosov, Valeriy

2005-01-01

Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related to maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive-index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave). The resulting evolution equation for the MCF is further simplified by use of the smooth-refractive-index approximation. This approximation permits derivation of the transport equation for the return-wave brightness function, analyzed here by the method of characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wave-front sensors that perform sensing of speckle-averaged characteristics of the wave-front phase (TIL sensors). Analysis of the wave-front phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric-turbulence-related phase aberrations. We also show that wave-front sensing results depend on the extended target shape, surface roughness, and outgoing-beam intensity distribution on the target surface. For targets with smooth surfaces and nonflat shapes, the target-induced phase can contain aberrations. The presence of target-induced aberrations in the conjugated phase may result in a deterioration of adaptive system performance.

Target-in-the-loop beam control: basic considerations for analysis and wave-front sensing.

PubMed

Vorontsov, Mikhail A; Kolosov, Valeriy

2005-01-01

Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related to maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive-index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave). The resulting evolution equation for the MCF is further simplified by use of the smooth-refractive-index approximation. This approximation permits derivation of the transport equation for the return-wave brightness function, analyzed here by the method of characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wave-front sensors that perform sensing of speckle-averaged characteristics of the wave-front phase (TIL sensors). Analysis of the wave-front phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric-turbulence-related phase aberrations. We also show that wave-front sensing results depend on the extended target shape, surface roughness, and outgoing-beam intensity distribution on the target surface. For targets with smooth surfaces and nonflat shapes, the target-induced phase can contain aberrations. The presence of target-induced aberrations in the conjugated phase may result in a deterioration of adaptive system performance.

Mid-infrared Shack-Hartmann wavefront sensor fully cryogenic using extended source for endoatmospheric applications.

PubMed

Robert, Clélia; Michau, Vincent; Fleury, Bruno; Magli, Serge; Vial, Laurent

2012-07-02

Adaptive optics provide real-time compensation for atmospheric turbulence. The correction quality relies on a key element: the wavefront sensor. We have designed an adaptive optics system in the mid-infrared range providing high spatial resolution for ground-to-air applications, integrating a Shack-Hartmann infrared wavefront sensor operating on an extended source. This paper describes and justifies the design of the infrared wavefront sensor, while defining and characterizing the Shack-Hartmann wavefront sensor camera. Performance and illustration of field tests are also reported.

Post-Coronagraph Wavefront Sensor for Gemini Planet Imager

NASA Technical Reports Server (NTRS)

Wallace, J. Kent; Burruss, Rick; Pueyo, Laurent; Soummer, Remi; Shelton, Chris; Bartos, Randall; Fregoso, Felipe; Nemati, Bijan; Best, Paul; Angione, John

2009-01-01

The calibration wavefront system for the Gemini Planet Imager (GPI) will measure the complex wavefront at the apodized pupil and provide slow phase errors to the AO system to mitigate against image plane speckles that would cause a loss in contrast. This talk describes both the low-order and high-order sensors in the calibration wavefront sensor and how the information is combined to form the wavefront estimate before the coronagraph. We will show laboratory results from our calibration testbed that demonstrate the subsystem performance at levels commensurate with those required on the final instrument.

A Phase-Shifting Zernike Wavefront Sensor for the Palomar P3K Adaptive Optics System

NASA Technical Reports Server (NTRS)

Wallace, J. Kent; Crawford, Sam; Loya, Frank; Moore, James

2012-01-01

A phase-shifting Zernike wavefront sensor has distinct advantages over other types of wavefront sensors. Chief among them are: 1) improved sensitivity to low-order aberrations and 2) efficient use of photons (hence reduced sensitivity to photon noise). We are in the process of deploying a phase-shifting Zernike wavefront sensor to be used with the realtime adaptive optics system for Palomar. Here we present the current state of the Zernike wavefront sensor to be integrated into the high-order adaptive optics system at Mount Palomar's Hale Telescope.

Predicting crystalline lens fall caused by accommodation from changes in wavefront error

PubMed Central

He, Lin; Applegate, Raymond A.

2011-01-01

PURPOSE To illustrate and develop a method for estimating crystalline lens decentration as a function of accommodative response using changes in wavefront error and show the method and limitations using previously published data (2004) from 2 iridectomized monkey eyes so that clinicians understand how spherical aberration can induce coma, in particular in intraocular lens surgery. SETTINGS College of Optometry, University of Houston, Houston, USA. DESIGN Evaluation of diagnostic test or technology. METHODS Lens decentration was estimated by displacing downward the wavefront error of the lens with respect to the limiting aperture (7.0 mm) and ocular first surface wavefront error for each accommodative response (0.00 to 11.00 diopters) until measured values of vertical coma matched previously published experimental data (2007). Lens decentration was also calculated using an approximation formula that only included spherical aberration and vertical coma. RESULTS The change in calculated vertical coma was consistent with downward lens decentration. Calculated downward lens decentration peaked at approximately 0.48 mm of vertical decentration in the right eye and approximately 0.31 mm of decentration in the left eye using all Zernike modes through the 7th radial order. Calculated lens decentration using only coma and spherical aberration formulas was peaked at approximately 0.45 mm in the right eye and approximately 0.23 mm in the left eye. CONCLUSIONS Lens fall as a function of accommodation was quantified noninvasively using changes in vertical coma driven principally by the accommodation-induced changes in spherical aberration. The newly developed method was valid for a large pupil only. PMID:21700108

Robustness study of the pseudo open-loop controller for multiconjugate adaptive optics.

PubMed

Piatrou, Piotr; Gilles, Luc

2005-02-20

Robustness of the recently proposed "pseudo open-loop control" algorithm against various system errors has been investigated for the representative example of the Gemini-South 8-m telescope multiconjugate adaptive-optics system. The existing model to represent the adaptive-optics system with pseudo open-loop control has been modified to account for misalignments, noise and calibration errors in deformable mirrors, and wave-front sensors. Comparison with the conventional least-squares control model has been done. We show with the aid of both transfer-function pole-placement analysis and Monte Carlo simulations that POLC remains remarkably stable and robust against very large levels of system errors and outperforms in this respect least-squares control. Approximate stability margins as well as performance metrics such as Strehl ratios and rms wave-front residuals averaged over a 1-arc min field of view have been computed for different types and levels of system errors to quantify the expected performance degradation.

Evaluating noise performance of the IUCAA sidecar drive electronics controller (ISDEC) based system for TMT on-instrument wavefront sensing (OIWFS) application

NASA Astrophysics Data System (ADS)

Burse, Mahesh; Chattopadhyay, Sabyasachi; Ramaprakash, A. N.; Sinha, Sakya; Prabhudesai, Swapnil; Punnadi, Sujit; Chordia, Pravin; Kohok, Abhay

2016-07-01

As a part of a design study for the On-Instrument Low Order Wave-front Sensor (OIWFS) for the TMT Infra-Red Imaging Spectrograph (IRIS), we recently evaluated the noise performance of a detector control system consisting of IUCAA SIDECAR DRIVE ELECRONICS CONTROLLER (ISDEC), SIDECAR ASIC and HAWAII-2RG (H2RG) MUX. To understand and improve the performance of this system to serve as a near infrared wavefront sensor, we implemented new read out modes like multiple regions of interest with differential multi-accumulate readout schemes for the HAWAII-2RG (H2RG) detector. In this system, the firmware running in SIDECAR ASIC programs the detector for ROI readout, reads the detector, processes the detector output and writes the digitized data into its internal memory. ISDEC reads the digitized data from ASIC, performs the differential multi-accumulate operations and then sends the processed data to a PC over a USB interface. A special loopback board was designed and used to measure and reduce the noise from SIDECAR ASIC DC biases2. We were able to reduce the mean r.m.s read noise of this system down to 1-2 e. for any arbitrary window frame of 4x4 size at frame rates below about 200 Hz.

Improvement in error propagation in the Shack-Hartmann-type zonal wavefront sensors.

PubMed

Pathak, Biswajit; Boruah, Bosanta R

2017-12-01

Estimation of the wavefront from measured slope values is an essential step in a Shack-Hartmann-type wavefront sensor. Using an appropriate estimation algorithm, these measured slopes are converted into wavefront phase values. Hence, accuracy in wavefront estimation lies in proper interpretation of these measured slope values using the chosen estimation algorithm. There are two important sources of errors associated with the wavefront estimation process, namely, the slope measurement error and the algorithm discretization error. The former type is due to the noise in the slope measurements or to the detector centroiding error, and the latter is a consequence of solving equations of a basic estimation algorithm adopted onto a discrete geometry. These errors deserve particular attention, because they decide the preference of a specific estimation algorithm for wavefront estimation. In this paper, we investigate these two important sources of errors associated with the wavefront estimation algorithms of Shack-Hartmann-type wavefront sensors. We consider the widely used Southwell algorithm and the recently proposed Pathak-Boruah algorithm [J. Opt.16, 055403 (2014)JOOPDB0150-536X10.1088/2040-8978/16/5/055403] and perform a comparative study between the two. We find that the latter algorithm is inherently superior to the Southwell algorithm in terms of the error propagation performance. We also conduct experiments that further establish the correctness of the comparative study between the said two estimation algorithms.

Wavefront propagation from one plane to another with the use of Zernike polynomials and Taylor monomials.

PubMed

Dai, Guang-ming; Campbell, Charles E; Chen, Li; Zhao, Huawei; Chernyak, Dimitri

2009-01-20

In wavefront-driven vision correction, ocular aberrations are often measured on the pupil plane and the correction is applied on a different plane. The problem with this practice is that any changes undergone by the wavefront as it propagates between planes are not currently included in devising customized vision correction. With some valid approximations, we have developed an analytical foundation based on geometric optics in which Zernike polynomials are used to characterize the propagation of the wavefront from one plane to another. Both the boundary and the magnitude of the wavefront change after the propagation. Taylor monomials were used to realize the propagation because of their simple form for this purpose. The method we developed to identify changes in low-order aberrations was verified with the classical vertex correction formula. The method we developed to identify changes in high-order aberrations was verified with ZEMAX ray-tracing software. Although the method may not be valid for highly irregular wavefronts and it was only proven for wavefronts with low-order or high-order aberrations, our analysis showed that changes in the propagating wavefront are significant and should, therefore, be included in calculating vision correction. This new approach could be of major significance in calculating wavefront-driven vision correction whether by refractive surgery, contact lenses, intraocular lenses, or spectacles.

Imaging photorefractive optical vibration measurement method and device

DOEpatents

Telschow, Kenneth L.; Deason, Vance A.; Hale, Thomas C.

2000-01-01

A method and apparatus are disclosed for characterizing a vibrating image of an object of interest. The method includes providing a sensing media having a detection resolution within a limited bandwidth and providing an object of interest having a vibrating medium. Two or more wavefronts are provided, with at least one of the wavefronts being modulated by interacting the one wavefront with the vibrating medium of the object of interest. The another wavefront is modulated such that the difference frequency between the one wavefront and the another wavefront is within a response range of the sensing media. The modulated one wavefront and another wavefront are combined in association with the sensing media to interfere and produce simultaneous vibration measurements that are distributed over the object so as to provide an image of the vibrating medium. The image has an output intensity that is substantially linear with small physical variations within the vibrating medium. Furthermore, the method includes detecting the image. In one implementation, the apparatus comprises a vibration spectrum analyzer having an emitter, a modulator, sensing media and a detector configured so as to realize such method. According to another implementation, the apparatus comprises a vibration imaging device.

Generating Artificial Reference Images for Open Loop Correlation Wavefront Sensors

NASA Astrophysics Data System (ADS)

Townson, M. J.; Love, G. D.; Saunter, C. D.

2018-05-01

Shack-Hartmann wavefront sensors for both solar and laser guide star adaptive optics (with elongated spots) need to observe extended objects. Correlation techniques have been successfully employed to measure the wavefront gradient in solar adaptive optics systems and have been proposed for laser guide star systems. In this paper we describe a method for synthesising reference images for correlation Shack-Hartmann wavefront sensors with a larger field of view than individual sub-apertures. We then show how these supersized reference images can increase the performance of correlation wavefront sensors in regimes where large relative shifts are induced between sub-apertures, such as those observed in open-loop wavefront sensors. The technique we describe requires no external knowledge outside of the wavefront-sensor images, making it available as an entirely "software" upgrade to an existing adaptive optics system. For solar adaptive optics we show the supersized reference images extend the magnitude of shifts which can be accurately measured from 12% to 50% of the field of view of a sub-aperture and in laser guide star wavefront sensors the magnitude of centroids that can be accurately measured is increased from 12% to 25% of the total field of view of the sub-aperture.

Reference-free Shack-Hartmann wavefront sensor.

PubMed

Zhao, Liping; Guo, Wenjiang; Li, Xiang; Chen, I-Ming

2011-08-01

The traditional Shack-Hartmann wavefront sensing (SHWS) system measures the wavefront slope by calculating the centroid shift between the sample and a reference piece, and then the wavefront is reconstructed by a suitable iterative reconstruction method. Because of the necessity of a reference, many issues are brought up, which limit the system in most applications. This Letter proposes a reference-free wavefront sensing (RFWS) methodology, and an RFWS system is built up where wavefront slope changes are measured by introducing a lateral disturbance to the sampling aperture. By using Southwell reconstruction two times to process the measured data, the form of the wavefront at the sampling plane can be well reconstructed. A theoretical simulation platform of RFWS is established, and various surface forms are investigated. Practical measurements with two measurement systems-SHWS and our RFWS-are conducted, analyzed, and compared. All the simulation and measurement results prove and demonstrate the correctness and effectiveness of the method. © 2011 Optical Society of America

Shack-Hartmann wavefront sensing based on binary-aberration-mode filtering.

PubMed

Wang, Shuai; Yang, Ping; Xu, Bing; Dong, Lizhi; Ao, Mingwu

2015-02-23

Spot centroid detection is required by Shack-Hartmann wavefront sensing since the technique was first proposed. For a Shack-Hartmann wavefront sensor, the standard structure is to place a camera behind a lenslet array to record the image of spots. We proposed a new Shack-Hartmann wavefront sensing technique without using spot centroid detection. Based on the principle of binary-aberration-mode filtering, for each subaperture, only one light-detecting unit is used to measure the local wavefront slopes. It is possible to adopt single detectors in Shack-Hartmann wavefront sensor. Thereby, the method is able to gain noise benefits from using singe detectors behind each subaperture when used for sensing rapid varying wavefront in weak light. Moreover, due to non-discrete pixel imaging, this method is a potential solution for high measurement precision with fewer detecting units. Our simulations demonstrate the validity of the theoretical model. In addition, the results also indicate the advantage in measurement accuracy.

Plenoptic camera wavefront sensing with extended sources

NASA Astrophysics Data System (ADS)

Jiang, Pengzhi; Xu, Jieping; Liang, Yonghui; Mao, Hongjun

2016-09-01

The wavefront sensor is used in adaptive optics to detect the atmospheric distortion, which feeds back to the deformable mirror to compensate for this distortion. Different from the Shack-Hartmann sensor that has been widely used with point sources, the plenoptic camera wavefront sensor has been proposed as an alternative wavefront sensor adequate for extended objects in recent years. In this paper, the plenoptic camera wavefront sensing with extended sources is discussed systematically. Simulations are performed to investigate the wavefront measurement error and the closed-loop performance of the plenoptic sensor. The results show that there are an optimal lenslet size and an optimal number of pixels to make the best performance. The RMS of the resulting corrected wavefront in closed-loop adaptive optics system is less than 108 nm (0.2λ) when D/r0 ≤ 10 and the magnitude M ≤ 5. Our investigation indicates that the plenoptic sensor is efficient to operate on extended sources in the closed-loop adaptive optics system.

Novel asymmetric cryptosystem based on distorted wavefront beam illumination and double-random phase encoding.

PubMed

Yu, Honghao; Chang, Jun; Liu, Xin; Wu, Chuhan; He, Yifan; Zhang, Yongjian

2017-04-17

Herein, we propose a new security enhancing method that employs wavefront aberrations as optical keys to improve the resistance capabilities of conventional double-random phase encoding (DRPE) optical cryptosystems. This study has two main innovations. First, we exploit a special beam-expander afocal-reflecting to produce different types of aberrations, and the wavefront distortion can be altered by changing the shape of the afocal-reflecting system using a deformable mirror. Then, we reconstruct the wavefront aberrations via the surface fitting of Zernike polynomials and use the reconstructed aberrations as novel asymmetric vector keys. The ideal wavefront and the distorted wavefront obtained by wavefront sensing can be regarded as a pair of private and public keys. The wavelength and focal length of the Fourier lens can be used as additional keys to increase the number of degrees of freedom. This novel cryptosystem can enhance the resistance to various attacks aimed at DRPE systems. Finally, we conduct ZEMAX and MATLAB simulations to demonstrate the superiority of this method.

Mitotic wavefronts mediated by mechanical signaling in early Drosophila embryos

NASA Astrophysics Data System (ADS)

Kang, Louis; Idema, Timon; Liu, Andrea; Lubensky, Tom

2013-03-01

Mitosis in the early Drosophila embryo demonstrates spatial and temporal correlations in the form of wavefronts that travel across the embryo in each cell cycle. This coordinated phenomenon requires a signaling mechanism, which we suggest is mechanical in origin. We have constructed a theoretical model that supports nonlinear wavefront propagation in a mechanically-excitable medium. Previously, we have shown that this model captures quantitatively the wavefront speed as it varies with cell cycle number, for reasonable values of the elastic moduli and damping coefficient of the medium. Now we show that our model also captures the displacements of cell nuclei in the embryo in response to the traveling wavefront. This new result further supports that mechanical signaling may play an important role in mediating mitotic wavefronts.

Virtual pyramid wavefront sensor for phase unwrapping.

PubMed

Akondi, Vyas; Vohnsen, Brian; Marcos, Susana

2016-10-10

Noise affects wavefront reconstruction from wrapped phase data. A novel method of phase unwrapping is proposed with the help of a virtual pyramid wavefront sensor. The method was tested on noisy wrapped phase images obtained experimentally with a digital phase-shifting point diffraction interferometer. The virtuality of the pyramid wavefront sensor allows easy tuning of the pyramid apex angle and modulation amplitude. It is shown that an optimal modulation amplitude obtained by monitoring the Strehl ratio helps in achieving better accuracy. Through simulation studies and iterative estimation, it is shown that the virtual pyramid wavefront sensor is robust to random noise.

Bottlenecks of the wavefront sensor based on the Talbot effect.

PubMed

Podanchuk, Dmytro; Kovalenko, Andrey; Kurashov, Vitalij; Kotov, Myhaylo; Goloborodko, Andrey; Danko, Volodymyr

2014-04-01

Physical constraints and peculiarities of the wavefront sensing technique, based on the Talbot effect, are discussed. The limitation on the curvature of the measurable wavefront is derived. The requirements to the Fourier spectrum of the periodic mask are formulated. Two kinds of masks are studied for their performance in the wavefront sensor. It is shown that the boundary part of the mask aperture does not contribute to the initial data for wavefront restoration. It is verified by experiment and computer simulation that the performance of the Talbot sensor, which meets established conditions, is similar to that of the Shack-Hartmann sensor.

Simultaneous measurements of density field and wavefront distortions in high speed flows

NASA Astrophysics Data System (ADS)

George, Jacob; Jenkins, Thomas; Trolinger, James; Hess, Cecil; Buckner, Benjamin

2017-09-01

This paper presents results from simultaneous measurements of fluid density and the resulting wavefront distortions in a sonic underexpanded jet. The density measurements were carried out using Rayleigh scattering, and the optical distortions were measured using a wavefront sensor based on phase shifting interferometry. The measurements represent a preliminary step toward relating wavefront distortions to a specific flow structure. The measured density field is used to compute the phase distortions using a wave propagation model based on a geometric-optics approximation, and the computed phase map shows moderate agreement with that obtained using the wavefront sensor.

Optimizing phase to enhance optical trap stiffness.

PubMed

Taylor, Michael A

2017-04-03

Phase optimization offers promising capabilities in optical tweezers, allowing huge increases in the applied forces, trap stiff-ness, or measurement sensitivity. One key obstacle to potential applications is the lack of an efficient algorithm to compute an optimized phase profile, with enhanced trapping experiments relying on slow programs that would take up to a week to converge. Here we introduce an algorithm that reduces the wait from days to minutes. We characterize the achievable in-crease in trap stiffness and its dependence on particle size, refractive index, and optical polarization. We further show that phase-only control can achieve almost all of the enhancement possible with full wavefront shaping; for instance phase control allows 62 times higher trap stiffness for 10 μm silica spheres in water, while amplitude control and non-trivial polarization further increase this by 1.26 and 1.01 respectively. This algorithm will facilitate future applications in optical trapping, and more generally in wavefront optimization.

NASA Tech Briefs, February 2011

NASA Technical Reports Server (NTRS)

2011-01-01

Topics covered include: Multi-Segment Radius Measurement Using an Absolute Distance Meter Through a Null Assembly; Fiber-Optic Magnetic-Field-Strength Measurement System for Lightning Detection; Photocatalytic Active Radiation Measurements and Use; Computer Generated Hologram System for Wavefront Measurement System Calibration; Non-Contact Thermal Properties Measurement with Low-Power Laser and IR Camera System; SpaceCube 2.0: An Advanced Hybrid Onboard Data Processor; CMOS Imager Has Better Cross-Talk and Full-Well Performance; High-Performance Wireless Telemetry; Telemetry-Based Ranging; JWST Wavefront Control Toolbox; Java Image I/O for VICAR, PDS, and ISIS; X-Band Acquisition Aid Software; Antimicrobial-Coated Granules for Disinfecting Water; Range 7 Scanner Integration with PaR Robot Scanning System; Methods of Antimicrobial Coating of Diverse Materials; High-Operating-Temperature Barrier Infrared Detector with Tailorable Cutoff Wavelength; A Model of Reduced Kinetics for Alkane Oxidation Using Constituents and Species for N-Heptane; Thermally Conductive Tape Based on Carbon Nanotube Arrays; Two Catalysts for Selective Oxidation of Contaminant Gases; Nanoscale Metal Oxide Semiconductors for Gas Sensing; Lightweight, Ultra-High-Temperature, CMC-Lined Carbon/Carbon Structures; Sample Acquisition and Handling System from a Remote Platform; Improved Rare-Earth Emitter Hollow Cathode; High-Temperature Smart Structures for Engine Noise Reduction and Performance Enhancement; Cryogenic Scan Mechanism for Fourier Transform Spectrometer; Piezoelectric Rotary Tube Motor; Thermoelectric Energy Conversion Technology for High-Altitude Airships; Combustor Computations for CO2-Neutral Aviation; Use of Dynamic Distortion to Predict and Alleviate Loss of Control; Cycle Time Reduction in Trapped Mercury Ion Atomic Frequency Standards; and A (201)Hg+ Comagnetometer for (199)Hg+ Trapped Ion Space Atomic Clocks.

SU-G-IeP4-09: Method of Human Eye Aberration Measurement Using Plenoptic Camera Over Large Field of View

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lv, Yang; Wang, Ruixing; Ma, Haotong

Purpose: The measurement based on Shack-Hartmann wave-front sensor(WFS), obtaining both the high and low order wave-front aberrations simultaneously and accurately, has been applied in the detection of human eyes aberration in recent years. However, Its application is limited by the small field of view (FOV), slight eye movement leads the optical bacon image exceeds the lenslet array which result in uncertain detection error. To overcome difficulties of precise eye location, the capacity of detecting eye wave-front aberration over FOV much larger than simply a single conjugate Hartmann WFS accurately and simultaneously is demanded. Methods: Plenoptic camera’s lenslet array subdivides themore » aperture light-field in spatial frequency domain, capture the 4-D light-field information. Data recorded by plenoptic cameras can be used to extract the wave-front phases associated to the eyes aberration. The corresponding theoretical model and simulation system is built up in this article to discuss wave-front measurement performance when utilizing plenoptic camera as wave-front sensor. Results: The simulation results indicate that the plenoptic wave-front method can obtain both the high and low order eyes wave-front aberration with the same accuracy as conventional system in single visual angle detectionand over FOV much larger than simply a single conjugate Hartmann systems. Meanwhile, simulation results show that detection of eye aberrations wave-front in different visual angle can be achieved effectively and simultaneously by plenoptic method, by both point and extended optical beacon from the eye. Conclusion: Plenoptic wave-front method possesses the feasibility in eye aberrations wave-front detection. With larger FOV, the method can effectively reduce the detection error brought by imprecise eye location and simplify the eye aberrations wave-front detection system comparing with which based on Shack-Hartmann WFS. Unique advantage of the plenoptic method lies in obtaining wave-front in different visual angle simultaneously, which provides an approach in building up 3-D model of eye refractor tomographically. Funded by the key Laboratory of High Power Laser and Physics, CAS Research Project of National University of Defense Technology No. JC13-07-01; National Natural Science Foundation of China No. 61205144.« less

Optical Quality, Threshold Target Identification, and Military Target Task Performance After Advanced Keratorefractive Surgery

DTIC Science & Technology

2012-05-01

undergo wavefront-guided (WFG) photorefractive keratectomy ( PRK ), WFG laser in situ keratomileusis ( LASIK ), wavefront optimized (WFO) PRK or WFO...Military, Refractive Surgery, PRK , LASIK , Night Vision, Wavefront Optimized, Wavefront Guided, Visual Performance, Quality of Vision, Outcomes...military. In a prospective, randomized treatment trial we will enroll 224 nearsighted soldiers to WFG photorefractive keratectomy ( PRK ), WFG LASIK , WFO PRK

Optical Quality and Threshold Target Identification and Military Target Task Performance after Advanced Keratorefractive Surgery

DTIC Science & Technology

2013-05-01

and Sensors Directorate. • Study participants and physicians select treatment: PRK or LASIK . WFG vs . WFO treatment modality is randomized. The...to undergo wavefront-guided (WFG) photorefractive keratectomy ( PRK ), WFG laser in situ keratomileusis ( LASIK ), wavefront optimized (WFO) PRK or WFO...TERMS Military, Refractive Surgery, PRK , LASIK , Night Vision, Wavefront Optimized, Wavefront Guided, Visual Performance, Quality of Vision, Outcomes

Broadband, Common-path, Interferometric Wavefront Sensor

NASA Technical Reports Server (NTRS)

Wallace, James Kent (Inventor)

2015-01-01

Hybrid sensors comprising Shack-Hartmann Wavefront Sensor (S-HWFS) and Zernike Wavefront Sensor (Z-WFS) capabilities are presented. The hybrid sensor includes a Z-WFS optically arranged in-line with a S-HWFS such that the combined wavefront sensor operates across a wide dynamic range and noise conditions. The Z-WFS may include the ability to introduce a dynamic phase shift in both transmissive and reflective modes.

Horizon: A Proposal for Large Aperture, Active Optics in Geosynchronous Orbit

NASA Technical Reports Server (NTRS)

Chesters, Dennis; Jenstrom, Del

2000-01-01

In 1999, NASA's New Millennium Program called for proposals to validate new technology in high-earth orbit for the Earth Observing-3 (NMP EO3) mission to fly in 2003. In response, we proposed to test a large aperture, active optics telescope in geosynchronous orbit. This would flight-qualify new technologies for both Earth and Space science: 1) a future instrument with LANDSAT image resolution and radiometric quality watching continuously from geosynchronous station, and 2) the Next Generation Space Telescope (NGST) for deep space imaging. Six enabling technologies were to be flight-qualified: 1) a 3-meter, lightweight segmented primary mirror, 2) mirror actuators and mechanisms, 3) a deformable mirror, 4) coarse phasing techniques, 5) phase retrieval for wavefront control during stellar viewing, and 6) phase diversity for wavefront control during Earth viewing. Three enhancing technologies were to be flight- validated: 1) mirror deployment and latching mechanisms, 2) an advanced microcontroller, and 3) GPS at GEO. In particular, two wavefront sensing algorithms, phase retrieval by JPL and phase diversity by ERIM International, were to sense optical system alignment and focus errors, and to correct them using high-precision mirror mechanisms. Active corrections based on Earth scenes are challenging because phase diversity images must be collected from extended, dynamically changing scenes. In addition, an Earth-facing telescope in GEO orbit is subject to a powerful diurnal thermal and radiometric cycle not experienced by deep-space astronomy. The Horizon proposal was a bare-bones design for a lightweight large-aperture, active optical system that is a practical blend of science requirements, emerging technologies, budget constraints, launch vehicle considerations, orbital mechanics, optical hardware, phase-determination algorithms, communication strategy, computational burdens, and first-rate cooperation among earth and space scientists, engineers and managers. This manuscript presents excerpts from the Horizon proposal's sections that describe the Earth science requirements, the structural -thermal-optical design, the wavefront sensing and control, and the on-orbit validation.

SCExAO: the most complete instrument to characterize exoplanets and stellar environments

NASA Astrophysics Data System (ADS)

Lozi, Julien; Guyon, Olivier; Jovanovic, Nemanja; Singh, Garima; Doughty, Danielle; Pathak, Prashant; Goebel, Sean; Kudo, Tomoyuki

2015-12-01

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, currently under development for the Subaru Telescope, optimally combines state-of-the-art technologies to directly study exoplanets and stellar environments at the diffraction limit, both in visible and infrared light (0.6 to 2.4 um). The instrument already includes an ultra-fast visible pyramid wavefront sensor operating at 3.5 kHz, a 2k-actuator deformable mirror, a set of optimal coronagraphs that can work as close as 1 l/D, a low-order wavefront sensor, a high-speed speckle control, and two visible interferometric modules, VAMPIRES and FIRST. Stability of the wavefront correction has already been demonstrated on sky, and SCExAO is already producing scientific results. After the integration of the Integral Field Spectrograph (IFS) CHARIS and a Microwave Kinetic Inductance Detector (MKID) in 2016, SCExAO will be one of the most powerful and effective tools for characterizing exoplanets and disks.

Fast correction approach for wavefront sensorless adaptive optics based on a linear phase diversity technique.

PubMed

Yue, Dan; Nie, Haitao; Li, Ye; Ying, Changsheng

2018-03-01

Wavefront sensorless (WFSless) adaptive optics (AO) systems have been widely studied in recent years. To reach optimum results, such systems require an efficient correction method. This paper presents a fast wavefront correction approach for a WFSless AO system mainly based on the linear phase diversity (PD) technique. The fast closed-loop control algorithm is set up based on the linear relationship between the drive voltage of the deformable mirror (DM) and the far-field images of the system, which is obtained through the linear PD algorithm combined with the influence function of the DM. A large number of phase screens under different turbulence strengths are simulated to test the performance of the proposed method. The numerical simulation results show that the method has fast convergence rate and strong correction ability, a few correction times can achieve good correction results, and can effectively improve the imaging quality of the system while needing fewer measurements of CCD data.

An analysis of optical effects caused by thermally induced mirror deformations.

PubMed

Ogrodnik, R F

1970-09-01

This paper analyzes thermally induced mirror deformations and their resulting wavefront distortions which occur under the conditions of radially nonuniform mirror heating. The analysis is adaptable to heating produced by any radially nonuniform incident radiation. Specific examples of radiation distributions which are considered are the cosine squared and the gaussian and TEM(0, 1) laser distributions. Deformation effects are examined from two aspects, the first of which is the reflected wavefront radial phase distortion profile caused by the thermally induced surface irregularities at the mirror face. These phase distortion effects appear as aberrations in noncoherent optical applications and as the loss of spatial coherence in coherent applications. The second aspect is the gross wavefront bending due to mirror curvature effects. The analysis considers substrate material, geometry, and cooling in order to determine potential deformation controlling factors. Substrate materials are compared, and performance indicators are suggested to aid in selecting an optimum material for a given heating condition. Deformation examples are given for materials of interest and specific absorbed power levels.

Study of the performance of image restoration under different wavefront aberrations

NASA Astrophysics Data System (ADS)

Wang, Xinqiu; Hu, Xinqi

2016-10-01

Image restoration is an effective way to improve the quality of images degraded by wave-front aberrations. If the wave-front aberration is too large, the performance of the image restoration will not be good. In this paper, the relationship between the performance of image restoration and the degree of wave-front aberrations is studied. A set of different wave-front aberrations is constructed by Zernike polynomials, and the corresponding PSF under white-light illumination is calculated. A set of blurred images is then obtained through convolution methods. Next we recover the images with the regularized Richardson-Lucy algorithm and use the RMS of the original image and the homologous deblurred image to evaluate the quality of restoration. Consequently, we determine the range of wave-front errors in which the recovered images are acceptable.

Two dimensional wavefront retrieval using lateral shearing interferometry

NASA Astrophysics Data System (ADS)

Mancilla-Escobar, B.; Malacara-Hernández, Z.; Malacara-Hernández, D.

2018-06-01

A new zonal two-dimensional method for wavefront retrieval from a surface under test using lateral shearing interferometry is presented. A modified Saunders method and phase shifting techniques are combined to generate a method for wavefront reconstruction. The result is a wavefront with an error below 0.7 λ and without any global high frequency filtering. A zonal analysis over square cells along the surfaces is made, obtaining a polynomial expression for the wavefront deformations over each cell. The main advantage of this method over previously published methods is that a global filtering of high spatial frequencies is not present. Thus, a global smoothing of the wavefront deformations is avoided, allowing the detection of deformations with relatively small extensions, that is, with high spatial frequencies. Additionally, local curvature and low order aberration coefficients are obtained in each cell.

Comparison of Modal to Nodal Approaches for Wavefront Correction,

DTIC Science & Technology

1986-02-01

the influence function of the wavefront corrector. (Implicit here is the assumption that the influence function is the same for every node, which is...To implement a nodal correction, the wavefront to be corrected is -. .. decomposed using a basis which is determined by the nodal (actuator) influence ... function of the wavefront corrector. This decomposition results in a set of coefficients which correspond to the drive signal required at the

A hierarchical wavefront reconstruction algorithm for gradient sensors

NASA Astrophysics Data System (ADS)

Bharmal, Nazim; Bitenc, Urban; Basden, Alastair; Myers, Richard

2013-12-01

ELT-scale extreme adaptive optics systems will require new approaches tocompute the wavefront suitably quickly, when the computational burden ofapplying a MVM is no longer practical. An approach is demonstrated here whichis hierarchical in transforming wavefront slopes from a WFS into a wavefront,and then to actuator values. First, simple integration in 1D is used to create1D-wavefront estimates with unknown starting points at the edges of independentspatial domains. Second, these starting points are estimated globally. By thesestarting points are a sub-set of the overall grid where wavefront values are tobe estimated, sparse representations are produced and numerical complexity canbe chosen by the spacing of the starting point grid relative to the overallgrid. Using a combination of algebraic expressions, sparse representation, anda conjugate gradient solver, the number of non-parallelized operations forreconstruction on a 100x100 sub-aperture sized problem is ~600,000 or O(N^3/2),which is approximately the same as for each thread of a MVM solutionparallelized over 100 threads. To reduce the effects of noise propagationwithin each domain, a noise reduction algorithm can be applied which ensuresthe continuity of the wavefront. To apply this additional step has a cost of~1,200,000 operations. We conclude by briefly discussing how the final step ofconverting from wavefront to actuator values can be achieved.

Whole eye wavefront aberrations in Mexican male subjects.

PubMed

Cantú, Roberto; Rosales, Marco A; Tepichín, Eduardo; Curioca, Andrée; Montes, Victor; Bonilla, Julio

2004-01-01

To analyze the characteristics, incidence, and appearance of wavefront aberrations in undilated, normal, unoperated eyes. Eighty-eight eyes of 44 healthy male Mexican subjects (mean age 25.32 years, range 18 to 36 yr) were divided into three groups based on uncorrected visual acuity of greater than or equal to 20/20, 20/30, or 20/40. UCVA measurements were obtained using an Acuity Max computer screen chart. Wavefront aberrations were measured with the Nidek OPD-Scan ARK 10000, Ver. 1.11b. All measurements were carried out at the same center by the same technician during a single session, following manufacturer instructions. Background illumination was 3 Lux. Wavefront aberration measurements for each group were statistically analyzed using StatView; an average eye was characterized and the resulting aberrations were simulated using MATLAB. We obtained wavefront aberration maps for the 20/20 undilated normal unoperated eyes for total, low, and high order aberration coefficients. Wavefront maps for right eyes were practically the same as those for left eyes. Higher aberrations did not contribute substantially to total wavefront analysis. Average aberrations of this "normal eye" will be used as criteria to decide the necessity of wavefront-guided ablation in our facilities. We will focus on the nearly zero average of high order aberrations in this normal whole eye as a reference to be matched.

Atmospherical wavefront phases using the plenoptic sensor (real data)

NASA Astrophysics Data System (ADS)

Rodríguez-Ramos, L. F.; Montilla, I.; Lüke, J. P.; López, R.; Marichal-Hernández, J. G.; Trujillo-Sevilla, J.; Femenía, B.; López, M.; Fernández-Valdivia, J. J.; Puga, M.; Rosa, F.; Rodríguez-Ramos, J. M.

2012-06-01

Plenoptic cameras have been developed the last years as a passive method for 3d scanning, allowing focal stack capture from a single shot. But data recorded by this kind of sensors can also be used to extract the wavefront phases associated to the atmospheric turbulence in an astronomical observation. The terrestrial atmosphere degrades the telescope images due to the diffraction index changes associated to the turbulence. Na artificial Laser Guide Stars (Na-LGS, 90km high) must be used to obtain the reference wavefront phase and the Optical Transfer Function of the system, but they are affected by defocus because of the finite distance to the telescope. Using the telescope as a plenoptic camera allows us to correct the defocus and to recover the wavefront phase tomographically, taking advantage of the two principal characteristics of the plenoptic sensors at the same time: 3D scanning and wavefront sensing. Then, the plenoptic sensors can be studied and used as an alternative wavefront sensor for Adaptive Optics, particularly relevant when Extremely Large Telescopes projects are being undertaken. In this paper, we will present the first observational wavefront phases extracted from real astronomical observations, using punctual and extended objects, and we show that the restored wavefronts match the Kolmogorov atmospheric turbulence.

Zonal wavefront sensor with reduced number of rows in the detector array.

PubMed

Boruah, Bosanta R; Das, Abhijit

2011-07-10

In this paper, we describe a zonal wavefront sensor in which the photodetector array can have a smaller number of rows. The test wavefront is incident on a two-dimensional array of diffraction gratings followed by a single focusing lens. The periodicity and the orientation of the grating rulings of each grating can be chosen such that the +1 order beam from the gratings forms an array of focal spots in the detector plane. We show that by using a square array of zones, it is possible to generate an array of +1 order focal spots having a smaller number of rows, thus reducing the height of the required detector array. The phase profile of the test wavefront can be estimated by measuring the displacements of the +1 order focal spots for the test wavefront relative to the +1 order focal spots for a plane reference wavefront. The narrower width of the photodetector array can offer several advantages, such as a faster frame rate of the wavefront sensor, a reduced amount of cross talk between the nearby detector zones, and a decrease in the maximum thermal noise. We also present experimental results of a proof-of-concept experimental arrangement using the proposed wavefront sensing scheme. © 2011 Optical Society of America

Algorithms to eliminate the influence of non-uniform intensity distributions on wavefront reconstruction by quadri-wave lateral shearing interferometers

NASA Astrophysics Data System (ADS)

Chen, Xiao-jun; Dong, Li-zhi; Wang, Shuai; Yang, Ping; Xu, Bing

2017-11-01

In quadri-wave lateral shearing interferometry (QWLSI), when the intensity distribution of the incident light wave is non-uniform, part of the information of the intensity distribution will couple with the wavefront derivatives to cause wavefront reconstruction errors. In this paper, we propose two algorithms to reduce the influence of a non-uniform intensity distribution on wavefront reconstruction. Our simulation results demonstrate that the reconstructed amplitude distribution (RAD) algorithm can effectively reduce the influence of the intensity distribution on the wavefront reconstruction and that the collected amplitude distribution (CAD) algorithm can almost eliminate it.

Single-Grating Talbot Imaging for Wavefront Sensing and X-Ray Metrology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grizolli, Walan; Shi, Xianbo; Kolodziej, Tomasz

2017-01-01

Single-grating Talbot imaging relies on high-spatial-resolution detectors to perform accurate measurements of X-ray beam wavefronts. The wavefront can be retrieved with a single image, and a typical measurement and data analysis can be performed in few seconds. These qualities make it an ideal tool for synchrotron beamline diagnostics and in-situ metrology. The wavefront measurement can be used both to obtain a phase contrast image of an object and to characterize an X-ray beam. In this work, we explore the concept in two cases: at-wavelength metrology of 2D parabolic beryllium lenses and a wavefront sensor using a diamond crystal beam splitter.

A simple method for evaluating the wavefront compensation error of diffractive liquid-crystal wavefront correctors.

PubMed

Cao, Zhaoliang; Mu, Quanquan; Hu, Lifa; Lu, Xinghai; Xuan, Li

2009-09-28

A simple method for evaluating the wavefront compensation error of diffractive liquid-crystal wavefront correctors (DLCWFCs) for atmospheric turbulence correction is reported. A simple formula which describes the relationship between pixel number, DLCWFC aperture, quantization level, and atmospheric coherence length was derived based on the calculated atmospheric turbulence wavefronts using Kolmogorov atmospheric turbulence theory. It was found that the pixel number across the DLCWFC aperture is a linear function of the telescope aperture and the quantization level, and it is an exponential function of the atmosphere coherence length. These results are useful for people using DLCWFCs in atmospheric turbulence correction for large-aperture telescopes.

Selecting appropriate singular values of transmission matrix to improve precision of incident wavefront retrieval

NASA Astrophysics Data System (ADS)

Fang, Longjie; Zhang, Xicheng; Zuo, Haoyi; Pang, Lin; Yang, Zuogang; Du, Jinglei

2018-06-01

A method of selecting appropriate singular values of the transmission matrix to improve the precision of incident wavefront retrieval in focusing light through scattering media is proposed. The optimal singular values selected by this method can reduce the degree of ill-conditionedness of the transmission matrix effectively, which indicates that the incident wavefront retrieved from the optimal set of singular values is more accurate than the incident wavefront retrieved from other sets of singular values. The validity of this method is verified by numerical simulation and actual measurements of the incident wavefront of coherent light through ground glass.

Estimation of chromatic errors from broadband images for high contrast imaging: sensitivity analysis

NASA Astrophysics Data System (ADS)

Sirbu, Dan; Belikov, Ruslan

2016-01-01

Many concepts have been proposed to enable direct imaging of planets around nearby stars, and which would enable spectroscopic observations of their atmospheric observations and the potential discovery of biomarkers. The main technical challenge associated with direct imaging of exoplanets is to effectively control both the diffraction and scattered light from the star so that the dim planetary companion can be seen. Usage of an internal coronagraph with an adaptive optical system for wavefront correction is one of the most mature methods and is being developed as an instrument addition to the WFIRST-AFTA space mission. In addition, such instruments as GPI and SPHERE are already being used on the ground and are yielding spectra of giant planets. For the deformable mirror (DM) to recover a dark hole region with sufficiently high contrast in the image plane, mid-spatial frequency wavefront errors must be estimated. To date, most broadband lab demonstrations use narrowband filters to obtain an estimate of the the chromaticity of the wavefront error and this can result in usage of a large percentage of the total integration time. Previously, we have proposed a method to estimate the chromaticity of wavefront errors using only broadband images; we have demonstrated that under idealized conditions wavefront errors can be estimated from images composed of discrete wavelengths. This is achieved by using DM probes with sufficient spatially-localized chromatic diversity. Here we report on the results of a study of the performance of this method with respect to realistic broadband images including noise. Additionally, we study optimal probe patterns that enable reduction of the number of probes used and compare the integration time with narrowband and IFS estimation methods.

Massively parallel algorithms for real-time wavefront control of a dense adaptive optics system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fijany, A.; Milman, M.; Redding, D.

1994-12-31

In this paper massively parallel algorithms and architectures for real-time wavefront control of a dense adaptive optic system (SELENE) are presented. The authors have already shown that the computation of a near optimal control algorithm for SELENE can be reduced to the solution of a discrete Poisson equation on a regular domain. Although, this represents an optimal computation, due the large size of the system and the high sampling rate requirement, the implementation of this control algorithm poses a computationally challenging problem since it demands a sustained computational throughput of the order of 10 GFlops. They develop a novel algorithm,more » designated as Fast Invariant Imbedding algorithm, which offers a massive degree of parallelism with simple communication and synchronization requirements. Due to these features, this algorithm is significantly more efficient than other Fast Poisson Solvers for implementation on massively parallel architectures. The authors also discuss two massively parallel, algorithmically specialized, architectures for low-cost and optimal implementation of the Fast Invariant Imbedding algorithm.« less

The Segmented Aperture Interferometric Nulling Testbed (SAINT) I: Overview and Air-side System Description

NASA Technical Reports Server (NTRS)

Hicks, Brian A.; Lyon, Richard G.; Petrone, Peter, III; Bolcar, Matthew R.; Bolognese, Jeff; Clampin, Mark; Dogoda, Peter; Dworzanski, Daniel; Helmbrecht, Michael A.; Koca, Corina;

Wavefront analysis from its slope data

NASA Astrophysics Data System (ADS)

Mahajan, Virendra N.; Acosta, Eva

2017-08-01

In the aberration analysis of a wavefront over a certain domain, the polynomials that are orthogonal over and represent balanced wave aberrations for this domain are used. For example, Zernike circle polynomials are used for the analysis of a circular wavefront. Similarly, the annular polynomials are used to analyze the annular wavefronts for systems with annular pupils, as in a rotationally symmetric two-mirror system, such as the Hubble space telescope. However, when the data available for analysis are the slopes of a wavefront, as, for example, in a Shack- Hartmann sensor, we can integrate the slope data to obtain the wavefront data, and then use the orthogonal polynomials to obtain the aberration coefficients. An alternative is to find vector functions that are orthogonal to the gradients of the wavefront polynomials, and obtain the aberration coefficients directly as the inner products of these functions with the slope data. In this paper, we show that an infinite number of vector functions can be obtained in this manner. We show further that the vector functions that are irrotational are unique and propagate minimum uncorrelated additive random noise from the slope data to the aberration coefficients.

Diffracted wavefront measurement of a volume phase holographic grating at cryogenic temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanche, Pierre-Alexandre; Habraken, Serge; Lemaire, Philippe

2006-09-20

Flatness of the wavefront diffracted by grating can be mandatory for some applications. At ambient temperature, the wavefront diffracted by a volume phase holographic grating (VPHG) is well mastered by the manufacturing process and can be corrected or shaped by post polishing. However, to be used in cooled infrared spectrometers, VPHGs have to stand and work properly at low temperatures.We present the measurement of the wavefront diffracted by atypical VPHG at various temperatures down to 150 K and at several thermal inhomogeneity amplitudes. The particular grating observed was produced using a dichromated gelatine technique and encapsulated between two glass blanks.more » Diffracted wavefront measurements show that the wavefront is extremely stable according to the temperature as long as the latter is homogeneous over the grating stack volume. Increasing the thermal inhomogeneity increases the wavefront error that pinpoints the importance of the final instrument thermal design. This concludes the dichromated gelatine VPHG technology, used more and more in visible spectrometers, can be applied as it is to cooled IR spectrometers.« less

A zonal wavefront sensor with multiple detector planes

NASA Astrophysics Data System (ADS)

Pathak, Biswajit; Boruah, Bosanta R.

2018-03-01

A conventional zonal wavefront sensor estimates the wavefront from the data captured in a single detector plane using a single camera. In this paper, we introduce a zonal wavefront sensor which comprises multiple detector planes instead of a single detector plane. The proposed sensor is based on an array of custom designed plane diffraction gratings followed by a single focusing lens. The laser beam whose wavefront is to be estimated is incident on the grating array and one of the diffracted orders from each grating is focused on the detector plane. The setup, by employing a beam splitter arrangement, facilitates focusing of the diffracted beams on multiple detector planes where multiple cameras can be placed. The use of multiple cameras in the sensor can offer several advantages in the wavefront estimation. For instance, the proposed sensor can provide superior inherent centroid detection accuracy that can not be achieved by the conventional system. It can also provide enhanced dynamic range and reduced crosstalk performance. We present here the results from a proof of principle experimental arrangement that demonstrate the advantages of the proposed wavefront sensing scheme.

Compliant deformable mirror approach for wavefront improvement

NASA Astrophysics Data System (ADS)

Clark, James H.; Penado, F. Ernesto

2016-04-01

We describe a compliant static deformable mirror approach to reduce the wavefront concavity at the Navy Precision Optical Interferometer (NPOI). A single actuator pressing on the back surface of just one of the relay mirrors deforms the front surface in a correcting convex shape. Our design uses the mechanical advantage gained from a force actuator sandwiched between a rear flexure plate and the back surface of the mirror. We superimpose wavefront contour measurements with our finite element deformed mirror model. An example analysis showed improvement from 210-nm concave-concave wavefront to 51-nm concave-concave wavefront. With our present model, a 100-nm actuator increment displaces the mirror surface by 1.1 nm. We describe the need for wavefront improvement that arises from the NPOI reconfigurable array, offer a practical design approach, and analyze the support structure and compliant deformable mirror using the finite element method. We conclude that a 20.3-cm-diameter, 1.9-cm-thick Zerodur® mirror shows that it is possible to deform the reflective surface and cancel out three-fourths of the wavefront deformation without overstressing the material.

Holographic Adaptive Laser Optics System

NASA Astrophysics Data System (ADS)

Andersen, G.; Ghebremichael, F.

2011-09-01

We have created a new adaptive optics system using a holographic modal wavefront sensing method with the autonomous (computer-free) closed-loop control of a MEMS deformable mirror (DM). A multiplexed hologram is recorded using the maximum and minimum actuator positions on the deformable mirror as the “modes”. On reconstruction, an input beam is diffracted into pairs of focal spots and the ratio of the intensities of certain pairs determines the absolute wavefront phase at a particular actuator location. The wavefront measurement is made using fast, sensitive silicon photomultiplier arrays with the parallel outputs directly controlling individual actuators in the MEMS DM. In this talk, we will present the results from an all-optical, ultra-compact system that runs in closed-loop without the need for a computer. The speed is limited only by the response time of any given DM actuator and not the number of actuators. In our case, our 32-actuator prototype device already operates at 10 kHz and our next generation system is being designed for > 100 kHz. As a modal system, it is largely insensitive to scintillation and obscuration and is thus ideal for extreme adaptive optics applications. We will present information on how HALOS can be used for image correction and beam propagation as well as several other novel applications.

Six-month clinical outcomes after hyperopic correction with the SCHWIND AMARIS Total-Tech laser

PubMed Central

Arbelaez, María Clara; Vidal, Camila; Arba Mosquera, Samuel

2011-01-01

Purpose To evaluate postoperative clinical outcomes, and corneal High Order Aberrations, among eyes with hyperopia up to +5 D of spherical equivalent, that have undergone LASIK treatments using the SCHWIND AMARIS laser system. Methods At six-month follow-up, 100 eyes with preoperative hyperopia or hyperopic astigmatism up to +5 D of spherical equivalent were retrospectively analysed. Standard examinations, pre- and postoperative wavefront analysis with a corneal-wavefront-analyzer (OPTIKON Scout) were performed. Aberration-Free aspheric treatments were planned with Custom Ablation Manager software and ablations performed using the SCHWIND AMARIS flying-spot excimer laser system (both SCHWIND eye-tech-solutions). LASIK flaps were created using a LDV femtosecond laser (Ziemer Group) in all cases. Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, and wavefront aberration. Results At six month, 90 % of eyes achieved ≥ 20/25 UCVA and 44 % achieved ≥ 20/16 UCVA. Seventy-four percent of eyes were within ± 0.25D of spherical equivalent and 89 % within ± 0.50D, with 94 % within 0.50D of astigmatism. Mean spherical equivalent was −0.12 ± 0.51D and 0.50 ± 0.51D for the astigmatism. Fifty-two percent of eyes improved BSCVA vs. only 19 % losing lines of BSCVA. Predictability slope for refraction was 1.03 and intercept +0.01 D. On average, negative corneal spherical aberrations were significantly increased by the treatments, no other aberration terms changed from pre- to postoperative values. Conclusions LASIK for hyperopia and hyperopic astigmatism with SCHWIND AMARIS yields very satisfactory visual outcomes. Preoperative refractions were postoperatively reduced to subclinical values with no clinically relevant induction of corneal HOA.

Iterative-Transform Phase Diversity: An Object and Wavefront Recovery Algorithm

NASA Technical Reports Server (NTRS)

Smith, J. Scott

2011-01-01

Presented is a solution for recovering the wavefront and an extended object. It builds upon the VSM architecture and deconvolution algorithms. Simulations are shown for recovering the wavefront and extended object from noisy data.

Volumetric imaging of fast biological dynamics in deep tissue via wavefront engineering

NASA Astrophysics Data System (ADS)

Kong, Lingjie; Tang, Jianyong; Cui, Meng

2016-03-01

To reveal fast biological dynamics in deep tissue, we combine two wavefront engineering methods that were developed in our laboratory, namely optical phase-locked ultrasound lens (OPLUL) based volumetric imaging and iterative multiphoton adaptive compensation technique (IMPACT). OPLUL is used to generate oscillating defocusing wavefront for fast axial scanning, and IMPACT is used to compensate the wavefront distortions for deep tissue imaging. We show its promising applications in neuroscience and immunology.

Geometric Theory of Moving Grid Wavefront Sensor

DTIC Science & Technology

1977-06-30

Identify by block numbot) Adaptive Optics WaVefront Sensor Geometric Optics Analysis Moving Ronchi Grid "ABSTRACT (Continue an revere sdde If nooessaY...ad Identify by block nucber)A geometric optics analysis is made for a wavefront sensor that uses a moving Ronchi grid. It is shown that by simple data... optical systems being considered or being developed -3 for imaging an object through a turbulent atmosphere. Some of these use a wavefront sensor to

Interferometric Shack-Hartmann wavefront sensor with an array of four-hole apertures.

PubMed

López, David; Ríos, Susana

2010-04-20

A modified Hartmann test based on the interference produced by a four-hole mask can be used to measure an unknown wavefront. To scan the wavefront, the interference pattern is measured for different positions of the mask. The position of the central fringe of the diamond-shaped interference pattern gives a measure of the local wavefront slopes. Using a set of four-hole apertures located behind an array of lenslets in such a way that each four-hole window is inside one lenslet area, a set of four-hole interference patterns can be obtained in the back focal plane of the lenslets without having to scan the wavefront. The central fringe area of each interference pattern is narrower than the area of the central maximum of the diffraction pattern of the lenslet, increasing the accuracy in the estimate of the lobe position as compared with the Shack-Hartmann wavefront sensor.

Wavefront measurements of phase plates combining a point-diffraction interferometer and a Hartmann-Shack sensor.

PubMed

Bueno, Juan M; Acosta, Eva; Schwarz, Christina; Artal, Pablo

2010-01-20

A dual setup composed of a point diffraction interferometer (PDI) and a Hartmann-Shack (HS) wavefront sensor was built to compare the estimates of wavefront aberrations provided by the two different and complementary techniques when applied to different phase plates. Results show that under the same experimental and fitting conditions both techniques provide similar information concerning the wavefront aberration map. When taking into account all Zernike terms up to 6th order, the maximum difference in root-mean-square wavefront error was 0.08 microm, and this reduced up to 0.03 microm when excluding lower-order terms. The effects of the pupil size and the order of the Zernike expansion used to reconstruct the wavefront were evaluated. The combination of the two techniques can accurately measure complicated phase profiles, combining the robustness of the HS and the higher resolution and dynamic range of the PDI.

Underwater Turbulence Detection Using Gated Wavefront Sensing Technique

PubMed Central

Bi, Ying; Xu, Xiping; Chow, Eddy Mun Tik

2018-01-01

Laser sensing has been applied in various underwater applications, ranging from underwater detection to laser underwater communications. However, there are several great challenges when profiling underwater turbulence effects. Underwater detection is greatly affected by the turbulence effect, where the acquired image suffers excessive noise, blurring, and deformation. In this paper, we propose a novel underwater turbulence detection method based on a gated wavefront sensing technique. First, we elaborate on the operating principle of gated wavefront sensing and wavefront reconstruction. We then setup an experimental system in order to validate the feasibility of our proposed method. The effect of underwater turbulence on detection is examined at different distances, and under different turbulence levels. The experimental results obtained from our gated wavefront sensing system indicate that underwater turbulence can be detected and analyzed. The proposed gated wavefront sensing system has the advantage of a simple structure and high detection efficiency for underwater environments. PMID:29518889

Automated interferometric alignment system for paraboloidal mirrors

DOEpatents

Maxey, L. Curtis

1993-01-01

A method is described for a systematic method of interpreting interference fringes obtained by using a corner cube retroreflector as an alignment aid when aigning a paraboloid to a spherical wavefront. This is applicable to any general case where such alignment is required, but is specifically applicable in the case of aligning an autocollimating test using a diverging beam wavefront. In addition, the method provides information which can be systematically interpreted such that independent information about pitch, yaw and focus errors can be obtained. Thus, the system lends itself readily to automation. Finally, although the method is developed specifically for paraboloids, it can be seen to be applicable to a variety of other aspheric optics when applied in combination with a wavefront corrector that produces a wavefront which, when reflected from the correctly aligned aspheric surface will produce a collimated wavefront like that obtained from the paraboloid when it is correctly aligned to a spherical wavefront.

Automated interferometric alignment system for paraboloidal mirrors

DOEpatents

Maxey, L.C.

1993-09-28

A method is described for a systematic method of interpreting interference fringes obtained by using a corner cube retroreflector as an alignment aid when aligning a paraboloid to a spherical wavefront. This is applicable to any general case where such alignment is required, but is specifically applicable in the case of aligning an autocollimating test using a diverging beam wavefront. In addition, the method provides information which can be systematically interpreted such that independent information about pitch, yaw and focus errors can be obtained. Thus, the system lends itself readily to automation. Finally, although the method is developed specifically for paraboloids, it can be seen to be applicable to a variety of other aspheric optics when applied in combination with a wavefront corrector that produces a wavefront which, when reflected from the correctly aligned aspheric surface will produce a collimated wavefront like that obtained from the paraboloid when it is correctly aligned to a spherical wavefront. 14 figures.

ARGOS wavefront sensing: from detection to correction

NASA Astrophysics Data System (ADS)

Orban de Xivry, Gilles; Bonaglia, M.; Borelli, J.; Busoni, L.; Connot, C.; Esposito, S.; Gaessler, W.; Kulas, M.; Mazzoni, T.; Puglisi, A.; Rabien, S.; Storm, J.; Ziegleder, J.

2014-08-01

Argos is the ground-layer adaptive optics system for the Large Binocular Telescope. In order to perform its wide-field correction, Argos uses three laser guide stars which sample the atmospheric turbulence. To perform the correction, Argos has at disposal three different wavefront sensing measurements : its three laser guide stars, a NGS tip-tilt, and a third wavefront sensor. We present the wavefront sensing architecture and its individual components, in particular: the finalized Argos pnCCD camera detecting the 3 laser guide stars at 1kHz, high quantum efficiency and 4e- noise; the Argos tip-tilt sensor based on a quad-cell avalanche photo-diodes; and the Argos wavefront computer. Being in the middle of the commissioning, we present the first wavefront sensing configurations and operations performed at LBT, and discuss further improvements in the measurements of the 3 laser guide star slopes as detected by the pnCCD.

Comparison of 2 wavefront-guided excimer lasers for myopic laser in situ keratomileusis: one-year results.

PubMed

Yu, Charles Q; Manche, Edward E

2014-03-01

To compare laser in situ keratomileusis (LASIK) outcomes between 2 wavefront-guided excimer laser systems in the treatment of myopia. University eye clinic, Palo Alto, California, USA. Prospective comparative case series. One eye of patients was treated with the Allegretto Wave Eye-Q system (small-spot scanning laser) and the fellow eye with the Visx Star Customvue S4 IR system (variable-spot scanning laser). Evaluations included measurement of uncorrected visual acuity, corrected visual acuity, and wavefront aberrometry. One hundred eyes (50 patients) were treated. The mean preoperative spherical equivalent (SE) refraction was -3.89 diopters (D) ± 1.67 (SD) and -4.18 ± 1.73 D in the small-spot scanning laser group and variable-spot scanning laser group, respectively. There were no significant differences in preoperative higher-order aberrations (HOAs) between the groups. Twelve months postoperatively, all eyes in the small-spot scanning laser group and 92% in the variable-spot scanning laser group were within ±0.50 D of the intended correction (P = .04). At that time, the small-spot scanning laser group had significantly less spherical aberration (0.12 versus 0.15) (P = .04) and significantly less mean total higher-order root mean square (0.33 μm versus 0.40 μm) (P = .01). Subjectively, patients reported that the clarity of night and day vision was significantly better in the eye treated with the small-spot scanning laser. The predictability and self-reported clarity of vision of wavefront-guided LASIK were better with the small-spot scanning laser. Eyes treated with the small-spot scanning laser had significantly fewer HOAs. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Transverse Pupil Shifts for Adaptive Optics Non-Common Path Calibration

NASA Technical Reports Server (NTRS)

Bloemhof, Eric E.

2011-01-01

A simple new way of obtaining absolute wavefront measurements with a laboratory Fizeau interferometer was recently devised. In that case, the observed wavefront map is the difference of two cavity surfaces, those of the mirror under test and of an unknown reference surface on the Fizeau s transmission flat. The absolute surface of each can be determined by applying standard wavefront reconstruction techniques to two grids of absolute surface height differences of the mirror under test, obtained from pairs of measurements made with slight transverse shifts in X and Y. Adaptive optics systems typically provide an actuated periscope between wavefront sensor (WFS) and commonmode optics, used for lateral registration of deformable mirror (DM) to WFS. This periscope permits independent adjustment of either pupil or focal spot incident on the WFS. It would be used to give the required lateral pupil motion between common and non-common segments, analogous to the lateral shifts of the two phase contributions in the lab Fizeau. The technique is based on a completely new approach to calibration of phase. It offers unusual flexibility with regard to the transverse spatial frequency scales probed, and will give results quite quickly, making use of no auxiliary equipment other than that built into the adaptive optics system. The new technique may be applied to provide novel calibration information about other optical systems in which the beam may be shifted transversely in a controlled way.

Experimental study of an off-axis three mirror anastigmatic system with wavefront coding technology.

PubMed

Yan, Feng; Tao, Xiaoping

2012-04-10

Wavefront coding (WFC) is a kind of computational imaging technique that controls defocus and defocus related aberrations of optical systems by introducing a specially designed phase distribution to the pupil function. This technology has been applied in many imaging systems to improve performance and/or reduce cost. The application of WFC technology in an off-axis three mirror anastigmatic (TMA) system has been proposed, and the design and optimization of optics, the restoration of degraded images, and the manufacturing of wavefront coded elements have been researched in our previous work. In this paper, we describe the alignment, the imaging experiment, and the image restoration of the off-axis TMA system with WFC technology. The ideal wavefront map is set to be the system error of the interferometer to simplify the assembly, and the coefficients of certain Zernike polynomials are monitored to verify the result in the alignment process. A pinhole of 20 μm diameter and the third plate of WT1005-62 resolution patterns are selected as the targets in the imaging experiment. The comparison of the tail lengths of point spread functions is represented to show the invariance of the image quality in the extended depth of focus. The structure similarity is applied to estimate the relationship among the captured images with varying defocus. We conclude that the experiment results agree with the earlier theoretical analysis.

Novel algorithm implementations in DARC: the Durham AO real-time controller

NASA Astrophysics Data System (ADS)

Basden, Alastair; Bitenc, Urban; Jenkins, David

2016-07-01

The Durham AO Real-time Controller has been used on-sky with the CANARY AO demonstrator instrument since 2010, and is also used to provide control for several AO test-benches, including DRAGON. Over this period, many new real-time algorithms have been developed, implemented and demonstrated, leading to performance improvements for CANARY. Additionally, the computational performance of this real-time system has continued to improve. Here, we provide details about recent updates and changes made to DARC, and the relevance of these updates, including new algorithms, to forthcoming AO systems. We present the computational performance of DARC when used on different hardware platforms, including hardware accelerators, and determine the relevance and potential for ELT scale systems. Recent updates to DARC have included algorithms to handle elongated laser guide star images, including correlation wavefront sensing, with options to automatically update references during AO loop operation. Additionally, sub-aperture masking options have been developed to increase signal to noise ratio when operating with non-symmetrical wavefront sensor images. The development of end-user tools has progressed with new options for configuration and control of the system. New wavefront sensor camera models and DM models have been integrated with the system, increasing the number of possible hardware configurations available, and a fully open-source AO system is now a reality, including drivers necessary for commercial cameras and DMs. The computational performance of DARC makes it suitable for ELT scale systems when implemented on suitable hardware. We present tests made on different hardware platforms, along with the strategies taken to optimise DARC for these systems.

Bicubic uniform B-spline wavefront fitting technology applied in computer-generated holograms

NASA Astrophysics Data System (ADS)

Cao, Hui; Sun, Jun-qiang; Chen, Guo-jie

2006-02-01

This paper presented a bicubic uniform B-spline wavefront fitting technology to figure out the analytical expression for object wavefront used in Computer-Generated Holograms (CGHs). In many cases, to decrease the difficulty of optical processing, off-axis CGHs rather than complex aspherical surface elements are used in modern advanced military optical systems. In order to design and fabricate off-axis CGH, we have to fit out the analytical expression for object wavefront. Zernike Polynomial is competent for fitting wavefront of centrosymmetric optical systems, but not for axisymmetrical optical systems. Although adopting high-degree polynomials fitting method would achieve higher fitting precision in all fitting nodes, the greatest shortcoming of this method is that any departure from the fitting nodes would result in great fitting error, which is so-called pulsation phenomenon. Furthermore, high-degree polynomials fitting method would increase the calculation time in coding computer-generated hologram and solving basic equation. Basing on the basis function of cubic uniform B-spline and the character mesh of bicubic uniform B-spline wavefront, bicubic uniform B-spline wavefront are described as the product of a series of matrices. Employing standard MATLAB routines, four kinds of different analytical expressions for object wavefront are fitted out by bicubic uniform B-spline as well as high-degree polynomials. Calculation results indicate that, compared with high-degree polynomials, bicubic uniform B-spline is a more competitive method to fit out the analytical expression for object wavefront used in off-axis CGH, for its higher fitting precision and C2 continuity.

Tomographic active optical trapping of arbitrarily shaped objects by exploiting 3D refractive index maps

NASA Astrophysics Data System (ADS)

Kim, Kyoohyun; Park, Yongkeun

2017-05-01

Optical trapping can manipulate the three-dimensional (3D) motion of spherical particles based on the simple prediction of optical forces and the responding motion of samples. However, controlling the 3D behaviour of non-spherical particles with arbitrary orientations is extremely challenging, due to experimental difficulties and extensive computations. Here, we achieve the real-time optical control of arbitrarily shaped particles by combining the wavefront shaping of a trapping beam and measurements of the 3D refractive index distribution of samples. Engineering the 3D light field distribution of a trapping beam based on the measured 3D refractive index map of samples generates a light mould, which can manipulate colloidal and biological samples with arbitrary orientations and/or shapes. The present method provides stable control of the orientation and assembly of arbitrarily shaped particles without knowing a priori information about the sample geometry. The proposed method can be directly applied in biophotonics and soft matter physics.

Fixed mount wavefront sensor

DOEpatents

Neal, Daniel R.

2000-01-01

A rigid mount and method of mounting for a wavefront sensor. A wavefront dissector, such as a lenslet array, is rigidly mounted at a fixed distance relative to an imager, such as a CCD camera, without need for a relay imaging lens therebetween.

Hybrid Architecture Active Wavefront Sensing and Control

NASA Technical Reports Server (NTRS)

Feinberg, Lee; Dean, Bruce; Hyde, Tupper

2010-01-01

A method was developed for performing relatively high-speed wavefront sensing and control to overcome thermal instabilities in a segmented primary mirror telescope [e.g., James Webb Space Telescope (JWST) at L2], by using the onboard fine guidance sensor (FGS) to minimize expense and complexity. This FGS performs centroiding on a bright star to feed the information to the pointing and control system. The proposed concept is to beam split the image of the guide star (or use a single defocused guide star image) to perform wavefront sensing using phase retrieval techniques. Using the fine guidance sensor star image for guiding and fine phasing eliminates the need for other, more complex ways of achieving very accurate sensing and control that is needed for UV-optical applications. The phase retrieval occurs nearly constantly, so passive thermal stability over fourteen days is not required. Using the FGS as the sensor, one can feed segment update information to actuators on the primary mirror that can update the primary mirror segment fine phasing with this frequency. Because the thermal time constants of the primary mirror are very slow compared to this duration, the mirror will appear extremely stable during observations (to the level of accuracy of the sensing and control). The sensing can use the same phase retrieval techniques as the JWST by employing an additional beam splitter, and having each channel go through a weak lens (one positive and one negative). The channels can use common or separate detectors. Phase retrieval can be performed onboard. The actuation scheme would include a coarse stage able to achieve initial alignment of several millimeters of range (similar to JWST and can use a JWST heritage sensing approach in the science camera) and a fine stage capable of continual updates.

A Future Large-Aperture UVOIR Space Observatory: Key Technologies and Capabilities

NASA Technical Reports Server (NTRS)

Bolcar, Matthew Ryan; Stahle, Carl M.; Balasubramaniam, Kunjithapatham; Clampin, Mark; Feinberg, Lee D.; Mosier, Gary E.; Quijada, Manuel A.; Rauscher, Bernard J.; Redding, David C.; Rioux, Norman M.;

The Advanced Technology Large-Aperture Space Telescope (ATLAST) Technology Roadmap

NASA Technical Reports Server (NTRS)

Stahle, Carl; Balasubramanian, K.; Bolcar, M.; Clampin, M.; Feinberg, L.; Hartman, K.; Mosier, C.; Quijada, M.; Rauscher, B.; Redding, D.;

Wavefront Sensing With Switched Lenses for Defocus Diversity

NASA Technical Reports Server (NTRS)

Dean, Bruce H.

2007-01-01

In an alternative hardware design for an apparatus used in image-based wavefront sensing, defocus diversity is introduced by means of fixed lenses that are mounted in a filter wheel (see figure) so that they can be alternately switched into a position in front of the focal plane of an electronic camera recording the image formed by the optical system under test. [The terms image-based, wavefront sensing, and defocus diversity are defined in the first of the three immediately preceding articles, Broadband Phase Retrieval for Image-Based Wavefront Sensing (GSC-14899-1).] Each lens in the filter wheel is designed so that the optical effect of placing it at the assigned position is equivalent to the optical effect of translating the camera a specified defocus distance along the optical axis. Heretofore, defocus diversity has been obtained by translating the imaging camera along the optical axis to various defocus positions. Because data must be taken at multiple, accurately measured defocus positions, it is necessary to mount the camera on a precise translation stage that must be calibrated for each defocus position and/or to use an optical encoder for measurement and feedback control of the defocus positions. Additional latency is introduced into the wavefront sensing process as the camera is translated to the various defocus positions. Moreover, if the optical system under test has a large focal length, the required defocus values are large, making it necessary to use a correspondingly bulky translation stage. By eliminating the need for translation of the camera, the alternative design simplifies and accelerates the wavefront-sensing process. This design is cost-effective in that the filterwheel/lens mechanism can be built from commercial catalog components. After initial calibration of the defocus value of each lens, a selected defocus value is introduced by simply rotating the filter wheel to place the corresponding lens in front of the camera. The rotation of the wheel can be automated by use of a motor drive, and further calibration is not necessary. Because a camera-translation stage is no longer needed, the size of the overall apparatus can be correspondingly reduced.

Real-time implementing wavefront reconstruction for adaptive optics

NASA Astrophysics Data System (ADS)

Wang, Caixia; Li, Mei; Wang, Chunhong; Zhou, Luchun; Jiang, Wenhan

2004-12-01

The capability of real time wave-front reconstruction is important for an adaptive optics (AO) system. The bandwidth of system and the real-time processing ability of the wave-front processor is mainly affected by the speed of calculation. The system requires enough number of subapertures and high sampling frequency to compensate atmospheric turbulence. The number of reconstruction operation is increased accordingly. Since the performance of AO system improves with the decrease of calculation latency, it is necessary to study how to increase the speed of wavefront reconstruction. There are two methods to improve the real time of the reconstruction. One is to convert the wavefront reconstruction matrix, such as by wavelet or FFT. The other is enhancing the performance of the processing element. Analysis shows that the latency cutting is performed with the cost of reconstruction precision by the former method. In this article, the latter method is adopted. From the characteristic of the wavefront reconstruction algorithm, a systolic array by FPGA is properly designed to implement real-time wavefront reconstruction. The system delay is reduced greatly by the utilization of pipeline and parallel processing. The minimum latency of reconstruction is the reconstruction calculation of one subaperture.

Optimal reconstruction for closed-loop ground-layer adaptive optics with elongated spots.

PubMed

Béchet, Clémentine; Tallon, Michel; Tallon-Bosc, Isabelle; Thiébaut, Éric; Le Louarn, Miska; Clare, Richard M

2010-11-01

The design of the laser-guide-star-based adaptive optics (AO) systems for the Extremely Large Telescopes requires careful study of the issue of elongated spots produced on Shack-Hartmann wavefront sensors. The importance of a correct modeling of the nonuniformity and correlations of the noise induced by this elongation has already been demonstrated for wavefront reconstruction. We report here on the first (to our knowledge) end-to-end simulations of closed-loop ground-layer AO with laser guide stars with such an improved noise model. The results are compared with the level of performance predicted by a classical noise model for the reconstruction. The performance is studied in terms of ensquared energy and confirms that, thanks to the improved noise model, central or side launching of the lasers does not affect the performance with respect to the laser guide stars' flux. These two launching schemes also perform similarly whatever the atmospheric turbulence strength.

Adaptive ophthalmologic system

DOEpatents

Olivier, Scot S.; Thompson, Charles A.; Bauman, Brian J.; Jones, Steve M.; Gavel, Don T.; Awwal, Abdul A.; Eisenbies, Stephen K.; Haney, Steven J.

2007-03-27

A system for improving vision that can diagnose monochromatic aberrations within a subject's eyes, apply the wavefront correction, and then enable the patient to view the results of the correction. The system utilizes a laser for producing a beam of light; a corrector; a wavefront sensor; a testing unit; an optic device for directing the beam of light to the corrector, to the retina, from the retina to the wavefront sensor, and to the testing unit; and a computer operatively connected to the wavefront sensor and the corrector.

JWFront: Wavefronts and Light Cones for Kerr Spacetimes

NASA Astrophysics Data System (ADS)

Frutos Alfaro, Francisco; Grave, Frank; Müller, Thomas; Adis, Daria

2015-04-01

JWFront visualizes wavefronts and light cones in general relativity. The interactive front-end allows users to enter the initial position values and choose the values for mass and angular momentum per unit mass. The wavefront animations are available in 2D and 3D; the light cones are visualized using the coordinate systems (t, x, y) or (t, z, x). JWFront can be easily modified to simulate wavefronts and light cones for other spacetime by providing the Christoffel symbols in the program.

Advanced Telescopes and Observatories Capability Roadmap Presentation to the NRC

NASA Technical Reports Server (NTRS)

2005-01-01

This viewgraph presentation provides an overview of the NASA Advanced Planning and Integration Office (APIO) roadmap for developing technological capabilities for telescopes and observatories in the following areas: Optics; Wavefront Sensing and Control and Interferometry; Distributed and Advanced Spacecraft; Large Precision Structures; Cryogenic and Thermal Control Systems; Infrastructure.

First-passage times for pattern formation in nonlocal partial differential equations

NASA Astrophysics Data System (ADS)

Cáceres, Manuel O.; Fuentes, Miguel A.

2015-10-01

We describe the lifetimes associated with the stochastic evolution from an unstable uniform state to a patterned one when the time evolution of the field is controlled by a nonlocal Fisher equation. A small noise is added to the evolution equation to define the lifetimes and to calculate the mean first-passage time of the stochastic field through a given threshold value, before the patterned steady state is reached. In order to obtain analytical results we introduce a stochastic multiscale perturbation expansion. This multiscale expansion can also be used to tackle multiplicative stochastic partial differential equations. A critical slowing down is predicted for the marginal case when the Fourier phase of the unstable initial condition is null. We carry out Monte Carlo simulations to show the agreement with our theoretical predictions. Analytic results for the bifurcation point and asymptotic analysis of traveling wave-front solutions are included to get insight into the noise-induced transition phenomena mediated by invading fronts.

First-passage times for pattern formation in nonlocal partial differential equations.

PubMed

Cáceres, Manuel O; Fuentes, Miguel A

2015-10-01

We describe the lifetimes associated with the stochastic evolution from an unstable uniform state to a patterned one when the time evolution of the field is controlled by a nonlocal Fisher equation. A small noise is added to the evolution equation to define the lifetimes and to calculate the mean first-passage time of the stochastic field through a given threshold value, before the patterned steady state is reached. In order to obtain analytical results we introduce a stochastic multiscale perturbation expansion. This multiscale expansion can also be used to tackle multiplicative stochastic partial differential equations. A critical slowing down is predicted for the marginal case when the Fourier phase of the unstable initial condition is null. We carry out Monte Carlo simulations to show the agreement with our theoretical predictions. Analytic results for the bifurcation point and asymptotic analysis of traveling wave-front solutions are included to get insight into the noise-induced transition phenomena mediated by invading fronts.

Dynamic Patterns of Modern Epidemics

NASA Astrophysics Data System (ADS)

Brockmann, Dirk; Hufnagel, Lars; Geisel, Theo

2004-03-01

We investigate the effects of scale-free travelling of humans and their inhomogeneous geographic distribution on the dynamic patterns of spreading epidemics. Our approach combines the susceptible/infected/recovered paradigm for the infection dynamics with superdiffusive dispersion of individuals and their inhomogeneous spatial distribution. We show that scale-free motion of individuals and their variable spatial distribution leads to the absence of wavefronts in dynamic epidemic patterns which are typical for the limiting cases of ordinary diffusion and spatially homogeneous populations. Instead, patterns emerge with isolated hotspots on highly populated areas from which regional epidemic outbursts are triggered. Hotspot sizes are independent of the correlation length in the spatial distribution of individuals and occur on all scales. Our theory predicts that highly populated areas are reached by an epidemic in advance and must receive special attention in control measure strategies. Furthermore, our analysis predicts strong fluctuations in the time course of the total infection which cannot be accounted for by ordinary reaction-diffusion models for epidemics.

The AOLI low-order non-linear curvature wavefront sensor: laboratory and on-sky results

NASA Astrophysics Data System (ADS)

Crass, Jonathan; King, David; MacKay, Craig

2014-08-01

Many adaptive optics (AO) systems in use today require the use of bright reference objects to determine the effects of atmospheric distortions. Typically these systems use Shack-Hartmann Wavefront sensors (SHWFS) to distribute incoming light from a reference object between a large number of sub-apertures. Guyon et al. evaluated the sensitivity of several different wavefront sensing techniques and proposed the non-linear Curvature Wavefront Sensor (nlCWFS) offering improved sensitivity across a range of orders of distortion. On large ground-based telescopes this can provide nearly 100% sky coverage using natural guide stars. We present work being undertaken on the nlCWFS development for the Adaptive Optics Lucky Imager (AOLI) project. The wavefront sensor is being developed as part of a low-order adaptive optics system for use in a dedicated instrument providing an AO corrected beam to a Lucky Imaging based science detector. The nlCWFS provides a total of four reference images on two photon-counting EMCCDs for use in the wavefront reconstruction process. We present results from both laboratory work using a calibration system and the first on-sky data obtained with the nlCWFS at the 4.2 metre William Herschel Telescope, La Palma. In addition, we describe the updated optical design of the wavefront sensor, strategies for minimising intrinsic effects and methods to maximise sensitivity using photon-counting detectors. We discuss on-going work to develop the high speed reconstruction algorithm required for the nlCWFS technique. This includes strategies to implement the technique on graphics processing units (GPUs) and to minimise computing overheads to obtain a prior for a rapid convergence of the wavefront reconstruction. Finally we evaluate the sensitivity of the wavefront sensor based upon both data and low-photon count strategies.

Stability of therapeutic retreatment of corneal wavefront customized ablation with the SCHWIND CAM: 4-year data.

PubMed

Aslanides, Ioannis M; Kolli, Sai; Padroni, Sara; Padron, Sara; Arba Mosquera, Samuel

2012-05-01

To evaluate the long-term outcomes of aspheric corneal wavefront ablation profiles for excimer laser retreatment. Eighteen eyes that had previously undergone LASIK or photorefractive keratectomy (PRK) were retreated with LASIK using the corneal wavefront ablation profile. Custom Ablation Manager (SCHWIND eye-tech-solutions, Kleinostheim, Germany) software and the ESIRIS flying spot excimer laser system (SCHWIND) were used to perform the ablations. Refractive outcomes and wavefront data are reported up to 4 years after retreatment. Pre- and postoperative data were compared with Student t tests and (multivariate) correlation tests. P<.05 was considered statistically significant. A bilinear correlation of various postoperative wavefront aberrations versus planned correction and preoperative aberration was performed. Mean manifest refraction spherical equivalent (MRSE) before retreatment was -0.38±1.85 diopters (D) and -0.09±0.22 D at 6 months and -0.10±0.38 D at 4 years postoperatively. The reduction in MRSE was statistically significant at both postoperative time points (P<.005). Postoperative aberrations were statistically lower (spherical aberration P<.05; coma P<.005; root-mean-square higher order aberration P<.0001) at 4 years postoperatively. Distribution of the postoperative uncorrected distance visual acuity (P<.0001) and corrected distance visual acuity (P<.01) were statistically better than preoperative values. Aspheric corneal wavefront customization with the ESIRIS yields visual, optical, and refractive results comparable to those of other wavefront-guided customized techniques for the correction of myopia and myopic astigmatism. The corneal wavefront customized approach shows its strength in cases where abnormal optical systems are expected. Systematic wavefront customized corneal ablation appears safe and efficacious for retreatment cases. Copyright 2012, SLACK Incorporated.

Optical properties of the mouse eye

PubMed Central

Geng, Ying; Schery, Lee Anne; Sharma, Robin; Dubra, Alfredo; Ahmad, Kamran; Libby, Richard T.; Williams, David R.

2011-01-01

The Shack-Hartmann wavefront sensor (SHWS) spots upon which ocular aberration measurements depend have poor quality in mice due to light reflected from multiple retinal layers. We have designed and implemented a SHWS that can favor light from a specific retinal layer and measured monochromatic aberrations in 20 eyes from 10 anesthetized C57BL/6J mice. Using this instrument, we show that mice are myopic, not hyperopic as is frequently reported. We have also measured longitudinal chromatic aberration (LCA) of the mouse eye and found that it follows predictions of the water-filled schematic mouse eye. Results indicate that the optical quality of the mouse eye assessed by measurement of its aberrations is remarkably good, better for retinal imaging than the human eye. The dilated mouse eye has a much larger numerical aperture (NA) than that of the dilated human eye (0.5 NA vs. 0.2 NA), but it has a similar amount of root mean square (RMS) higher order aberrations compared to the dilated human eye. These measurements predict that adaptive optics based on this method of wavefront sensing will provide improvements in retinal image quality and potentially two times higher lateral resolution than that in the human eye. PMID:21483598

Preprocessed cumulative reconstructor with domain decomposition: a fast wavefront reconstruction method for pyramid wavefront sensor.

PubMed

Shatokhina, Iuliia; Obereder, Andreas; Rosensteiner, Matthias; Ramlau, Ronny

2013-04-20

We present a fast method for the wavefront reconstruction from pyramid wavefront sensor (P-WFS) measurements. The method is based on an analytical relation between pyramid and Shack-Hartmann sensor (SH-WFS) data. The algorithm consists of two steps--a transformation of the P-WFS data to SH data, followed by the application of cumulative reconstructor with domain decomposition, a wavefront reconstructor from SH-WFS measurements. The closed loop simulations confirm that our method provides the same quality as the standard matrix vector multiplication method. A complexity analysis as well as speed tests confirm that the method is very fast. Thus, the method can be used on extremely large telescopes, e.g., for eXtreme adaptive optics systems.

Sequential deconvolution from wave-front sensing using bivariate simplex splines

NASA Astrophysics Data System (ADS)

Guo, Shiping; Zhang, Rongzhi; Li, Jisheng; Zou, Jianhua; Xu, Rong; Liu, Changhai

2015-05-01

Deconvolution from wave-front sensing (DWFS) is an imaging compensation technique for turbulence degraded images based on simultaneous recording of short exposure images and wave-front sensor data. This paper employs the multivariate splines method for the sequential DWFS: a bivariate simplex splines based average slopes measurement model is built firstly for Shack-Hartmann wave-front sensor; next, a well-conditioned least squares estimator for the spline coefficients is constructed using multiple Shack-Hartmann measurements; then, the distorted wave-front is uniquely determined by the estimated spline coefficients; the object image is finally obtained by non-blind deconvolution processing. Simulated experiments in different turbulence strength show that our method performs superior image restoration results and noise rejection capability especially when extracting the multidirectional phase derivatives.

Maximum-likelihood methods in wavefront sensing: stochastic models and likelihood functions

PubMed Central

Barrett, Harrison H.; Dainty, Christopher; Lara, David

2008-01-01

Maximum-likelihood (ML) estimation in wavefront sensing requires careful attention to all noise sources and all factors that influence the sensor data. We present detailed probability density functions for the output of the image detector in a wavefront sensor, conditional not only on wavefront parameters but also on various nuisance parameters. Practical ways of dealing with nuisance parameters are described, and final expressions for likelihoods and Fisher information matrices are derived. The theory is illustrated by discussing Shack–Hartmann sensors, and computational requirements are discussed. Simulation results show that ML estimation can significantly increase the dynamic range of a Shack–Hartmann sensor with four detectors and that it can reduce the residual wavefront error when compared with traditional methods. PMID:17206255

Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

PubMed Central

Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

2013-01-01

We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

Wavefront sensing, control, and pointing

NASA Technical Reports Server (NTRS)

Pitts, Thomas; Sevaston, George; Agronin, Michael; Bely, Pierre; Colavita, Mark; Clampin, Mark; Harvey, James; Idell, Paul; Sandler, Dave; Ulmer, Melville

1992-01-01

A majority of future NASA astrophysics missions from orbiting interferometers to 16-m telescopes on the Moon have, as a common requirement, the need to bring light from a large entrance aperture to the focal plane in a way that preserves the spatial coherence properties of the starlight. Only by preserving the phase of the incoming wavefront, can many scientific observations be made, observations that range from measuring the red shift of quasi-stellar objects (QSO's) to detecting the IR emission of a planet in orbit around another star. New technologies for wavefront sensing, control, and pointing hold the key to advancing our observatories of the future from those already launched or currently under development. As the size of the optical system increases, either to increase the sensitivity or angular resolution of the instrument, traditional technologies for maintaining optical wavefront accuracy become prohibitively expensive or completely impractical. For space-based instruments, the low mass requirement and the large temperature excursions further challenge existing technologies. The Hubble Space Telescope (HST) is probably the last large space telescope to rely on passive means to keep its primary optics stable and the optical system aligned. One needs only look to the significant developments in wavefront sensing, control, and pointing that have occurred over the past several years to appreciate the potential of this technology for transforming the capability of future space observatories. Future developments in space-borne telescopes will be based in part on developments in ground-based systems. Telescopes with rigid primary mirrors much larger than 5 m in diameter are impractical because of gravity loading. New technologies are now being introduced, such as active optics, that address the scale problem and that allow very large telescopes to be built. One approach is a segmented design such as that being pioneered by the W.M. Keck telescope now under construction at the Mauna Kea Observatory. It consists of 36 hexagonal mirror segments, supported on a framework structure, which are positioned by actuators located between the structure and the mirrors. The figure of the telescope is initialized by making observations of a bright star using a Shack Hartmann sensor integrated with a white light interferometer. Then, using sensed data from the mirror edges to control these actuators, the figure of the mosaic of 36 segments is maintained as if it were a rigid primary mirror. Another active optics approach is the use of a thin meniscus mirror with actuators. This technique was demonstrated on the European Southern Observatory's New Technology Telescope (NTT) and is planned for use in the Very Large Telescope (consists of four 8-m apertures), which is now entering the design phase.

Zyoptix wavefront-guided versus standard photorefractive keratectomy (PRK) in low and moderate myopia: randomized controlled 6-month study.

PubMed

Mastropasqua, L; Toto, L; Zuppardi, E; Nubile, M; Carpineto, P; Di Nicola, M; Ballone, E

2006-01-01

To evaluate the refractive and aberrometric outcome of wavefront-guided photorefractive keratectomy (PRK) compared to standard PRK in myopic patients. Fifty-six eyes of 56 patients were included in the study and were randomly divided into two groups. The study group consisted of 28 eyes with a mean spherical equivalent (SE) of -2.25+/-0.76 diopters (D) (range: -1.5 to -3.5 D) treated with wavefront-guided PRK using the Zywave ablation profile and the Bausch & Lomb Technolas 217z excimer laser (Zyoptix system) and the control group included 28 eyes with a SE of -2.35+/-1.01 D (range: -1.5 to -3.5 D) treated with standard PRK (PlanoScan ablation) using the same laser. A Zywave aberrometer was used to analyze and calculate the root-mean-square (RMS) of total high order aberrations (HOA) and Zernike coefficients of third and fourth order before and after (over a 6-month follow-up period) surgery in both groups. Preoperative and postoperative SE, un-corrected visual acuity (UCVA), and best-corrected visual acuity (BCVA) were evaluated in all cases. There was a high correlation between achieved and intended correction. The differences between the two treatment groups were not statistically significant for UCVA, BCVA, or SE cycloplegic refraction . Postoperatively the RMS value of high order aberrations was raised in both groups. At 6-month control, on average it increased by a factor of 1.17 in the Zyoptix PRK group and 1.54 in the PlanoScan PRK group (p=0.22). In the Zyoptix group there was a decrease of coma aberration, while in the PlanoScan group this third order aberration increased. The difference between postoperative and preoperative values between the two groups was statistically significant for coma aberration (p=0.013). No statistically significant difference was observed for spherical-like aberration between the two groups. In the study group eyes with a low amount of preoperative aberrations (HOA RMS lower than the median value; <0.28 microm) showed an increase of HOA RMS while eyes with RMS higher than 0.28 microm showed a decrease (p<0.05). Zyoptix wavefront-guided PRK is as safe and efficacious for the correction of myopia and myopic astigmatism as PlanoScan PRK. Moreover this technique induces a smaller increase of third order coma aberration compared to standard PRK. The use of Zyoptix wavefront-guided PRK is particularly indicated in eyes with higher preoperative RMS values.

75 FR 28663 - Government-Owned Inventions, Available for Licensing

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-21

...- Destruct Capability. NASA Case No. GSC-15464-1: Optical Wave-Front Recovery for Active and Adaptive Imaging Control. NASA Case No. GSC-15732-1: Wind and Temperature Spectrometer with Crossed Small-Deflection Energy...

Phase unwrapping with a virtual Hartmann-Shack wavefront sensor.

PubMed

Akondi, Vyas; Falldorf, Claas; Marcos, Susana; Vohnsen, Brian

2015-10-05

The use of a spatial light modulator for implementing a digital phase-shifting (PS) point diffraction interferometer (PDI) allows tunability in fringe spacing and in achieving PS without the need for mechanically moving parts. However, a small amount of detector or scatter noise could affect the accuracy of wavefront sensing. Here, a novel method of wavefront reconstruction incorporating a virtual Hartmann-Shack (HS) wavefront sensor is proposed that allows easy tuning of several wavefront sensor parameters. The proposed method was tested and compared with a Fourier unwrapping method implemented on a digital PS PDI. The rewrapping of the Fourier reconstructed wavefronts resulted in phase maps that matched well the original wrapped phase and the performance was found to be more stable and accurate than conventional methods. Through simulation studies, the superiority of the proposed virtual HS phase unwrapping method is shown in comparison with the Fourier unwrapping method in the presence of noise. Further, combining the two methods could improve accuracy when the signal-to-noise ratio is sufficiently high.

Estimating stochastic noise using in situ measurements from a linear wavefront slope sensor.

PubMed

Bharmal, Nazim Ali; Reeves, Andrew P

2016-01-15

It is shown how the solenoidal component of noise from the measurements of a wavefront slope sensor can be utilized to estimate the total noise: specifically, the ensemble noise variance. It is well known that solenoidal noise is orthogonal to the reconstruction of the wavefront under conditions of low scintillation (absence of wavefront vortices). Therefore, it can be retrieved even with a nonzero slope signal present. By explicitly estimating the solenoidal noise from an ensemble of slopes, it can be retrieved for any wavefront sensor configuration. Furthermore, the ensemble variance is demonstrated to be related to the total noise variance via a straightforward relationship. This relationship is revealed via the method of the explicit estimation: it consists of a small, heuristic set of four constants that do not depend on the underlying statistics of the incoming wavefront. These constants seem to apply to all situations-data from a laboratory experiment as well as many configurations of numerical simulation-so the method is concluded to be generic.

An optical wavefront sensor based on a double layer microlens array.

PubMed

Lin, Vinna; Wei, Hsiang-Chun; Hsieh, Hsin-Ta; Su, Guo-Dung John

2011-01-01

In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA) to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS) above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin), the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution.

Simple broadband implementation of a phase contrast wavefront sensor for adaptive optics

NASA Technical Reports Server (NTRS)

Bloemhof, E. E.; Wallace, J. K.

2004-01-01

The most critical element of an adaptive optics system is its wavefront sensor, which must measure the closed-loop difference between the corrected wavefront and an ideal template at high speed, in real time, over a dense sampling of the pupil. Most high-order systems have used Shack-Hartmann wavefront sensors, but a novel approach based on Zernike's phase contrast principle appears promising. In this paper we discuss a simple way to achromatize such a phase contrast wavefront sensor, using the pi/2 phase difference between reflected and transmitted rays in a thin, symmetric beam splitter. We further model the response at a range of wavelengths to show that the required transverse dimension of the focal-plane phase-shifting spot, nominally lambda/D, may not be very sensitive to wavelength, and so in practice additional optics to introduce wavelength-dependent transverse magnification achromatizing this spot diameter may not be required. A very simple broadband implementation of the phase contrast wavefront sensor results.

Complex wavefront sensing with a plenoptic sensor

NASA Astrophysics Data System (ADS)

Wu, Chensheng; Ko, Jonathan; Davis, Christopher C.

2016-09-01

There are many techniques to achieve basic wavefront sensing tasks in the weak atmospheric turbulence regime. However, in strong and deep turbulence situations, the complexity of a propagating wavefront increases significantly. Typically, beam breakup will happen and various portions of the beam will randomly interfere with each other. Consequently, some conventional techniques for wavefront sensing turn out to be inaccurate and misleading. For example, a Shack-Hartmann sensor will be confused by multi-spot/zero-spot result in some cells. The curvature sensor will be affected by random interference patterns for both the image acquired before the focal plane and the image acquired after the focal plane. We propose the use of a plenoptic sensor to solve complex wavefront sensing problems. In fact, our results show that even for multiple beams (their wavelengths can be the same) passing through the same turbulent channel, the plenoptic sensor can reconstruct the turbulence-induced distortion accurately. In this paper, we will demonstrate the plenoptic mapping principle to analyze and reconstruct the complex wavefront of a distorted laser beam.

pH Wave-Front Propagation in the Urea-Urease Reaction

PubMed Central

Wrobel, Magdalena M.; Bánsági, Tamás; Scott, Stephen K.; Taylor, Annette F.; Bounds, Chris O.; Carranza, Arturo; Pojman, John A.

2012-01-01

The urease-catalyzed hydrolysis of urea displays feedback that results in a switch from acid (pH ∼3) to base (pH ∼9) after a controllable period of time (from 10 to >5000 s). Here we show that the spatially distributed reaction can support pH wave fronts propagating with a speed of the order of 0.1−1 mm min−1. The experimental results were reproduced qualitatively in reaction-diffusion simulations including a Michaelis-Menten expression for the urease reaction with a bell-shaped rate-pH dependence. However, this model fails to predict that at lower enzyme concentrations, the unstirred reaction does not always support fronts when the well-stirred reaction still rapidly switches to high pH. PMID:22947878

Implementation of a rapid correction algorithm for adaptive optics using a plenoptic sensor

NASA Astrophysics Data System (ADS)

Ko, Jonathan; Wu, Chensheng; Davis, Christopher C.

2016-09-01

Adaptive optics relies on the accuracy and speed of a wavefront sensor in order to provide quick corrections to distortions in the optical system. In weaker cases of atmospheric turbulence often encountered in astronomical fields, a traditional Shack-Hartmann sensor has proved to be very effective. However, in cases of stronger atmospheric turbulence often encountered near the surface of the Earth, atmospheric turbulence no longer solely causes small tilts in the wavefront. Instead, lasers passing through strong or "deep" atmospheric turbulence encounter beam breakup, which results in interference effects and discontinuities in the incoming wavefront. In these situations, a Shack-Hartmann sensor can no longer effectively determine the shape of the incoming wavefront. We propose a wavefront reconstruction and correction algorithm based around the plenoptic sensor. The plenoptic sensor's design allows it to match and exceed the wavefront sensing capabilities of a Shack-Hartmann sensor for our application. Novel wavefront reconstruction algorithms can take advantage of the plenoptic sensor to provide a rapid wavefront reconstruction necessary for real time turbulence. To test the integrity of the plenoptic sensor and its reconstruction algorithms, we use artificially generated turbulence in a lab scale environment to simulate the structure and speed of outdoor atmospheric turbulence. By analyzing the performance of our system with and without the closed-loop plenoptic sensor adaptive optics system, we can show that the plenoptic sensor is effective in mitigating real time lab generated atmospheric turbulence.

Statistical virtual eye model based on wavefront aberration

PubMed Central

Wang, Jie-Mei; Liu, Chun-Ling; Luo, Yi-Ning; Liu, Yi-Guang; Hu, Bing-Jie

2012-01-01

Wavefront aberration affects the quality of retinal image directly. This paper reviews the representation and reconstruction of wavefront aberration, as well as the construction of virtual eye model based on Zernike polynomial coefficients. In addition, the promising prospect of virtual eye model is emphasized. PMID:23173112

Effect of DM Actuator Errors on the WFIRST/AFTA Coronagraph Contrast Performance

NASA Technical Reports Server (NTRS)

Sidick, Erkin; Shi, Fang

2015-01-01

The WFIRST/AFTA 2.4 m space telescope currently under study includes a stellar coronagraph for the imaging and the spectral characterization of extrasolar planets. The coronagraph employs two sequential deformable mirrors (DMs) to compensate for phase and amplitude errors in creating dark holes. DMs are critical elements in high contrast coronagraphs, requiring precision and stability measured in picometers to enable detection of Earth-like exoplanets. Working with a low-order wavefront-sensor the DM that is conjugate to a pupil can also be used to correct low-order wavefront drift during a scientific observation. However, not all actuators in a DM have the same gain. When using such a DM in low-order wavefront sensing and control subsystem, the actuator gain errors introduce high-spatial frequency errors to the DM surface and thus worsen the contrast performance of the coronagraph. We have investigated the effects of actuator gain errors and the actuator command digitization errors on the contrast performance of the coronagraph through modeling and simulations, and will present our results in this paper.

Comparison of Simulated Contrast Performance of Different Phase Induced Amplitude Apodization (PIAA) Coronagraph Configurations

NASA Technical Reports Server (NTRS)

Sidick, Erkin; Kern, Brian; Kuhnert, Andreas; Shaklan, Stuart

2013-01-01

We compare the broadband contrast performances of several Phase Induced Amplitude Apodization (PIAA) coronagraph configurations through modeling and simulations. The basic optical design of the PIAA coronagraph is the same as NASA's High Contrast Imaging Testbed (HCIT) setup at the Jet Propulsion Laboratory (JPL). Using a deformable mirror and a broadband wavefront sensing and control algorithm, we create a "dark hole" in the broadband point-spread function (PSF) with an inner working angle (IWA) of 2(f lambda/D)(sub sky). We evaluate two systems in parallel. One is a perfect system having a design PIAA output amplitude and not having any wavefront error at its exit-pupil. The other is a realistic system having a design PIAA output amplitude and the measured residual wavefront error. We also investigate the effect of Lyot stops of various sizes when a postapodizer is and is not present. Our simulations show that the best 7.5%-broadband contrast value achievable with the current PIAA coronagraph is approximately 1.5x10(exp -8).

WFIRST Coronagraph Technology Development Testbeds: Status and Recent Testbed Results

NASA Astrophysics Data System (ADS)

Shi, Fang; An, Xin; Balasubramanian, Kunjithapatham; cady, eric; Gordon, Brian; Greer, Frank; Kasdin, N. Jeremy; Kern, Brian; Lam, Raymond; Marx, David; Moody, Dwight; Patterson, Keith; Poberezhskiy, Ilya; mejia prada, camilo; Gersh-Range, Jessica; Eldorado Riggs, A. J.; Seo, Byoung-Joon; Shields, Joel; Sidick, Erkin; Tang, Hong; Trauger, John Terry; Truong, Tuan; White, Victor; Wilson, Daniel; Zhou, Hanying; JPL WFIRST Testbed Team, Princeton University

2018-01-01

As a part of technology development for the WFIRST coronagraph instrument (CGI), dedicated testbeds are built and commissioned at JPL. The coronagraph technology development testbeds include the Occulting Mask Coronagraph (OMC) testbed, the Shaped Pupil Coronagraph/Integral Field Spectrograph (SPC/IFS) testbed, and the Vacuum Surface Gauge (VSG) testbed. With its configuration similar to the WFIRST flight coronagraph instrument the OMC testbed consists of two coronagraph modes, Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC), a low order wavefront sensor (LOWFS), and an optical telescope assembly (OTA) simulator which can generate realistic LoS drift and jitter as well as low order wavefront error that would be induced by the WFIRST telescope’s vibration and thermal changes. The SPC/IFS testbed is a dedicated testbed to test the IFS working with a Shaped Pupil Coronagraph while the VSG testbed is for measuring and calibrating the deformable mirrors, a key component used for WFIRST CGI's wavefront control. In this poster, we will describe the testbed functions and status as well as the highlight of the latest testbed results from OMC, SPC/IFS and VSG testbeds.

Methods to Directly Image Exoplanets around Alpha Centauri and Other Multi-Star Systems

NASA Astrophysics Data System (ADS)

Belikov, R.; Sirbu, D.; Bendek, E.; Pluzhnik, E.

2017-12-01

The majority of FGK stars exist as multi-star star systems, and thus form a potentially rich target sample for direct imaging of exoplanets. A large fraction of these stars have starlight leakage from their companion that is brighter than rocky planets. This is in particular true of Alpha Centauri, which is 2.4x closer and about an order of magnitude brighter than any other FGK star, and thus may be the best target for any direct imaging mission, if the light of both stars can be suppressed. Thus, the ability to suppress starlight from two stars improves both the quantity and quality of Sun-like targets for missions such as WFIRST, LUVOIR, and HabEx. We present an analysis of starlight leak challenges in multi-star systems and techniques to solve those challenges, with an emphasis on imaging Alpha Centauri with WFIRST. For the case of internal coronagraphs, the fundamental problem appears to be independent wavefront control of multiple stars (at least if the companion is close enough or bright enough that it cannot simply be removed by longer exposure times or post-processing). We present a technique called Multi-Star Wavefront Control (MSWC) as a solution to this challenge and describe the results of our technology development program that advanced MSWC to TRL 3. Our program consisted of lab demonstrations of dark zones in two-star systems, validated simulations, as well as simulated predictions demonstrating that with this technology, contrasts needed for Earth-like planets are in principle achievable. We also demonstrate MSWC in Super-Nyquist mode, which allows suppression of multiple stars at separations greater than the spatial Nyquist limit of the deformable mirror.

Nonimaging speckle interferometry for high-speed nanometer-scale position detection.

PubMed

van Putten, E G; Lagendijk, A; Mosk, A P

2012-03-15

We experimentally demonstrate a nonimaging approach to displacement measurement for complex scattering materials. By spatially controlling the wavefront of the light that incidents on the material, we concentrate the scattered light in a focus on a designated position. This wavefront acts as a unique optical fingerprint that enables precise position detection of the illuminated material by simply measuring the intensity in the focus. By combining two fingerprints we demonstrate position detection along one in-plane dimension with a displacement resolution of 2.1 nm. As our approach does not require an image of the scattered field, it is possible to employ fast nonimaging detectors to enable high-speed position detection of scattering materials.

High resolution imaging and wavefront aberration correction in plenoptic systems.

PubMed

Trujillo-Sevilla, J M; Rodríguez-Ramos, L F; Montilla, I; Rodríguez-Ramos, J M

2014-09-01

Plenoptic imaging systems are becoming more common since they provide capabilities unattainable in conventional imaging systems, but one of their main limitations is the poor bidimensional resolution. Combining the wavefront phase measurement and the plenoptic image deconvolution, we propose a system capable of improving the resolution when a wavefront aberration is present and the image is blurred. In this work, a plenoptic system is simulated using Fourier optics, and the results show that an improved resolution is achieved, even in the presence of strong wavefront aberrations.

Shack-Hartmann wavefront sensor using a Raspberry Pi embedded system

NASA Astrophysics Data System (ADS)

Contreras-Martinez, Ramiro; Garduño-Mejía, Jesús; Rosete-Aguilar, Martha; Román-Moreno, Carlos J.

2017-05-01

In this work we present the design and manufacture of a compact Shack-Hartmann wavefront sensor using a Raspberry Pi and a microlens array. The main goal of this sensor is to recover the wavefront of a laser beam and to characterize its spatial phase using a simple and compact Raspberry Pi and the Raspberry Pi embedded camera. The recovery algorithm is based on a modified version of the Southwell method and was written in Python as well as its user interface. Experimental results and reconstructed wavefronts are presented.

Decomposition of the optical transfer function: wavefront coding imaging systems

NASA Astrophysics Data System (ADS)

Muyo, Gonzalo; Harvey, Andy R.

2005-10-01

We describe the mapping of the optical transfer function (OTF) of an incoherent imaging system into a geometrical representation. We show that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral. This representation provides a physical insight into the way in which wavefront coding can increase the depth of field of an imaging system and permits analytical quantification of salient OTF parameters, such as the depth of focus, the location of nulls, and amplitude and phase modulation of the wavefront-coding OTF.

Phase-preserving wavefront amplification at 590 nm by stimulated Raman scattering

NASA Astrophysics Data System (ADS)

Wick, D. V.; Gruneisen, M. T.; Peterson, P. R.

1998-03-01

This paper presents an experimental demonstration of high-gain optical-wavefront amplification by stimulated Raman scattering near the D 1 resonance in atomic sodium vapor. Single-pass weak-field gain of nearly 400 is achieved with only 800 mW of pump power. Through judicious focusing, the weak wavefront is confined to the central region of the focused pump wave where saturation of the dispersion profile minimizes phase distortions due to self-focusing effects. Phase-preserving amplification is demonstrated by interferometric measurements of an amplified TEM 00 wavefront.

Model wavefront sensor for adaptive confocal microscopy

NASA Astrophysics Data System (ADS)

Booth, Martin J.; Neil, Mark A. A.; Wilson, Tony

2000-05-01

A confocal microscope permits 3D imaging of volume objects by the inclusion of a pinhole in the detector path which eliminates out of focus light. This configuration is however very sensitive to aberrations induced by the specimen or the optical system and would therefore benefit from an adaptive optics approach. We present a wavefront sensor capable of measuring directly the Zernike components of an aberrated wavefront and show that it is particularly applicable to the confocal microscope since only those wavefronts originating in the focal region contribute to the measured aberration.

Shack-Hartmann wavefront-sensor-based adaptive optics system for multiphoton microscopy

PubMed Central

Cha, Jae Won; Ballesta, Jerome; So, Peter T.C.

2010-01-01

The imaging depth of two-photon excitation fluorescence microscopy is partly limited by the inhomogeneity of the refractive index in biological specimens. This inhomogeneity results in a distortion of the wavefront of the excitation light. This wavefront distortion results in image resolution degradation and lower signal level. Using an adaptive optics system consisting of a Shack-Hartmann wavefront sensor and a deformable mirror, wavefront distortion can be measured and corrected. With adaptive optics compensation, we demonstrate that the resolution and signal level can be better preserved at greater imaging depth in a variety of ex-vivo tissue specimens including mouse tongue muscle, heart muscle, and brain. However, for these highly scattering tissues, we find signal degradation due to scattering to be a more dominant factor than aberration. PMID:20799824

Measurement and comparison of the optical performance of an ophthalmic lens based on a Hartmann-Shack wavefront sensor in real viewing conditions.

PubMed

Zhou, Chuanqing; Wang, Weichao; Yang, Kun; Chai, Xinyu; Ren, Qiushi

2008-12-01

The spatially resolved wavefront aberrations of four types of ophthalmic lens are measured with a custom-built apparatus based on a Hartmann-Shack wavefront sensor and specially designed positioning stage. The wavefront aberrations of the progressive addition lenses (PALs) are compared. The results show that the distribution depends much on the design philosophy, although the average values of root mean square in the entire measurement areas have no significant difference. It is feasible to evaluate the optical performance through the wavefront analysis of PALs, but how to meet the customized visual needs of patients and how to minimize the unwanted aberrations in some special zones are important points that should be taken into account.

Shack-Hartmann wavefront-sensor-based adaptive optics system for multiphoton microscopy.

PubMed

Cha, Jae Won; Ballesta, Jerome; So, Peter T C

2010-01-01

The imaging depth of two-photon excitation fluorescence microscopy is partly limited by the inhomogeneity of the refractive index in biological specimens. This inhomogeneity results in a distortion of the wavefront of the excitation light. This wavefront distortion results in image resolution degradation and lower signal level. Using an adaptive optics system consisting of a Shack-Hartmann wavefront sensor and a deformable mirror, wavefront distortion can be measured and corrected. With adaptive optics compensation, we demonstrate that the resolution and signal level can be better preserved at greater imaging depth in a variety of ex-vivo tissue specimens including mouse tongue muscle, heart muscle, and brain. However, for these highly scattering tissues, we find signal degradation due to scattering to be a more dominant factor than aberration.

New derivation of the wavefront curvature transformation at an interface between two inhomogeneous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uzsin, B.

The principles for ray-tracing and wavefront curvature calculations in a three-dimensional medium are reviewed. A new derivation of the transformation of the wavefront curvature matrix at an interface between two inhomogeneous media is given. The derivation is based on a Taylor series expansion of the ray refraction equation at the interface between two inhomogeneous media, and only elementary geometric arguments are used. The wavefront curvature transformation at the interface is obtained by neglecting all terms in the direction of the surface normal. With proper definition of the variables, the derivation is also valid for a reflected wavefront. A simplified transformationmore » rule is derived for a reflected wave of the same type as the incident wave.« less

Multispectral Wavefronts Retrieval in Digital Holographic Three-Dimensional Imaging Spectrometry

NASA Astrophysics Data System (ADS)

Yoshimori, Kyu

2010-04-01

This paper deals with a recently developed passive interferometric technique for retrieving a set of spectral components of wavefronts that are propagating from a spatially incoherent, polychromatic object. The technique is based on measurement of 5-D spatial coherence function using a suitably designed interferometer. By applying signal processing, including aperture synthesis and spectral decomposition, one may obtains a set of wavefronts of different spectral bands. Since each wavefront is equivalent to the complex Fresnel hologram at a particular spectrum of the polychromatic object, application of the conventional Fresnel transform yields 3-D image of different spectrum. Thus, this technique of multispectral wavefronts retrieval provides a new type of 3-D imaging spectrometry based on a fully passive interferometry. Experimental results are also shown to demonstrate the validity of the method.

Extended use of two crossed Babinet compensators for wavefront sensing in adaptive optics

NASA Astrophysics Data System (ADS)

Paul, Lancelot; Kumar Saxena, Ajay

2010-12-01

An extended use of two crossed Babinet compensators as a wavefront sensor for adaptive optics applications is proposed. This method is based on the lateral shearing interferometry technique in two directions. A single record of the fringes in a pupil plane provides the information about the wavefront. The theoretical simulations based on this approach for various atmospheric conditions and other errors of optical surfaces are provided for better understanding of this method. Derivation of the results from a laboratory experiment using simulated atmospheric conditions demonstrates the steps involved in data analysis and wavefront evaluation. It is shown that this method has a higher degree of freedom in terms of subapertures and on the choice of detectors, and can be suitably adopted for real-time wavefront sensing for adaptive optics.

Zonal wavefront estimation using an array of hexagonal grating patterns

NASA Astrophysics Data System (ADS)

Pathak, Biswajit; Boruah, Bosanta R.

2014-10-01

Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during the estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.

The design of wavefront coded imaging system

NASA Astrophysics Data System (ADS)

Lan, Shun; Cen, Zhaofeng; Li, Xiaotong

2016-10-01

Wavefront Coding is a new method to extend the depth of field, which combines optical design and signal processing together. By using optical design software ZEMAX ,we designed a practical wavefront coded imaging system based on a conventional Cooke triplet system .Unlike conventional optical system, the wavefront of this new system is modulated by a specially designed phase mask, which makes the point spread function (PSF)of optical system not sensitive to defocus. Therefore, a series of same blurred images obtained at the image plane. In addition, the optical transfer function (OTF) of the wavefront coded imaging system is independent of focus, which is nearly constant with misfocus and has no regions of zeros. All object information can be completely recovered through digital filtering at different defocus positions. The focus invariance of MTF is selected as merit function in this design. And the coefficients of phase mask are set as optimization goals. Compared to conventional optical system, wavefront coded imaging system obtains better quality images under different object distances. Some deficiencies appear in the restored images due to the influence of digital filtering algorithm, which are also analyzed in this paper. The depth of field of the designed wavefront coded imaging system is about 28 times larger than initial optical system, while keeping higher optical power and resolution at the image plane.

The low-order wavefront control system for the PICTURE-C mission: high-speed image acquisition and processing

NASA Astrophysics Data System (ADS)

Hewawasam, Kuravi; Mendillo, Christopher B.; Howe, Glenn A.; Martel, Jason; Finn, Susanna C.; Cook, Timothy A.; Chakrabarti, Supriya

2017-09-01

The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The PICTURE-C low-order wavefront control (LOWC) system will be used to correct time-varying low-order aberrations due to pointing jitter, gravity sag, thermal deformation, and the gondola pendulum motion. We present the hardware and software implementation of the low-order ShackHartmann and reflective Lyot stop sensors. Development of the high-speed image acquisition and processing system is discussed with the emphasis on the reduction of hardware and computational latencies through the use of a real-time operating system and optimized data handling. By characterizing all of the LOWC latencies, we describe techniques to achieve a framerate of 200 Hz with a mean latency of ˜378 μs

Simultaneous generation of high-efficiency broadband asymmetric anomalous refraction and reflection waves with few-layer anisotropic metasurface

PubMed Central

Li, Zhancheng; Liu, Wenwei; Cheng, Hua; Liu, Jieying; Chen, Shuqi; Tian, Jianguo

2016-01-01

Optical metasurfaces consisting of single-layer nanostructures have immensely promising applications in wavefront control because they can be used to arbitrarily manipulate wave phase, and polarization. However, anomalous refraction and reflection waves have not yet been simultaneously and asymmetrically generated, and the limited efficiency and bandwidth of pre-existing single-layer metasurfaces hinder their practical applications. Here, a few-layer anisotropic metasurface is presented for simultaneously generating high-efficiency broadband asymmetric anomalous refraction and reflection waves. Moreover, the normal transmission and reflection waves are low and the anomalous waves are the predominant ones, which is quite beneficial for practical applications such as beam deflectors. Our work provides an effective method of enhancing the performance of anomalous wave generation, and the asymmetric performance of the proposed metasurface shows endless possibilities in wavefront control for nanophotonics device design and optical communication applications. PMID:27762286

Wavefront sensorless adaptive optics temporal focusing-based multiphoton microscopy

PubMed Central

Chang, Chia-Yuan; Cheng, Li-Chung; Su, Hung-Wei; Hu, Yvonne Yuling; Cho, Keng-Chi; Yen, Wei-Chung; Xu, Chris; Dong, Chen Yuan; Chen, Shean-Jen

2014-01-01

Temporal profile distortions reduce excitation efficiency and image quality in temporal focusing-based multiphoton microscopy. In order to compensate the distortions, a wavefront sensorless adaptive optics system (AOS) was integrated into the microscope. The feedback control signal of the AOS was acquired from local image intensity maximization via a hill-climbing algorithm. The control signal was then utilized to drive a deformable mirror in such a way as to eliminate the distortions. With the AOS correction, not only is the axial excitation symmetrically refocused, but the axial resolution with full two-photon excited fluorescence (TPEF) intensity is also maintained. Hence, the contrast of the TPEF image of a R6G-doped PMMA thin film is enhanced along with a 3.7-fold increase in intensity. Furthermore, the TPEF image quality of 1μm fluorescent beads sealed in agarose gel at different depths is improved. PMID:24940539

Active wavefront control challenges of the NASA Large Deployable Reflector (LDR)

NASA Technical Reports Server (NTRS)

Meinel, Aden B.; Meinel, Marjorie P.; Manhart, Paul K.; Hochberg, Eric B.

1989-01-01

The 20-m Large Deployable Reflector will have a segmented primary mirror. Achieving diffraction-limited performance at 50 microns requires correction for the errors of tilt and piston of the primary mirror. This correction can be obtained in two ways, the use of an active primary or a correction at a demagnified pupil of the primary. A critical requirement is the means for measurement of the wavefront error and maintaining phasing during the observation of objects that may be too faint for determining the error. Absolute phasing can only be determined using a cooperative source. Maintenance of phasing can be done with an on-board source. A number of options are being explored as discussed below. The many issues concerning the assessment and control of an active segmented mirror will be addressed with an early construction of the Precision Segmented Reflector testbed.

Active wavefront control challenges of the NASA Large Deployable Reflector (LDR)

NASA Astrophysics Data System (ADS)

Meinel, Aden B.; Meinel, Marjorie P.; Manhart, Paul K.; Hochberg, Eric B.

1989-09-01

The 20-m Large Deployable Reflector will have a segmented primary mirror. Achieving diffraction-limited performance at 50 microns requires correction for the errors of tilt and piston of the primary mirror. This correction can be obtained in two ways, the use of an active primary or a correction at a demagnified pupil of the primary. A critical requirement is the means for measurement of the wavefront error and maintaining phasing during the observation of objects that may be too faint for determining the error. Absolute phasing can only be determined using a cooperative source. Maintenance of phasing can be done with an on-board source. A number of options are being explored as discussed below. The many issues concerning the assessment and control of an active segmented mirror will be addressed with an early construction of the Precision Segmented Reflector testbed.

Kilohertz binary phase modulator for pulsed laser sources using a digital micromirror device.

PubMed

Hoffmann, Maximilian; Papadopoulos, Ioannis N; Judkewitz, Benjamin

2018-01-01

The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation, or patterned photostimulation. For most of these applications, it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy. Here we introduce a DMD-based optical design that overcomes these limitations and achieves dispersion-free high-speed binary phase modulation. We show that this phase modulation can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.

Kilohertz binary phase modulator for pulsed laser sources using a digital micromirror device

NASA Astrophysics Data System (ADS)

Hoffmann, Maximilian; Papadopoulos, Ioannis N.; Judkewitz, Benjamin

2018-01-01

The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation or patterned photostimulation. For most of these applications it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator, but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy. Here we introduce a DMD-based optical design that overcomes these limitations and achieves dispersion-free high-speed binary phase modulation. We show that this phase modulation can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.

An adaptive optics package designed for astronomical use with a laser guide star tuned to an absorption line of atomic sodium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salmon, J.T.; Avicola, K.; Brase, J.M.

1994-04-11

We present the design and implementation of a very compact adaptive optic system that senses the return light from a sodium guide-star and controls a deformable mirror and a pointing mirror to compensate atmospheric perturbations in the wavefront. The deformable mirror has 19 electrostrictive actuators and triangular subapertures. The wavefront sensor is a Hartmann sensor with lenslets on triangular centers. The high-bandwidth steering mirror assembly incorporates an analog controller that samples the tilt with an avalanche photodiode quad cell. An {line_integral}/25 imaging leg focuses the light into a science camera that can either obtain long-exposure images or speckle data. Inmore » laboratory tests overall Strehl ratios were improved by a factor of 3 when a mylar sheet was used as an aberrator. The crossover frequency at unity gain is 30 Hz.« less

Wavefront tilt feedforward for the formation interferometer testbad (FIT)

NASA Technical Reports Server (NTRS)

Shields, J. F.; Liewer, K.; Wehmeier, U.

2002-01-01

Separated spacecraft interferometry is a candidate architecture for several future NASA missions. The Formation Interferometer Testbed (FIT) is a ground based testbed dedicated to the validation of this key technology for a formation of two spacecraft. In separated spacecraft interferometry, the residual relative motion of the component spacecraft must be compensated for by articulation of the optical components. In this paper, the design of the FIT interferometer pointing control system is described. This control system is composed of a metrology pointing loop that maintains an optical link between the two spacecraft and two stellar pointing loops for stabilizing the stellar wavefront at both the right and left apertures of the instrument. A novel feedforward algorithm is used to decouple the metrology loop from the left side stellar loop. Experimental results from the testbed are presented that verify this approach and that fully demonstrate the performance of the algorithm.

TECHNIQUES FOR HIGH-CONTRAST IMAGING IN MULTI-STAR SYSTEMS. I. SUPER-NYQUIST WAVEFRONT CONTROL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, S.; Belikov, R.; Bendek, E.

2015-09-01

Direct imaging of extra-solar planets is now a reality with the deployment and commissioning of the first generation of specialized ground-based instruments (GPI, SPHERE, P1640, and SCExAO). These systems allow of planets 10{sup 7} times fainter than their host star. For space-based missions (EXCEDE, EXO-C, EXO-S, WFIRST), various teams have demonstrated laboratory contrasts reaching 10{sup −10} within a few diffraction limits from the star. However, all of these current and future systems are designed to detect faint planets around a single host star, while most non-M-dwarf stars such as Alpha Centauri belong to multi-star systems. Direct imaging around binaries/multiple systemsmore » at a level of contrast allowing detection of Earth-like planets is challenging because the region of interest is contaminated by the host star's companion in addition to the host itself. Generally, the light leakage is caused by both diffraction and aberrations in the system. Moreover, the region of interest usually falls outside the correcting zone of the deformable mirror (DM) with respect to the companion. Until now, it has been thought that removing the light of a companion star is too challenging, leading to the exclusion of many binary systems from target lists of direct imaging coronographic missions. In this paper, we will show new techniques for high-contrast imaging of planets around multi-star systems and detail the Super-Nyquist Wavefront Control (SNWC) method, which allows wavefront errors to be controlled beyond the nominal control region of the DM. Our simulations have demonstrated that, with SNWC, raw contrasts of at least 5 × 10{sup −9} in a 10% bandwidth are possible.« less

Absolute color scale for improved diagnostics with wavefront error mapping.

PubMed

Smolek, Michael K; Klyce, Stephen D

2007-11-01

Wavefront data are expressed in micrometers and referenced to the pupil plane, but current methods to map wavefront error lack standardization. Many use normalized or floating scales that may confuse the user by generating ambiguous, noisy, or varying information. An absolute scale that combines consistent clinical information with statistical relevance is needed for wavefront error mapping. The color contours should correspond better to current corneal topography standards to improve clinical interpretation. Retrospective analysis of wavefront error data. Historic ophthalmic medical records. Topographic modeling system topographical examinations of 120 corneas across 12 categories were used. Corneal wavefront error data in micrometers from each topography map were extracted at 8 Zernike polynomial orders and for 3 pupil diameters expressed in millimeters (3, 5, and 7 mm). Both total aberrations (orders 2 through 8) and higher-order aberrations (orders 3 through 8) were expressed in the form of frequency histograms to determine the working range of the scale across all categories. The standard deviation of the mean error of normal corneas determined the map contour resolution. Map colors were based on corneal topography color standards and on the ability to distinguish adjacent color contours through contrast. Higher-order and total wavefront error contour maps for different corneal conditions. An absolute color scale was produced that encompassed a range of +/-6.5 microm and a contour interval of 0.5 microm. All aberrations in the categorical database were plotted with no loss of clinical information necessary for classification. In the few instances where mapped information was beyond the range of the scale, the type and severity of aberration remained legible. When wavefront data are expressed in micrometers, this absolute scale facilitates the determination of the severity of aberrations present compared with a floating scale, particularly for distinguishing normal from abnormal levels of wavefront error. The new color palette makes it easier to identify disorders. The corneal mapping method can be extended to mapping whole eye wavefront errors. When refraction data are expressed in diopters, the previously published corneal topography scale is suggested.

Terahertz beam switching by electrical control of graphene-enabled tunable metasurface.

PubMed

Zhang, Yin; Feng, Yijun; Zhao, Junming; Jiang, Tian; Zhu, Bo

2017-10-26

Controlling the terahertz wave, especially the dynamical and full control of terahertz wavefront, is highly demanded due to the increasing development of practical devices and application systems. Recently considerable efforts have been made to fill the 'terahertz gap' with the help of artificial metamaterial or metasurface incorporated with graphene material. Here, we propose a scheme to design tunable metasurface consisting of metallic patch array on a grounded polymer substrate embedded with graphene layers to electrically control the electromagnetic beam reflection at terahertz frequency. By adjusting geometric dimension of the patch elements, 360 degree reflection phase range may be achieved, thus abrupt phase shifts can be introduced along the metasurface for tailoring the reflected wavefront. Moreover, the reflective phase gradient over the metasurface can be switched between 90 and 360 degree by controlling the Fermi energy of the embedded graphene through voltage biasing, hence dynamically switching the reflective beam directions. Numerical simulations demonstrate that either single beam or dual beam dynamically switching between normal and oblique reflection angles can be well attained at working frequency. The proposed approach will bring much freedom in the design of beam manipulation devices and may be applied to terahertz radiation control.

Aspheric versus wavefront-guided aspheric photorefractive keratectomy in eyes with significant astigmatism.

PubMed

Faramarzi, Amir; Moshirfar, Majid; Karimian, Farid; Delfazayebaher, Siamak; Kheiri, Bahareh

2017-12-01

To compare the refractive and higher-order aberrations (HOAs) outcomes after photorefractive keratectomy (PRK) in patients with significant astigmatism using aspheric versus wavefront-guided aspheric profiles. Ophthalmic Research Center and Department of Ophthalmology, Shahid Beheshti University of Medical Sciences, Negah Eye Hospital, Tehran, Iran. Prospective randomized case series. One eye of each patient with a refractive astigmatism more than 2.00 diopters (D) randomly received aspheric PRK. In the other eye, wavefront-guided and aspheric treatment was performed using a personalized treatment advanced algorithm. Visual acuity, refractive errors, and HOAs were compared between the 2 groups preoperatively and 12 months postoperatively. The study comprised 32 patients (64 eyes). The mean preoperative refractive astigmatism was -4.07 D ± 1.64 (SD) and -4.02 ± 1.55 D in the aspheric group and wavefront-guided aspheric group, respectively (P = .2). The mean postoperative astigmatism was -0.46 ± 0.37 D and -0.82 ± 0.53 D in the aspheric group and wavefront-guided aspheric group, respectively (P = .02). Postoperatively, the root mean square of total HOAs was significantly increased in both groups. However, compared with wavefront-guided aspheric PRK, aspheric PRK induced fewer HOAs (P = .003). In eyes with high astigmatism, post-PRK residual astigmatism was lower in the aspheric group than in the wavefront-guided aspheric group. The increase in HOAs was significantly higher in the wavefront-guided aspheric group than in the aspheric group. Copyright © 2017 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

An Optical Wavefront Sensor Based on a Double Layer Microlens Array

PubMed Central

Lin, Vinna; Wei, Hsiang-Chun; Hsieh, Hsin-Ta; Su, Guo-Dung John

2011-01-01

In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA) to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS) above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin), the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution. PMID:22346643

Wavefront-guided correction of ocular aberrations: Are phase plate and refractive surgery solutions equal?

NASA Astrophysics Data System (ADS)

Marchese, Linda E.; Munger, Rejean; Priest, David

2005-08-01

Wavefront-guided laser eye surgery has been recently introduced and holds the promise of correcting not only defocus and astigmatism in patients but also higher-order aberrations. Research is just beginning on the implementation of wavefront-guided methods in optical solutions, such as phase-plate-based spectacles, as alternatives to surgery. We investigate the theoretical differences between the implementation of wavefront-guided surgical and phase plate corrections. The residual aberrations of 43 model eyes are calculated after simulated refractive surgery and also after a phase plate is placed in front of the untreated eye. In each case, the current wavefront-guided paradigm that applies a direct map of the ocular aberrations to the correction zone is used. The simulation results demonstrate that an ablation map that is a Zernike fit of a direct transform of the ocular wavefront phase error is not as efficient in correcting refractive errors of sphere, cylinder, spherical aberration, and coma as when the same Zernike coefficients are applied to a phase plate, with statistically significant improvements from 2% to 6%.

Wavefront measurement of plastic lenses for mobile-phone applications

NASA Astrophysics Data System (ADS)

Huang, Li-Ting; Cheng, Yuan-Chieh; Wang, Chung-Yen; Wang, Pei-Jen

2016-08-01

In camera lenses for mobile-phone applications, all lens elements have been designed with aspheric surfaces because of the requirements in minimal total track length of the lenses. Due to the diffraction-limited optics design with precision assembly procedures, element inspection and lens performance measurement have become cumbersome in the production of mobile-phone cameras. Recently, wavefront measurements based on Shack-Hartmann sensors have been successfully implemented on injection-molded plastic lens with aspheric surfaces. However, the applications of wavefront measurement on small-sized plastic lenses have yet to be studied both theoretically and experimentally. In this paper, both an in-house-built and a commercial wavefront measurement system configured on two optics structures have been investigated with measurement of wavefront aberrations on two lens elements from a mobile-phone camera. First, the wet-cell method has been employed for verifications of aberrations due to residual birefringence in an injection-molded lens. Then, two lens elements of a mobile-phone camera with large positive and negative power have been measured with aberrations expressed in Zernike polynomial to illustrate the effectiveness in wavefront measurement for troubleshooting defects in optical performance.

Longitudinal measurements of luminance and chromatic contrast sensitivity: comparison between wavefront-guided LASIK and contralateral PRK for myopia.

PubMed

Barboni, Mirella Telles Salgueiro; Feitosa-Santana, Claudia; Barreto Junior, Jackson; Lago, Marcos; Bechara, Samir Jacob; Alves, Milton Ruiz; Ventura, Dora Fix

2013-10-01

The present study aimed to compare the postoperative contrast sensitivity functions between wavefront-guided LASIK eyes and their contralateral wavefront-guided PRK eyes. The participants were 11 healthy subjects (mean age=32.4 ± 6.2 years) who had myopic astigmatism. The spatial contrast sensitivity functions were measured before and three times after the surgery. Psycho and a Cambridge graphic board (VSG 2/4) were used to measure luminance, red-green, and blue-yellow spatial contrast sensitivity functions (from 0.85 to 13.1 cycles/degree). Longitudinal analysis and comparison between surgeries were performed. There was no significant contrast sensitivity change during the one-year follow-up measurements neither for LASIK nor for PRK eyes. The comparison between procedures showed no differences at 12 months postoperative. The present data showed similar contrast sensitivities during one-year follow-up of wave-front guided refractive surgeries. Moreover, one year postoperative data showed no differences in the effects of either wavefront-guided LASIK or wavefront-guided PRK on the luminance and chromatic spatial contrast sensitivity functions.

Direct-Solve Image-Based Wavefront Sensing

NASA Technical Reports Server (NTRS)

Lyon, Richard G.

2009-01-01

A method of wavefront sensing (more precisely characterized as a method of determining the deviation of a wavefront from a nominal figure) has been invented as an improved means of assessing the performance of an optical system as affected by such imperfections as misalignments, design errors, and fabrication errors. The method is implemented by software running on a single-processor computer that is connected, via a suitable interface, to the image sensor (typically, a charge-coupled device) in the system under test. The software collects a digitized single image from the image sensor. The image is displayed on a computer monitor. The software directly solves for the wavefront in a time interval of a fraction of a second. A picture of the wavefront is displayed. The solution process involves, among other things, fast Fourier transforms. It has been reported to the effect that some measure of the wavefront is decomposed into modes of the optical system under test, but it has not been reported whether this decomposition is postprocessing of the solution or part of the solution process.

Transmitted wavefront testing with large dynamic range based on computer-aided deflectometry

NASA Astrophysics Data System (ADS)

Wang, Daodang; Xu, Ping; Gong, Zhidong; Xie, Zhongmin; Liang, Rongguang; Xu, Xinke; Kong, Ming; Zhao, Jun

2018-06-01

The transmitted wavefront testing technique is demanded for the performance evaluation of transmission optics and transparent glass, in which the achievable dynamic range is a key issue. A computer-aided deflectometric testing method with fringe projection is proposed for the accurate testing of transmitted wavefronts with a large dynamic range. Ray tracing of the modeled testing system is carried out to achieve the virtual ‘null’ testing of transmitted wavefront aberrations. The ray aberration is obtained from the ray tracing result and measured slope, with which the test wavefront aberration can be reconstructed. To eliminate testing system modeling errors, a system geometry calibration based on computer-aided reverse optimization is applied to realize accurate testing. Both numerical simulation and experiments have been carried out to demonstrate the feasibility and high accuracy of the proposed testing method. The proposed testing method can achieve a large dynamic range compared with the interferometric method, providing a simple, low-cost and accurate way for the testing of transmitted wavefronts from various kinds of optics and a large amount of industrial transmission elements.

Calibrating the interaction matrix for the LINC-NIRVANA high layer wavefront sensor.

PubMed

Zhang, Xianyu; Arcidiacono, Carmelo; Conrad, Albert R; Herbst, Thomas M; Gaessler, Wolfgang; Bertram, Thomas; Ragazzoni, Roberto; Schreiber, Laura; Diolaiti, Emiliano; Kuerster, Martin; Bizenberger, Peter; Meschke, Daniel; Rix, Hans-Walter; Rao, Changhui; Mohr, Lars; Briegel, Florian; Kittmann, Frank; Berwein, Juergen; Trowitzsch, Jan

2012-03-26

LINC-NIRVANA is a near-infrared Fizeau interferometric imager that will operate at the Large Binocular Telescope. In preparation for the commissioning of this instrument, we conducted experiments for calibrating the high-layer wavefront sensor of the layer-oriented multi-conjugate adaptive optics system. For calibrating the multi-pyramid wavefront sensor, four light sources were used to simulate guide stars. Using this setup, we developed the push-pull method for calibrating the interaction matrix. The benefits of this method over the traditional push-only method are quantified, and also the effects of varying the number of push-pull frames over which aberrations are averaged is reported. Finally, we discuss a method for measuring mis-conjugation between the deformable mirror and the wavefront sensor, and the proper positioning of the wavefront sensor detector with respect to the four pupil positions.

Three-dimensional spatiotemporal pulse characterization with an acousto-optic pulse shaper and a Hartmann-Shack wavefront sensor.

PubMed

Cousin, Seth L; Bueno, Juan M; Forget, Nicolas; Austin, Dane R; Biegert, J

2012-08-01

We demonstrate a simplified arrangement for spatiotemporal ultrashort pulse characterization called Hartmann-Shack assisted, multidimensional, shaper-based technique for electric-field reconstruction. It employs an acousto-optic pulse shaper in combination with a second-order nonlinear crystal and a Hartmann-Shack wavefront sensor. The shaper is used as a tunable bandpass filter, and the wavefronts and intensities of quasimonochromatic spectral slices of the pulse are obtained using the Hartmann-Shack wavefront sensor. The wavefronts and intensities of the spectral slices are related to one another using shaper-assisted frequency-resolved optical gating measurements, performed at particular points in the beam. This enables a three-dimensional reconstruction of the amplitude and phase of the pulse. We present some example pulse measurements and discuss the operating parameters of the device.

Evaluation of anterior lenticonus in alport syndrome using tracey wavefront aberrometry and transmission electron microscopy.

PubMed

Kim, Kwan Soo; Kim, Mo Sae; Kim, Joon Mo; Choi, Chul Young

2010-01-01

To evaluate the efficacy of Tracey wavefront aberrometry (Tracey Technologies, Houston, TX) and transmission electron microscopy for the detection of anterior lenticonus in Alport syndrome. Tracey wavefront aberrometry was used to treat a patient with bilateral anterior lenticonus who had a history of Alport syndrome. For transmission electron microscopic examination, anterior lens capsules were obtained during clear lens phacoemulsification and intraocular lens implantation. Spherical aberrations were the predominant higher-order aberrations in the internal optics of both eyes. The Tracey wavefront aberrometer showed that most of the irregular astigmatism originated from the lenticular portion. Transmission electron microscopy of the specimens showed anterior lens capsules with decreased thickness and multiple dehiscences. Tracey wavefront aberrometry and transmission electron microscopy are effective tools for evaluation of anterior lenticonus in Alport syndrome. Copyright 2010, SLACK Incorporated.

Zonal wavefront estimation using an array of hexagonal grating patterns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pathak, Biswajit, E-mail: b.pathak@iitg.ernet.in, E-mail: brboruah@iitg.ernet.in; Boruah, Bosanta R., E-mail: b.pathak@iitg.ernet.in, E-mail: brboruah@iitg.ernet.in

2014-10-15

Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during themore » estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.« less

Technology Advancement of the Visible Nulling Coronagraph

NASA Technical Reports Server (NTRS)

Lyon, Richard G.; Clampin, Mark; Petrone, Peter; Thompson, Patrick; Bolcar, Matt; Madison, Timothy; Woodruff, Robert; Noecker, Charley; Kendrick, Steve

2010-01-01

The critical high contrast imaging technology for the Extrasolar Planetary Imaging Coronagraph (EPIC) mission concept is the visible nulling coronagraph (VNC). EPIC would be capable of imaging jovian planets, dust/debris disks, and potentially super-Earths and contribute to answering how bright the debris disks are for candidate stars. The contrast requirement for EPIC is 10(exp 9) contrast at 125 milli-arseconds inner working angle. To advance the VNC technology NASA/Goddard Space Flight Center, in collaboration with Lockheed-Martin, previously developed a vacuum VNC testbed, and achieved narrowband and broadband suppression of the core of the Airy disk. Recently our group was awarded a NASA Technology Development for Exoplanet Missions to achieve two milestones: (i) 10(exp 8) contrast in narrowband light, and, (ii) 10(ecp 9) contrast in broader band light; one milestone per year, and both at 2 Lambda/D inner working angle. These will be achieved with our 2nd generation testbed known as the visible nulling testbed (VNT). It contains a MEMS based hex-packed segmented deformable mirror known as the multiple mirror array (MMA) and coherent fiber bundle, i.e. a spatial filter array (SFA). The MMA is in one interferometric arm and works to set the wavefront differences between the arms to zero. Each of the MMA segments is optically mapped to a single mode fiber of the SFA, and the SFA passively cleans the sub-aperture wavefront error leaving only piston, tip and tilt error to be controlled. The piston degree of freedom on each segment is used to correct the wavefront errors, while the tip/tilt is used to simultaneously correct the amplitude errors. Thus the VNT controls both amplitude and wavefront errors with a single MMA in closed-loop in a vacuum tank at approx.20 Hz. Herein we will discuss our ongoing progress with the VNT.

Development of a Pyramid Wave-front Sensor

NASA Astrophysics Data System (ADS)

El Hadi, Kacem; Vignaux, Mael; Fusco, Thierry

2013-12-01

Within the framework of the E-ELT studies, several laboratories are involved on some instruments: HARMONY with its ATLAS adaptive optics [AO] system, EAGLE or EPICS. Most of the AO systems will probably integrate one or several pyramidal wavefront sensors, PWFS (R. Ragazzoni [1]). The coupling in an AO loop and the control in laboratory (then on sky) of this type of sensor is fundamental for the continuation of the projects related to OA systems on the E-ELT. LAM (Laboratory of Astrophysics of Marseille) is involved in particular in the VLT-SPHERE, ATLAS, EPICS projects. For the last few years, our laboratory has been carrying out different R&D activities in AO instrumentation for ELTs. An experimental AO bench is designed and being developed to allow the validation of new wave-front sensing and control concepts [2]. One the objectives of this bench, is the experimental validation of a pyramid WFS. Theoretical investigations on its behavior have been already made. The world's fastest and most sensitive camera system (OCAM2) has been recently developed at LAM (J.L Gach [3], First Light Imaging). Conjugating this advantage with the pyramid concept, we plan to demonstrate a home made Pyramid sensor for Adaptive Optics whose the speed and the precision are the key points. As a joint collaboration with ONERA and Shaktiware, our work aims at the optimization (measurement process, calibration and operation) in laboratory then on the sky of a pyramid sensor dedicated to the first generation instruments for ELTs. The sensor will be implemented on the ONERA ODISSEE AO bench combining thus a pyramid and a Shack-Hartmann wavefront sensors. What would give the possibility to compare strictly these two WFS types and make this bench unique in France and even in Europe. Experimental work on laboratory demonstration is undergoing. The status of our development will presented at the conference.

Ocular wavefront aberrations in the common marmoset Callithrix jacchus: effects of age and refractive error

PubMed Central

Coletta, Nancy J.; Marcos, Susana; Troilo, David

2012-01-01

The common marmoset, Callithrix jacchus, is a primate model for emmetropization studies. The refractive development of the marmoset eye depends on visual experience, so knowledge of the optical quality of the eye is valuable. We report on the wavefront aberrations of the marmoset eye, measured with a clinical Hartmann-Shack aberrometer (COAS, AMO Wavefront Sciences). Aberrations were measured on both eyes of 23 marmosets whose ages ranged from 18 to 452 days. Twenty-one of the subjects were members of studies of emmetropization and accommodation, and two were untreated normal subjects. Eleven of the 21 experimental subjects had worn monocular diffusers or occluders and ten had worn binocular spectacle lenses of equal power. Monocular deprivation or lens rearing began at about 45 days of age and ended at about 108 days of age. All refractions and aberration measures were performed while the eyes were cyclopleged; most aberration measures were made while subjects were awake, but some control measurements were performed under anesthesia. Wavefront error was expressed as a seventh-order Zernike polynomial expansion, using the Optical Society of America’s naming convention. Aberrations in young marmosets decreased up to about 100 days of age, after which the higher-order RMS aberration leveled off to about 0.10 micron over a 3 mm diameter pupil. Higher-order aberrations were 1.8 times greater when the subjects were under general anesthesia than when they were awake. Young marmoset eyes were characterized by negative spherical aberration. Visually deprived eyes of the monocular deprivation animals had greater wavefront aberrations than their fellow untreated eyes, particularly for asymmetric aberrations in the odd-numbered Zernike orders. Both lens-treated and deprived eyes showed similar significant increases in Z3-3 trefoil aberration, suggesting the increase in trefoil may be related to factors that do not involve visual feedback. PMID:20800078

Development of a wavefront sensor for terahertz pulses.

PubMed

Abraham, Emmanuel; Cahyadi, Harsono; Brossard, Mathilde; Degert, Jérôme; Freysz, Eric; Yasui, Takeshi

2016-03-07

Wavefront characterization of terahertz pulses is essential to optimize far-field intensity distribution of time-domain (imaging) spectrometers or increase the peak power of intense terahertz sources. In this paper, we report on the wavefront measurement of terahertz pulses using a Hartmann sensor associated with a 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. We quantitatively determined the deformations of planar and converging spherical wavefronts using the modal Zernike reconstruction least-squares method. Associated with deformable mirrors, the sensor will also open the route to terahertz adaptive optics.

Wavefront reconstruction from non-modulated pyramid wavefront sensor data using a singular value type expansion

NASA Astrophysics Data System (ADS)

Hutterer, Victoria; Ramlau, Ronny

2018-03-01

The new generation of extremely large telescopes includes adaptive optics systems to correct for atmospheric blurring. In this paper, we present a new method of wavefront reconstruction from non-modulated pyramid wavefront sensor data. The approach is based on a simplified sensor model represented as the finite Hilbert transform of the incoming phase. Due to the non-compactness of the finite Hilbert transform operator the classical theory for singular systems is not applicable. Nevertheless, we can express the Moore-Penrose inverse as a singular value type expansion with weighted Chebychev polynomials.

x-y curvature wavefront sensor.

PubMed

Cagigal, Manuel P; Valle, Pedro J

2015-04-15

In this Letter, we propose a new curvature wavefront sensor based on the principles of optical differentiation. The theoretically modeled setup consists of a diffractive optical mask placed at the intermediate plane of a classical two-lens coherent optical processor. The resulting image is composed of a number of local derivatives of the entrance pupil function whose proper combination provides the wavefront curvature. In contrast to the common radial curvature sensors, this one is able to provide the x and y wavefront curvature maps simultaneously. The sensor offers other additional advantages like having high spatial resolution, adjustable dynamic range, and not being sensitive to misalignment.

Wavefront-sensor-based electron density measurements for laser-plasma accelerators.

PubMed

Plateau, G R; Matlis, N H; Geddes, C G R; Gonsalves, A J; Shiraishi, S; Lin, C; van Mourik, R A; Leemans, W P

2010-03-01

Characterization of the electron density in laser produced plasmas is presented using direct wavefront analysis of a probe laser beam. The performance of a laser-driven plasma-wakefield accelerator depends on the plasma wavelength and hence on the electron density. Density measurements using a conventional folded-wave interferometer and using a commercial wavefront sensor are compared for different regimes of the laser-plasma accelerator. It is shown that direct wavefront measurements agree with interferometric measurements and, because of the robustness of the compact commercial device, offer greater phase sensitivity and straightforward analysis, improving shot-to-shot plasma density diagnostics.

Comparison between non-modulation four-sided and two-sided pyramid wavefront sensor.

PubMed

Wang, Jianxin; Bai, Fuzhong; Ning, Yu; Huang, Linhai; Wang, Shengqian

2010-12-20

Based on the diffraction theory the paper analyzes non-modulation Pyramid wavefront sensor (PWFS, namely, four-sided pyramid) and two-sided pyramid wavefront sensor (TSPWFS), and expresses the detected signals as a function of the measured wavefront. The expressions of the detected signals show that non-modulation PWFS and TSPWFS hold the same properties of both slope and direct phase sensors. We compare both sensors working in slope and phase sensing by theory and numerical simulations. The results demonstrate that the performance of TSPWFS excels that of PWFS. Additionally, the influence of interference between adjacent pupils is discussed.

NGS2: a focal plane array upgrade for the GeMS multiple tip-tilt wavefront sensor

NASA Astrophysics Data System (ADS)

Rigaut, François; Price, Ian; d'Orgeville, Céline; Bennet, Francis; Herrald, Nick; Paulin, Nicolas; Uhlendorf, Kristina; Garrel, Vincent; Sivo, Gaetano; Montes, Vanessa; Trujillo, Chad

2016-07-01

NGS2 is an upgrade for the multi-natural guide star tip-tilt & plate scale wavefront sensor for GeMS (Gemini Multi-Conjugate Adaptive Optics system). It uses a single Nüvü HNü-512 Electron-Multiplied CCD array that spans the entire GeMS wavefront sensor focal plane. Multiple small regions-of-interest are used to enable frame rates up to 800Hz. This set up will improve the optical throughput with respect to the current wavefront sensor, as well as streamline acquisition and allow for distortion compensation.

Wavefront-sensor-based electron density measurements for laser-plasma accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plateau, Guillaume; Matlis, Nicholas; Geddes, Cameron

2010-02-20

Characterization of the electron density in laser produced plasmas is presented using direct wavefront analysis of a probe laser beam. The performance of a laser-driven plasma-wakefield accelerator depends on the plasma wavelength, hence on the electron density. Density measurements using a conventional folded-wave interferometer and using a commercial wavefront sensor are compared for different regimes of the laser-plasma accelerator. It is shown that direct wavefront measurements agree with interferometric measurements and, because of the robustness of the compact commercial device, have greater phase sensitivity, straightforward analysis, improving shot-to-shot plasma-density diagnostics.

Partially coherent wavefront propagation simulations: Mirror and monochromator crystal quality assessment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiegart, L., E-mail: lwiegart@bnl.gov; Fluerasu, A.; Chubar, O.

2016-07-27

We have applied fully-and partially-coherent synchrotron radiation wavefront propagation simulations, implemented in the “Synchrotron Radiation Workshop” (SRW) computer code, to analyse the effects of imperfect mirrors and monochromator at the Coherent Hard X-ray beamline. This beamline is designed for X-ray Photon Correlation Spectroscopy, a technique that heavily relies on the partial coherence of the X-ray beam and benefits from a careful preservation of the X-ray wavefront. We present simulations and a comparison with the measured beam profile at the sample position, which show the impact of imperfect optics on the wavefront.

Update on laser vision correction using wavefront analysis with the CustomCornea system and LADARVision 193-nm excimer laser

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; McDonald, Marguerite B.; Pettit, George H.; Papaioannou, Thanassis; Grundfest, Warren S.

2002-06-01

A study was undertaken to assess whether results of laser vision correction with the LADARVISION 193-nm excimer laser (Alcon-Autonomous technologies) can be improved with the use of wavefront analysis generated by a proprietary system including a Hartman-Schack sensor and expressed using Zernicke polynomials. A total of 82 eyes underwent LASIK in several centers with an improved algorithm, using the CustomCornea system. A subgroup of 48 eyes of 24 patients was randomized so that one eye undergoes conventional treatment and one eye undergoes treatment based on wavefront analysis. Treatment parameters were equal for each type of refractive error. 83% of all eyes had uncorrected vision of 20/20 or better and 95% were 20/25 or better. In all groups, uncorrected visual acuities did not improve significantly in eyes treated with wavefront analysis compared to conventional treatments. Higher order aberrations were consistently better corrected in eyes undergoing treatment based on wavefront analysis for LASIK at 6 months postop. In addition, the number of eyes with reduced RMS was significantly higher in the subset of eyes treated with a wavefront algorithm (38% vs. 5%). Wavefront technology may improve the outcomes of laser vision correction with the LADARVISION excimer laser. Further refinements of the technology and clinical trials will contribute to this goal.

The CAFADIS camera: a new tomographic wavefront sensor for Adaptive Optics

NASA Astrophysics Data System (ADS)

Rodríguez, J. M.; Femenía, B.; Montilla, I.; Rodríguez-Ramos, L. F.; Marichal-Hernández, J. G.; Lüke, J. P.; López, R.; Díaz, J. J.; Martín, Y.

The CAFADIS camera is a new wavefront sensor (WFS) patented by the Universidad de La Laguna. CAFADIS is a system based on the concept of plenoptic camera originally proposed by Adelson and Wang [Single lens stereo with a plenoptic camera, IEEE Transactions on Pattern Analysis and Machine Intelligence 14 (1992)] and its most salient feature is its ability to simultaneously measuring wavefront maps and distances to objects [Wavefront and distance measurements using the CAFADIS camera, in Astronomical telescopes, Marseille (2008)]. This makes of CAFADIS an interesting alternative for LGS-based AO systems as it is capable of measuring from an LGS-beacon the atmospheric turbulence wavefront and simultaneously the distance to the LGS beacon thus removing the need of a NGS defocus sensor to probe changes in distance to the LGS beacon due to drifts of the mesospheric Na layer. In principle, the concept can also be employed to recover 3D profiles of the Na Layer allowing for optimizations of the measurement of the distance to the LGS-beacon. Currently we are investigating the possibility of extending the plenoptic WFS into a tomographic wavefront sensor. Simulations will be shown of a plenoptic WFS when operated within an LGS-based AO system for the recovery of wavefront maps at different heights. The preliminary results presented here show the tomographic ability of CAFADIS.

James Webb Space telescope optical simulation testbed: experimental results with linear control alignment

NASA Astrophysics Data System (ADS)

Egron, Sylvain; Lajoie, Charles-Philippe; Michau, Vincent; Bonnefois, Aurélie; Escolle, Clément; Leboulleux, Lucie; N'Diaye, Mamadou; Pueyo, Laurent; Choquet, Elodie; Perrin, Marshall D.; Ygouf, Marie; Fusco, Thierry; Ferrari, Marc; Hugot, Emmanuel; Soummer, Rémi

2017-09-01

The current generation of terrestrial telescopes has large enough primary mirror diameters that active optical control based on wavefront sensing is necessary. Similarly, in space, while the Hubble Space Telescope (HST) has a mostly passive optical design, apart from focus control, its successor the James Webb Space Telescope (JWST) has active control of many degrees of freedom in its primary and secondary mirrors.

Lenses that provide the transformation between two given wavefronts

NASA Astrophysics Data System (ADS)

Criado, C.; Alamo, N.

2016-12-01

We give an original method to design four types of lenses solving the following problems: focusing a given wavefront in a given point, and performing the transformation between two arbitrary incoming and outgoing wavefronts. The method to design the lenses profiles is based on the optical properties of the envelopes of certain families of Cartesian ovals of revolution.

Beam characterization by wavefront sensor

DOEpatents

Neal, Daniel R.; Alford, W. J.; Gruetzner, James K.

1999-01-01

An apparatus and method for characterizing an energy beam (such as a laser) with a two-dimensional wavefront sensor, such as a Shack-Hartmann lenslet array. The sensor measures wavefront slope and irradiance of the beam at a single point on the beam and calculates a space-beamwidth product. A detector array such as a charge coupled device camera is preferably employed.

Wavefront Reconstruction and Mirror Surface Optimizationfor Adaptive Optics

DTIC Science & Technology

2014-06-01

TERMS Wavefront reconstruction, Adaptive optics , Wavelets, Atmospheric turbulence , Branch points, Mirror surface optimization, Space telescope, Segmented...contribution adapts the proposed algorithm to work when branch points are present from significant atmospheric turbulence . An analysis of vector spaces...estimate the distortion of the collected light caused by the atmosphere and corrected by adaptive optics . A generalized orthogonal wavelet wavefront

Stability of corneal topography and wavefront aberrations in young Singaporeans.

PubMed

Zhu, Mingxia; Collins, Michael J; Yeo, Anna C H

2013-09-01

The aim was to investigate the differences between and variations across time in corneal topography and ocular wavefront aberrations in young Singaporean myopes and emmetropes. We used a videokeratoscope and wavefront sensor to measure the ocular surface topography and wavefront aberrations of the total-eye optics in the morning, midday and late afternoon on two separate days. Topographic data were used to derive the corneal surface wavefront aberrations. Both the corneal and total wavefronts were analysed up to the fourth radial order of the Zernike polynomial expansion and were centred on the entrance pupil (5.0 mm). The participants included 12 young progressing myopes, 13 young stable myopes and 15 young age-matched emmetropes. For all subjects considered together, there were significant changes in some of the aberrations across the day, such as spherical aberration ( Z(4 0)) and vertical coma ( Z (3 - 1)) (repeated measures analysis of variance, p < 0.05). The magnitude of positive spherical aberration ( Z(4 0)) was significantly lower in the progressing myopic group than in the stable myopic (p = 0.04) and emmetropic (p = 0.02) groups. There were also significant interactions between refractive group and time of day for with and against-the-rule astigmatism ( Z(2 2)). Significantly lower fourth-order root mean square of ocular wavefront aberrations were found in the progressing myopic group compared with the stable myopes and emmetropes (p < 0.01). These differences and variations in the corneal and total aberrations may have significance for our understanding of refractive error development and for clinical applications requiring accurate wavefront measurements. © 2013 The Authors. Clinical and Experimental Optometry © 2013 Optometrists Association Australia.

Spatially resolved wavefront aberrations of ophthalmic progressive-power lenses in normal viewing conditions.

PubMed

Villegas, Eloy A; Artal, Pablo

2003-02-01

To measure the wavefront aberration at different locations in progressive-power lenses (PPL's) isolated and in situ (PPL's plus eye). A Hartmann-Shack wavefront sensor was used to measure progressive-power lenses and human eyes either independently or in combination. In each selected zone, the lens was placed and tilted accordingly to simulate natural viewing conditions. We measured 21 relevant locations across an isolated PPL (plano lens of power addition of 2 D). In six of the locations, the wavefront aberration of the eye plus PPL were obtained in two ways: (1) by direct measurement of the system and (2) by adding the individual wavefront aberrations of the eye and the lens for each appropriate zone. In every case, we obtained the wavefront aberration as Zernike polynomials expansions, the root mean square error, the point-spread function, and the Strehl ratio. Along the corridor of the PPL, third-order coma and trefoil, and astigmatism were the dominant aberrations. In areas of the PPL outside the corridor, astigmatism increased, whereas other aberrations remained similar to the lens center. Small differences were found between the direct and calculated methods used to obtain the wavefront aberration of the eye with the lens, and the possible sources of errors were discussed. In some lenses zones, the aberrations of the lens may be compensated by the particular aberrations of the eye, yielding improved optical performance over that present in the lens alone. We designed and built a wavefront sensor to perform spatially resolved aberration measurements in ophthalmic lenses, in particular in PPL's, either isolated or in combination with the eye. The aberrations appearing in the PPL were compared with those in normal aged eyes.

Fast Holographic Wavefront Sensor

NASA Astrophysics Data System (ADS)

Andersen, G.; Ghebremichael, F.; Gurley, K.

There are several different types of wavefront sensors that can be used to measure the phase of an input beam. While they have widely varying modes of operation, they all require some computational overhead in order to deconstruct the phase from an optical measurement which greatly reduces the sensing speed. Furthermore, zonal detection methods, such as the Shack-Hartmann wavefront sensor (SHWFS) are not well suited to temporal changes in pupil obscuration such as can occur with scintillation. Here we present a modal detector that incorporates a multiplexed hologram to give a full description of wavefront error without the need for any calculations. The holographic wavefront sensor (HWFS) uses a hologram that is "pre-programmed" with all desired Zernike aberration components. An input beam of arbitrary phase will diffract into pairs of focused beams. Each pair represents a different aberration, and the amplitude is obtained by measuring the relative brightness of the pair of foci. This can be easily achieved by using conventional position sensing devices. In this manner, the amplitudes of each aberration components are directly sensed without the need for any calculations. As such, a complete characterization of the wavefront can be made at speeds of up to 100 kHz in a compact device and without the need for a computer or sophisticated electronics. In this talk we will detail the operation of the holographic wavefront sensor and present results of a prototype sensor as well as a modified design suitable for a closed-loop adaptive optics system. This new wavefront sensor will not only permit faster correction, but permit adaptive optics systems to work in extremely turbulent environments such as those encountered in fast-tracking systems and the Airborne Laser project.

Identification of the focal plane wavefront control system using E-M algorithm

NASA Astrophysics Data System (ADS)

Sun, He; Kasdin, N. Jeremy; Vanderbei, Robert

2017-09-01

In a typical focal plane wavefront control (FPWC) system, such as the adaptive optics system of NASA's WFIRST mission, the efficient controllers and estimators in use are usually model-based. As a result, the modeling accuracy of the system influences the ultimate performance of the control and estimation. Currently, a linear state space model is used and calculated based on lab measurements using Fourier optics. Although the physical model is clearly defined, it is usually biased due to incorrect distance measurements, imperfect diagnoses of the optical aberrations, and our lack of knowledge of the deformable mirrors (actuator gains and influence functions). In this paper, we present a new approach for measuring/estimating the linear state space model of a FPWC system using the expectation-maximization (E-M) algorithm. Simulation and lab results in the Princeton's High Contrast Imaging Lab (HCIL) show that the E-M algorithm can well handle both the amplitude and phase errors and accurately recover the system. Using the recovered state space model, the controller creates dark holes with faster speed. The final accuracy of the model depends on the amount of data used for learning.

Lenslet Array to Further Suppress Star Light for Direct Exoplanet Detection

NASA Technical Reports Server (NTRS)

Gong, Qian; McElwain, Michael; Shiri, Ron

2016-01-01

Direct imaging plays a key role in the detection and characterization of exoplanets orbiting within its host star's habitable zone. Many innovative ideas for starlight suppression and wavefront control have been proposed and developed over the past decade. However, several technological challenges still lie ahead to achieve the required contrast, including controlling the observatory pointing performance, fabricating occulting masks with tight optical tolerances, developing wavefront control algorithms, controlling stray light, advancing single photon detecting detectors, and integrated system-level issues. This paper explores how a lenslet array and pinhole mask may be implemented to further suppress uncorrected starlight that leaks through the occulting mask. An external occulter, or star shade, is simulated to demonstrate this concept, although this approach can be implemented for internal coronagraphs as well. We describe how to use simple relay optics to control the scene near the inner working angle and the level of the suppression expected. Furthermore, if the lenslet array is the input to an integral field spectrograph, as planned for the WFIRST mission, the spectral content of the exoplanet atmospheres can be obtained to determine if the observed planet is habitable and ultimately, if it is inhabited.

Gradient descent algorithm applied to wavefront retrieval from through-focus images by an extreme ultraviolet microscope with partially coherent source

DOE PAGES

Yamazoe, Kenji; Mochi, Iacopo; Goldberg, Kenneth A.

2014-12-01

The wavefront retrieval by gradient descent algorithm that is typically applied to coherent or incoherent imaging is extended to retrieve a wavefront from a series of through-focus images by partially coherent illumination. For accurate retrieval, we modeled partial coherence as well as object transmittance into the gradient descent algorithm. However, this modeling increases the computation time due to the complexity of partially coherent imaging simulation that is repeatedly used in the optimization loop. To accelerate the computation, we incorporate not only the Fourier transform but also an eigenfunction decomposition of the image. As a demonstration, the extended algorithm is appliedmore » to retrieve a field-dependent wavefront of a microscope operated at extreme ultraviolet wavelength (13.4 nm). The retrieved wavefront qualitatively matches the expected characteristics of the lens design.« less

Precise calibration of pupil images in pyramid wavefront sensor.

PubMed

Liu, Yong; Mu, Quanquan; Cao, Zhaoliang; Hu, Lifa; Yang, Chengliang; Xuan, Li

2017-04-20

The pyramid wavefront sensor (PWFS) is a novel wavefront sensor with several inspiring advantages compared with Shack-Hartmann wavefront sensors. The PWFS uses four pupil images to calculate the local tilt of the incoming wavefront. Pupil images are conjugated with a telescope pupil so that each pixel in the pupil image is diffraction-limited by the telescope pupil diameter, thus the sensing error of the PWFS is much lower than that of the Shack-Hartmann sensor and is related to the extraction and alignment accuracy of pupil images. However, precise extraction of these images is difficult to conduct in practice. Aiming at improving the sensing accuracy, we analyzed the physical model of calibration of a PWFS and put forward an extraction algorithm. The process was verified via a closed-loop correction experiment. The results showed that the sensing accuracy of the PWFS increased after applying the calibration and extraction method.

Feasibility study of a layer-oriented wavefront sensor for solar telescopes.

PubMed

Marino, Jose; Wöger, Friedrich

2014-02-01

Solar multiconjugate adaptive optics systems rely on several wavefront sensors, which measure the incoming turbulent phase along several field directions to produce a tomographic reconstruction of the turbulent phase. In this paper, we explore an alternative wavefront sensing approach that attempts to directly measure the turbulent phase present at a particular height in the atmosphere: a layer-oriented cross-correlating Shack-Hartmann wavefront sensor (SHWFS). In an experiment at the Dunn Solar Telescope, we built a prototype layer-oriented cross-correlating SHWFS system conjugated to two separate atmospheric heights. We present the data obtained in the observations and complement these with ray-tracing computations to achieve a better understanding of the instrument's performance and limitations. The results obtained in this study strongly indicate that a layer-oriented cross-correlating SHWFS is not a practical design to measure the wavefront at a high layer in the atmosphere.

Holographic wavefront sensor, based on diffuse Fourier holography

NASA Astrophysics Data System (ADS)

Gorelaya, Alina; Orlov, Vyacheslav; Venediktov, Vladimir

2017-09-01

Many areas of optical science and technology require fast and accurate measurement of the radiation wavefront shape. Today there are known a lot of wavefront sensor (WFS) techniques, and their number is growing up. The last years have brought a growing interest in several schematics of WFS, employing the holography principles and holographic optical elements (HOE). Some of these devices are just the improved versions of the standard and most popular Shack-Hartman WFS, while other are based on the intrinsic features of HOE. A holographic mode wavefront sensor is proposed, which makes it possible to measure up to several tens of wavefront modes. The increase in the number of measured modes is implemented using the conversion of a light wave entering the sensor into a wide diffuse light beam, which allows one to record a large number of holograms, each intended for measuring one of the modes.

Closed loop adaptive optics for microscopy without a wavefront sensor.

PubMed

Kner, Peter; Winoto, Lukman; Agard, David A; Sedat, John W

2010-02-24

A three-dimensional wide-field image of a small fluorescent bead contains more than enough information to accurately calculate the wavefront in the microscope objective back pupil plane using the phase retrieval technique. The phase-retrieved wavefront can then be used to set a deformable mirror to correct the point-spread function (PSF) of the microscope without the use of a wavefront sensor. This technique will be useful for aligning the deformable mirror in a widefield microscope with adaptive optics and could potentially be used to correct aberrations in samples where small fluorescent beads or other point sources are used as reference beacons. Another advantage is the high resolution of the retrieved wavefont as compared with current Shack-Hartmann wavefront sensors. Here we demonstrate effective correction of the PSF in 3 iterations. Starting from a severely aberrated system, we achieve a Strehl ratio of 0.78 and a greater than 10-fold increase in maximum intensity.

Gradient descent algorithm applied to wavefront retrieval from through-focus images by an extreme ultraviolet microscope with partially coherent source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamazoe, Kenji; Mochi, Iacopo; Goldberg, Kenneth A.

The wavefront retrieval by gradient descent algorithm that is typically applied to coherent or incoherent imaging is extended to retrieve a wavefront from a series of through-focus images by partially coherent illumination. For accurate retrieval, we modeled partial coherence as well as object transmittance into the gradient descent algorithm. However, this modeling increases the computation time due to the complexity of partially coherent imaging simulation that is repeatedly used in the optimization loop. To accelerate the computation, we incorporate not only the Fourier transform but also an eigenfunction decomposition of the image. As a demonstration, the extended algorithm is appliedmore » to retrieve a field-dependent wavefront of a microscope operated at extreme ultraviolet wavelength (13.4 nm). The retrieved wavefront qualitatively matches the expected characteristics of the lens design.« less

Beam quality management by periodic reproduction of wavefront aberrations in end-pumped Nd:YVO₄ laser amplifiers.

PubMed

Liu, Bin; Liu, Chong; Shen, Lifeng; Wang, Chunhua; Ye, Zhibin; Liu, Dong; Xiang, Zhen

2016-04-18

A method for beam quality management is presented in a master oscillator power amplifier (MOPA) using Nd:YVO₄ as the gain medium by extra-cavity periodic reproduction of wavefront aberrations. The wavefront aberration evolution of the intra-cavity beams is investigated for both symmetrical and asymmetrical resonators. The wavefront aberration reproduction process is successfully realized outside the cavity in four-stage amplifiers. In the MOPA with a symmetrical oscillator, the laser power increases linearly and the beam quality hardly changes. In the MOPA with an asymmetrical oscillator, the beam quality is deteriorated after the odd-stage amplifier and is improved after the even-stage amplifier. The wavefront aberration reproduction during the extra-cavity beam propagation in the amplifiers is equivalent to that during the intra-cavity propagation. This solution helps to achieve the effective beam quality management in laser amplifier chains.

High speed digital holography for density and fluctuation measurements (invited).

PubMed

Thomas, C E; Baylor, L R; Combs, S K; Meitner, S J; Rasmussen, D A; Granstedt, E M; Majeski, R P; Kaita, R

2010-10-01

The state of the art in electro-optics has advanced to the point where digital holographic acquisition of wavefronts is now possible. Holographic wavefront acquisition provides the phase of the wavefront at every measurement point. This can be done with accuracy on the order of a thousandth of a wavelength, given that there is sufficient care in the design of the system. At wave frequencies which are much greater than the plasma frequency, the plasma index of refraction is linearly proportional to the electron density and wavelength, and the measurement of the phase of a wavefront passing through the plasma gives the chord-integrated density directly for all points measured on the wavefront. High-speed infrared cameras (up to ∼40,000 fps at ∼64×4 pixels) with resolutions up to 640×512 pixels suitable for use with a CO(2) laser are readily available, if expensive.

Wavefront division digital holography

NASA Astrophysics Data System (ADS)

Zhang, Wenhui; Cao, Liangcai; Li, Rujia; Zhang, Hua; Zhang, Hao; Jiang, Qiang; Jin, Guofan

2018-05-01

Digital holography (DH), mostly Mach-Zehnder configuration based, belongs to non-common path amplitude splitting interference imaging whose stability and fringe contrast are environmental sensitive. This paper presents a wavefront division DH configuration with both high stability and high-contrast fringes benefitting from quasi common path wavefront-splitting interference. In our proposal, two spherical waves with similar curvature coming from the same wavefront are used, which makes full use of the physical sampling capacity of the detectors. The interference fringe spacing can be adjusted flexibly for both in-line and off-axis mode due to the independent modulation to these two waves. Only a few optical elements, including the mirror-beam splitter interference component, are used without strict alignments, which makes it robust and easy-to-implement. The proposed wavefront division DH promotes interference imaging physics into the practical and miniaturized a step forward. The feasibility of this method is proved by the imaging of a resolution target and a water flea.

High-resolution wavefront reconstruction using the frozen flow hypothesis

NASA Astrophysics Data System (ADS)

Liu, Xuewen; Liang, Yonghui; Liu, Jin; Xu, Jieping

2017-10-01

This paper describes an approach to reconstructing wavefronts on finer grid using the frozen flow hypothesis (FFH), which exploits spatial and temporal correlations between consecutive wavefront sensor (WFS) frames. Under the assumption of FFH, slope data from WFS can be connected to a finer, composite slope grid using translation and down sampling, and elements in transformation matrices are determined by wind information. Frames of slopes are then combined and slopes on finer grid are reconstructed by solving a sparse, large-scale, ill-posed least squares problem. By using reconstructed finer slope data and adopting Fried geometry of WFS, high-resolution wavefronts are then reconstructed. The results show that this method is robust even with detector noise and wind information inaccuracy, and under bad seeing conditions, high-frequency information in wavefronts can be recovered more accurately compared with when correlations in WFS frames are ignored.

System for the design, manufacture, and testing of custom lenses with known amounts of high-order aberrations.

PubMed

Chernyak, Dimitri A; Campbell, Charles E

2003-11-01

Now that excimer laser systems can be programmed to correct complex aberrations of the eye on the basis of wave-front measurements, a method is needed to test the accuracy of the system from measurement through treatment. A closed-loop test method was developed to ensure that treatment plans generated by a wavefront measuring system were accurately transferred to and executed by the excimer laser. A surface was analytically defined, and a Shack-Hartmann-based wave-front system was used to formulate a treatment plan, which was downloaded to an excimer laser system. A plastic lens was ablated by the laser and then returned to the wave-front device, where it was measured and compared with the analytically defined wave-front surface. The two surfaces agreed up to 6th-order Zernike terms, validating the accuracy of the system.

Advanced Imaging Optics Utilizing Wavefront Coding.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scrymgeour, David; Boye, Robert; Adelsberger, Kathleen

2015-06-01

Image processing offers a potential to simplify an optical system by shifting some of the imaging burden from lenses to the more cost effective electronics. Wavefront coding using a cubic phase plate combined with image processing can extend the system's depth of focus, reducing many of the focus-related aberrations as well as material related chromatic aberrations. However, the optimal design process and physical limitations of wavefront coding systems with respect to first-order optical parameters and noise are not well documented. We examined image quality of simulated and experimental wavefront coded images before and after reconstruction in the presence of noise.more » Challenges in the implementation of cubic phase in an optical system are discussed. In particular, we found that limitations must be placed on system noise, aperture, field of view and bandwidth to develop a robust wavefront coded system.« less

BER Analysis of Coherent Free-Space Optical Communication Systems with a Focal-Plane-Based Wavefront Sensor

NASA Astrophysics Data System (ADS)

Cao, Jingtai; Zhao, Xiaohui; Liu, Wei; Gu, Haijun

2018-03-01

A wavefront sensor is one of most important units for an adaptive optics system. Based on our previous works, in this paper, we discuss the bit-error-rate (BER) performance of coherent free space optical communication systems with a focal-plane-based wavefront sensor. Firstly, the theory of a focal-plane-based wavefront sensor is given. Then the relationship between the BER and the mixing efficiency with a homodyne receiver is discussed on the basis of binary-phase-shift-keying (BPSK) modulation. Finally, the numerical simulation results are shown that the BER will be decreased obviously after aberrations correction with the focal-plane-based wavefront sensor. In addition, the BER will decrease along with increasing number of photons received within a single bit. These analysis results will provide a reference for the design of the coherent Free space optical communication (FSOC) system.

Two-dimensional wavefront reconstruction based on double-shearing and least squares fitting

NASA Astrophysics Data System (ADS)

Liang, Peiying; Ding, Jianping; Zhu, Yangqing; Dong, Qian; Huang, Yuhua; Zhu, Zhen

2017-06-01

The two-dimensional wavefront reconstruction method based on double-shearing and least squares fitting is proposed in this paper. Four one-dimensional phase estimates of the measured wavefront, which correspond to the two shears and the two orthogonal directions, could be calculated from the differential phase, which solves the problem of the missing spectrum, and then by using the least squares method the two-dimensional wavefront reconstruction could be done. The numerical simulations of the proposed algorithm are carried out to verify the feasibility of this method. The influence of noise generated from different shear amount and different intensity on the accuracy of the reconstruction is studied and compared with the results from the algorithm based on single-shearing and least squares fitting. Finally, a two-grating lateral shearing interference experiment is carried out to verify the wavefront reconstruction algorithm based on doubleshearing and least squares fitting.

Wavefront attributes in anisotropic media

NASA Astrophysics Data System (ADS)

Vanelle, C.; Abakumov, I.; Gajewski, D.

2018-07-01

Surface-measured wavefront attributes are the key ingredient to multiparameter methods, which are nowadays standard tools in seismic data processing. However, most operators are restricted to application to isotropic media. Whereas application of an isotropic operator will still lead to satisfactory stack results, further processing steps that interpret isotropic stacking parameters in terms of wavefront attributes will lead to erroneous results if anisotropy is present but not accounted for. In this paper, we derive relationships between the stacking parameters and anisotropic wavefront attributes that allow us to apply the common reflection surface type operator to 3-D media with arbitrary anisotropy for the zero-offset and finite-offset configurations including converted waves. The operator itself is expressed in terms of wavefront attributes that are measured in the acquisition surface, that is, no model assumptions are made. Numerical results confirm that the accuracy of the new anisotropic operator is of the same magnitude as that of its isotropic counterpart.