Measurement Of Aberrations Research Articles

Customized models of ocular aberrations across the visual field during accommodation.

We aimed to create individual eye models that accurately reproduce the empirical measurements of wave-front aberrations across the visual field at different accommodative states, thus providing a mechanistic explanation for the changes in the eye's aberration structure due to accommodation. Structural parameters of a generic eye model were optimized using optical design software to account for published measurements of wave-front aberrations measured for 19 individuals at 37 test locations over the central 30°-diameter visual field at eight levels of accommodative demand. Biometric data for individual eyes were used as starting values and normative data were used to constrain optimizations to anatomically reasonable values. Customizations of the accommodating eye model accurately accounted for ocular aberrations over the central 30° of visual field with an averaged root mean square fitting error typically below 0.2 μm at any given field location. Optimized structural parameters of the eye models were anatomically reasonable and changed in the expected way when accommodating. Accuracy for representing spherical aberration was significantly improved by relaxing anatomical constraints on the anterior surface of the lens to compensate for not including gradient-index media. Use of the model to compute pan-retinal image quality revealed large penalties of accommodative lag for activating photoreceptor responses to the retinal image.

Improving Stockline Detection of Radar Sensor Array Systems in Blast Furnaces Using a Novel Encoder-Decoder Architecture.

The stockline, which describes the measured depth of the blast furnace (BF) burden surface with time, is significant to the operator executing an optimized charging operation. For the harsh BF environment, noise interferences and aberrant measurements are the main challenges of stockline detection. In this paper, a novel encoder–decoder architecture that consists of a convolution neural network (CNN) and a long short-term memory (LSTM) network is proposed, which suppresses the noise interferences, classifies the distorted signals, and regresses the stockline in a learning way. By leveraging the LSTM, we are able to model the longer historical measurements for robust stockline tracking. Compared to traditional hand-crafted denoising processing, the time and efforts could be greatly saved. Experiments are conducted on an actual eight-radar array system in a blast furnace, and the effectiveness of the proposed method is demonstrated on the real recorded data.

Phase diversity algorithm with high noise robust based on deep denoising convolutional neural network.

The wave-front phase expanded on the Zernike polynomials is estimated from a pair of images by the use of a maximum-likelihood approach, the in-focus image and the defocus image, which contaminated by noise, will greatly reduce the solution accuracy of the phase diversity (PD) algorithm. In the study, we introduce the deep denoising convolutional neural networks (DnCNNs) into the image preprocessing of PD to denoise the in-focus image and defocus the image containing gaussian white noise to improve the robustness of PD to noise. The simulation results show that the composite PD algorithm with DnCNNs is better than the traditional PD algorithm in both RMSE of phase estimation and SSIM, and the mean of the RMSE of the phase estimation of the improved PD algorithm is reduced by 78.48%, 82.35%, 71.09% and 73.67% compared with the mean of the RMSE of the phase estimation of the traditional PD algorithm. The well-trained DnCNNs runs fast, which does not increase the running time of traditional PD algorithms, and the compound approach may be widely used in various domains, such as the measurements of intrinsic aberrations in optical systems and compensations for atmospheric turbulence.

Noninvasive imaging of the tree shrew eye: Wavefront analysis and retinal imaging with correlative histology

Tree shrews are small mammals with excellent vision and are closely related to primates. They have been used extensively as a model for studying refractive development, myopia, and central visual processing and are becoming an important model for vision research. Their cone dominant retina (∼95% cones) provides a potential avenue to create new damage/disease models of human macular pathology and to monitor progression or treatment response. To continue the development of the tree shrew as an animal model, we provide here the first measurements of higher order aberrations along with adaptive optics scanning light ophthalmoscopy (AOSLO) images of the photoreceptor mosaic in the tree shrew retina. To compare intra-animal in vivo and ex vivo cone density measurements, the AOSLO images were matched to whole-mount immunofluorescence microscopy. Analysis of the tree shrew wavefront indicated that the optics are well-matched to the sampling of the cone mosaic and is consistent with the suggestion that juvenile tree shrews are nearly emmetropic (slightly hyperopic). Compared with in vivo measurements, consistently higher cone density was measured ex vivo, likely due to tissue shrinkage during histological processing. Tree shrews also possess massive mitochondria (“megamitochondria”) in their cone inner segments, providing a natural model to assess how mitochondrial size affects in vivo retinal imagery. Intra-animal in vivo and ex vivo axial distance measurements were made in the outer retina with optical coherence tomography (OCT) and transmission electron microscopy (TEM), respectively, to determine the origin of sub-cellular cone reflectivity seen on OCT. These results demonstrate that these megamitochondria create an additional hyper-reflective outer retinal reflective band in OCT images. The ability to use noninvasive retinal imaging in tree shrews supports development of this species as a model of cone disorders.

Quantitative aberration measurement with extended ptychographic iterative engine

A computational method is proposed to measure the aberration of a lens using an extended ptychographic iterative engine. By reconstructing the entering wavefront φin and exiting wavefront φex of the lens under detection from two sets of diffraction patterns iteratively, the lens aberration can be easily extracted by subtracting the phase of φin and theoretical lens phase from the phase of φex. Since it needs no extra reference beam and high quality optics, this suggested method has advantages of simplicity in structure, high accuracy, and low requirement on working environment, and it is free of the aberration of other optical elements in the experimental system, indicating it can find lots of applications in lens evaluation.

Visual Function at the Atrophic Border in Choroideremia Assessed with Adaptive Optics Microperimetry

Recent advances in retinal imaging allow visualization of structural abnormalities in retinal disease at the cellular level. This study used adaptive optics (AO) microperimetry to assess visual sensitivity with high spatial precision and to examine how function varies across 2 phenotypic features observed in choroideremia: atrophic lesion borders and outer retinal tubulations (ORTs). Cross-sectional study. Twelve choroideremia patients. A custom AO scanning light ophthalmoscope (AOSLO) equipped with both confocal and nonconfocalsplit-detection imaging methods was used to image the photoreceptor inner and outer segment mosaics. For AO microperimetry, circular 550-nm stimuli were presented through the AOSLO system; stimuli were either 9.6 or 38.3 arcmin2 (approximately 60 or 15 times smaller than a Goldman III stimulus). Test locations were identified in structural images and stimuli were targeted to these locations using real-time retinal tracking combined with measurements of transverse chromatic aberration. Psychophysical detection thresholds were measured at the atrophic border in 12 patients. Additionally, visual sensitivity was probed along ORTs in 4patients. Visual sensitivity thresholds measured with AO microperimetry at retinal locations corresponding to structural phenotypes observed on AOSLO retinal images. In choroideremia, sharp borders between intact central islands of the photoreceptor mosaic and complete atrophy of the outer retina and retinal pigment epithelium were observed in both split-detection and confocal structural images. Adaptive optics microperimetry at locations spanning these borders showed a commensurately sharp decrease in function, with readily measurable visual sensitivity on one side and dense scotoma on the other. These functional transitions often occurred over a distance smaller than the diameter of the Goldman III stimulus. Thresholds measured along ORTs showed dense scotoma over the tubule in all 4 participants, despite the visibility of remnant cone inner segments on the AO images. Choroideremia patients exhibited sharp functional transitions that collocated with structural transitions from intact to severely degenerated retina. We found no evidence of visual sensitivity over ORTs. Measuring cone function with high resolution offered insight into disease mechanisms and may enable precise assessment of whether experimental therapies, such as gene therapy, provide a functional benefit.

Full-field Fourier ptychography (FFP): Spatially varying pupil modeling and its application for rapid field-dependent aberration metrology

Digital aberration measurement and removal play a prominent role in computational imaging platforms aimed at achieving simple and compact optical arrangements. A recent important class of such platforms is Fourier ptychography (FP), which is geared toward efficiently creating gigapixel images with high resolution and large field of view (FOV). In current FP implementations, pupil aberration is often recovered at each small segment of the entire FOV. This reconstruction strategy fails to consider the field-dependent nature of the optical pupil. Given the power series expansion of the wavefront aberration, the spatially varying pupil can be fully characterized by tens of coefficients over the entire FOV. With this observation, we report a Full-field Fourier Ptychography (FFP) scheme for rapid and robust aberration metrology. The meaning of “full-field” in FFP is referred to the recovery of the “full-field” coefficients that govern the field-dependent pupil over the entire FOV. The optimization degrees of freedom are at least two orders of magnitude lower than the previous implementations. We show that the image acquisition process of FFP can be completed in ∼1 s and the spatially varying aberration of the entire FOV can be recovered in ∼35 s using a central processing unit. The reported approach may facilitate the further development of FP. Since no moving part or calibration target is needed in this approach, it may find important applications in aberration metrology. The derivation of the full-field coefficients and its extension for Zernike modes also provide a general tool for analyzing spatially varying aberrations in computational imaging systems.

Method for designing phase-retrieval algorithms for Ronchi phase-shifting lateral-shearing interferometry.

We propose a general method of designing phase-analysis algorithms for Ronchi phase-shifting lateral-shearing interferometry. Based on the expression and method, three new phase-shifting algorithms are designed to eliminate negative error effects of interference from unwanted diffraction orders, which limits the accuracy of wavefront aberration measurement. The proposed eight-, 10-, and 13-frame algorithms can eliminate the effects of the first ±5, ±9, and ±15 multi-diffraction orders, respectively. Simulation works and experimental results verify the general expression and corresponding designed method.

Corneal higher-order aberrations measurements: Comparison between Scheimpflug and dual Scheimpflug–Placido technology in keratoconic eyes

To compare the difference and agreement of corneal higher-order aberrations (HOAs) in keratoconic eyes using Scheimpflug and dual Scheimpflug-Placido imaging systems. Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, California, USA. Retrospective between-devices reliability and agreement study. Patients diagnosed with keratoconus were evaluated sequentially by Scheimpflug and dual Scheimpflug-Placido devices. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated. Fifty eyes from 50 patients (31 men, 19 women) were evaluated. Trefoil at 30 degrees, spherical aberration, and total RMS were significantly different between groups (P<.05), whereas trefoil at 0 degrees and total coma values were not statistically different. There was a weak positive correlation between devices for trefoil at 0 degrees (r=0.228), and a moderate positive correlation for trefoil at 30 degrees (r=0.473), horizontal coma (r=0.430), and for total corneal RMS (r=0.637). Vertical coma (r=0.816) and spherical aberration (r=0.874) showed a strong positive correlation. The 95% limits of agreement (LoA) for absolute values were 1.963μm for trefoil at 30 degrees, 2.449μm for trefoil at 0 degrees, 3.530μm for horizontal coma, 2.145μm for vertical coma, 1.242μm for spherical aberration, and 10.527μm for RMS. Significant differences were found between measurements of corneal HOAs generated by Scheimpflug and dual Scheimpflug-Placido devices in patients with keratoconus, with generally limited correlations and wide LoA. HOAs measurements from these devices should not be considered equivalent.

Identification of the dynamics of time-varying phase aberrations from time histories of the point-spread function.

To optimally compensate for time-varying phase aberrations with adaptive optics, a model of the dynamics of the aberrations is required to predict the phase aberration at the next time step. We model the time-varying behavior of a phase aberration, expressed in Zernike modes, by assuming that the temporal dynamics of the Zernike coefficients can be described by a vector-valued autoregressive (VAR) model. We propose an iterative method based on a convex heuristic for a rank-constrained optimization problem, to jointly estimate the parameters of the VAR model and the Zernike coefficients from a time series of measurements of the point-spread function (PSF) of the optical system. By assuming the phase aberration is small, the relation between aberration and PSF measurements can be approximated by a quadratic function. As such, our method is a blind identification method for linear dynamics in a stochastic Wiener system with a quadratic nonlinearity at the output and a phase retrieval method that uses a time-evolution-model constraint and a single image at every time step.

Ptychography as a wavefront sensor for high-numerical aperture extreme ultraviolet lithography: analysis and limitations

Wavefront aberration measurements are required to test an extreme ultraviolet (EUV) imaging system. For a high-NA EUV imaging system, where conventional wavefront-sensing techniques show limitations, ptychography can be used for this purpose. However, at the wavelength region of EUV (i.e., 13.5 nm), the position accuracy of the scanning mask that is defined for ptychography is stringent. Therefore, we propose ptychography combined with mask position correction. The simulated intensity patterns, the ones we use, resemble expected EUV experimental data. Finally, we show the results in the presence of Poisson noise and the tolerance of the position correction method for error in mask positions.

Large dynamic range autorefraction with a low-cost diffuser wavefront sensor.

Wavefront sensing with a thin diffuser has emerged as a potential low-cost alternative to a lenslet array for aberrometry. Here we show that displacement of caustic patterns can be tracked for estimating wavefront gradient in a diffuser wavefront sensor (DWFS), enabling large dynamic-range wavefront measurements with sufficient accuracy for eyeglass prescription measurements. We compare the dynamic range, repeatability, precision, and number of resolvable prescriptions of a DWFS to a Shack-Hartmann wavefront sensor (SHWFS) for autorefraction measurement. We induce spherical and cylindrical errors in a model eye and use a multi-level Demon's non-rigid registration algorithm to estimate caustic displacements relative to an emmetropic model eye. When compared to spherical error measurements with the SHWFS using a laser diode with a laser speckle reducer, the DWFS demonstrates a ∼5-fold improvement in dynamic range (-4.0 to +4.5 D vs. -22.0 to +19.5 D) with less than half the reduction in resolution (0.072 vs. 0.116 D), enabling a ∼3-fold increase in the number of resolvable prescriptions (118 vs. 358). In addition to being lower-cost, the unique, non-periodic nature of the caustic pattern formed by a diffuser enables a larger dynamic range of aberration measurements compared to a lenslet array.

Measuring Ocular Aberrations Sequentially Using a Digital Micromirror Device.

The Hartmann–Shack wavefront sensor is widely used to measure aberrations in both astronomy and ophthalmology. Yet, the dynamic range of the sensor is limited by cross-talk between adjacent lenslets. In this study, we explore ocular aberration measurements with a recently-proposed variant of the sensor that makes use of a digital micromirror device for sequential aperture scanning of the pupil, thereby avoiding the use of a lenslet array. We report on results with the sensor using two different detectors, a lateral position sensor and a charge-coupled device (CCD) scientific camera, and explore the pros and cons of both. Wavefront measurements of a highly aberrated artificial eye and of five real eyes, including a highly myopic subject, are demonstrated, and the role of pupil sampling density, CCD pixel binning, and scanning speed are explored. We find that the lateral position sensor is mostly suited for high-power applications, whereas the CCD camera with pixel binning performs consistently well both with the artificial eye and for real-eye measurements, and can outperform a commonly-used wavefront sensor with highly aberrated wavefronts.

Measuring chromatic aberration in LEEM/PEEM

Measurement of chromatic aberration in a Low Energy Electron Microscope (LEEM) or Photo Electron Emission Microscope (PEEM) is necessary for quantitative image interpretation, and for accurate correction of chromatic aberration in an aberration-corrected instrument. While methods have been developed for measuring the spherical aberration coefficient, C3, measuring the chromatic aberration coefficient, Cc, remains a more difficult task. Here a novel method is introduced to simplify such measurements. The viability and accuracy is demonstrated using detailed electron-optical ray-tracing calculations. Experimental results show that the method is easily reduced to practice.

Higher-order aberration measurements: Comparison between Scheimpflug and dual Scheimpflug–Placido technology in normal eyes

To compare higher order aberrations (HOAs) in normal eyes between a Scheimpflug imaging system (Pentacam HR) and dual Scheimpflug-Placido imaging system (Galilei G4). Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, USA. Retrospective case series. Eyes screened for refractive surgery were evaluated sequentially using a Scheimpflug device and a dual Scheimpflug-Placido device. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated. One hundred five eyes of 105 patients (44 men, 61 women) were evaluated. Total RMS, coma, and trefoil were significantly different between groups (all P<.001), while spherical aberration values were not. There was moderate correlation between devices for trefoil (r=0.475 to 0.652), coma (r=0.574 to 0.651), and spherical aberration (r=0.483) and a strong correlation for total cornea RMS (r=0.817). There was no directional bias between groups. The 95% limits of agreement for absolute values was 0.039μm for trefoil at 30 degrees, 0.405μm for trefoil at 0 degree, 0.553μm for horizontal coma, 0.545μm for vertical coma, 0.318μm for spherical aberration, and 0.617μm for RMS. A Scheimpflug imaging device and dual Scheimpflug-Placido imaging device generated statistically different values for total cornea HOAs; however, the correlation between devices was moderate to strong and there was reasonable agreement in all measures for normal eyes. Based on these findings, the devices appear functionally equivalent for clinical use, although caution is warranted for outcomes-based research protocols that report HOAs.

Predictor of thermal aberrations via particle filter for online compensation

In optical lithography, aberrations induced by lens heating effects of a projection lens lead to degradation of imaging quality. In order to compensate for thermal aberrations, it is crucial to apply an accurate method for thermal aberration prediction. An effective and accurate method for thermal aberration prediction is proposed. A double exponential model is modified in respect of the timing of exposure tools, and a particle filter is used to adjust the double exponential model. Parameters of the model are updated recursively pursuant to the aberration data measured during the exchange of wafers. The updated model is used to predict thermal aberrations during the following exposure of wafers. The performance of the algorithm is evaluated by the simulation of a projection lens for argon fluoride lithography. Simulation results show that predictive errors of primary defocus and astigmatism are significantly reduced, and the mean value of wavefront error in the whole field of view is reduced by about 30% in a vertical line/space pattern. The proposed method is easily adaptable to different types of aberration measurement error.

Study on low-order aberration measurements of large-aperture flats based on scanning pentaprism technology.

Pentaprism scanning technology (PPS) is an absolute testing method that has the advantages of a simple structure and absolute testing without an extra reference flat, as well as being able to provide in situ surface measurements, and more. It plays an important role in the manufacturing process of large flat mirrors. For calibrating the PPS's uncertainty, this paper describes a multi-mode scanning method to implement the measurement of low-order aberrations and introduces the concept of an autocorrelation coefficient to evaluate the data processing progress. These improvements were applied to the measurement of a large flat mirror (1630mm in diameter), which demonstrates that the measuring uncertainty of PPS can be about 20nm rms. Furthermore, in regard to the special requirements of M3MP, the prototype mirror of M3M (the tertiary mirror) in the Thirty Meter Telescope project with a non-circular aperture, we analyzed the slope distribution of low-order aberrations, power, and astigmatism. The sample route lines of PPS are then reorganized and a new data process algorithm is implemented. This work was performed in order to improve the PPS's performance in measuring low-order aberrations of large flat mirrors.

Comparison of higher order wavefront aberrations with four aberrometers.

Purpose:To evaluate the agreement of selected higher order aberration measurements between aberrometers based on three different wavefront technologies.Methods:Twenty-three eyes of 23 participants were compared between Zywave, OPD-Scan III, and iDesign aberrometers, for total ocular aberrations. Participants were between 19 and 69 years of age, and exclusion criteria were previous ocular surgery or trauma, contact lens wear within the preceding 2 weeks, and ocular or systemic disease. Corneal aberrations were compared between the OPD-Scan III and GALILEI™ G2 aberrometers. Zernike coefficients of vertical and oblique trefoil, vertical and horizontal coma, and spherical aberration were analyzed in R software.Results:In all, 276 scans were captured in total, with a male-to-female ratio of 11:12. Total ocular vertical coma [mean difference (MD) = 0.026 μm, P < 0.005], vertical trefoil (MD = 0.033 μm, P < 0.05), and spherical aberration (MD = 0.022 μm, P < 0.05) differed significantly between the iDesign and OPD-Scan III. Differences in total vertical (MD = 0.072 μm, P < 0.05) and oblique trefoil (MD = 0.058 μm, P < 0.05) were demonstrated between the Zywave and OPD-Scan III, and spherical aberration (MD = 0.030 μm, P < 0.005) between iDesign and Zywave. iDesign corneal horizontal coma (MD = 0.025 μm, P < 0.05) and spherical aberration (MD = 0.043 μm, P < 0.005) measurements were significantly different between the GALILEI™ G2 and the OPD-Scan III.Conclusion:Zywave, iDesign, and OPD-Scan III, and GALILEI™ G2 and OPD-Scan III may be used interchangeably for their total ocular and corneal wavefront functions, respectively; however, care must be taken if using these devices for guiding ablation or monitoring corneal disease.

Testing and characterization of challenging optics and optical systems with Shack Hartmann wavefront sensors

The Shack-Hartman wavefront sensor is a common metrology tool in the field of laser, adaptive optics and astronomy. However, this technique is still scarcely used in optics and optical system metrology. With the development of manufacturing techniques and the increasing need for optical characterization in the industry, the Shack-Hartmann wavefront sensor emerges as an efficient complementary tool to the well-established Fizeau interferometry for optical system metrology. Moreover, the raise of smart vehicles equipped with optical sensors and augmented reality, the optical characterization of glass and transparent flat materials becomes an issue that can be addressed with Shack-Hartmann sensors. Aberration measurements of challenging optics will be presented such as optical filters, thin flat optics, aspheric lenses and large optical assemblies.

基于差分空间像主成分分析的偏振像差检测方法

基于差分空间像主成分分析的偏振像差检测方法