Residual Wavefront Aberrations Research Articles

Multilevel synergically controlling wavefront correction of a high-power slab laser system.

We present a multilevel synergically controlling wavefront correction method that can apply in a slab laser system. To fully utilize the response frequency and the stroke of actuators of the single deformable mirror (DM), we design a set of multilevel wavefront correction devices to reduce the root-mean square of wavefront aberration before the DM. As the wavefront of slab geometry solid-state lasers mainly consists of fourth and longitudinally distributed aberration, such as 5th, 9th, and 14th orders of Legendre polynomials. We design a precompensating level of the aberration with a slow-drift mirror, fast-steer mirror, one-dimensional adjustable slab-aberration compensator, and beam-shaping system to reduce these orders of wavefront aberration with low spatial resolution and large stroke. As the controlling bandwidth of different devices is diverse, the coupling oscillation between the precompensating level and adaptive optics (AO) level occurs, then we develop the multilevel synergically control to address the coupling. With the precompensating level, the experimental result shows the residual wavefront aberration of the slab laser is compensated well by the AO level effectively within the compensating capability. We clean up a 9.8kW slab laser system with the beam quality β of far-field focus spots improved from 17.71 to 2.24 times the diffraction limit.

Computational analysis of retinal image quality with different contact lens designs in keratoconus.

To determine 1) the relative differences in optical quality of keratoconic eyes fitted with four routinely used CL designs and 2) the Zernike coefficients in the residual wavefront aberration map that may be responsible for differences in the optical quality of keratoconic eyes fitted with these CLs. Wavefront aberrations over a 3-mm pupil diameter were measured without and with Kerasoft IC®, Rose K2®, conventional spherical Rigid Gas Permeable (RGP), and Scleral CLs in 15 mild to moderate keratoconic eyes (20 - 28years) and under unaided viewing in 10 age-similar non-contact lens wearing controls. The resultant through-focus curves constructed for the logarithm of Neural Sharpness (logNS) Image Quality (IQ) metric were quantified in terms of peak value, best focus, and depth of focus. Sensitivity analyses determined the impact of the residual Zernike coefficients of keratoconic eyes fitted with CLs on the IQ of controls at emmetropic refraction. The peak IQ and depth of focus were similar with Rose K2®, conventional RGP, and Scleral CLs (p>0.05, for all) but significantly better than Kerasoft IC® CLs (p<0.01 for all). Best focus was similar across all four CLs (p>0.2 for all). However, the IQ parameters of all the lenses remained significantly poorer than the controls (p<0.01, for all). The IQ of the controls dropped to keratoconic levels with induced residual lower-order Zernike terms and 3rd-order coma across all lenses in the sensitivity analysis (p<0.001). IQ of keratoconic eyes remain suboptimal with routinely dispensed CL designs, largely due to residual lower-order aberrations and coma, all relative to the controls. The performance drop appears greater for the Kerasoft IC® CL relative to the other CL designs. These results may provide the optical basis for psychophysical spatial visual performance reported earlier across these four CL designs for keratoconus.

Wavefront aberrations caused by biomechanical effects after Small Incision Lenticule Extraction (SMILE) based on finite element analysis

To examine wavefront aberrations induced by biomechanical effects after Small Incision Lenticule Extraction (SMILE) surgery. The three-dimensional (3D) finite element models of the human eye were established. By loading the intraocular pressure (IOP), the displacement of the anterior and posterior surface of the cornea was calculated. Then the displacement was converted into the wavefront aberrations by wave-surface fitting. The results showed that the induced wavefront aberrations were noticeable from biomechanical effects after SMILE surgery. The induced higher-order aberrations from the anterior corneal surface included spherical aberration, y-Trefoil, and x-Tetrafoil. Spherical aberration was positively correlated with corrected diopter (D), but x-Tetrafoil and y-Trefoil remained stable. The induced wavefront aberrations from the posterior corneal surface were smaller than those from the anterior corneal surface, and some of the aberrations compensated each other. With IOP increased, defocus and x-Tetrafoil from the anterior corneal surface increased, while y-Trefoil and spherical aberration decreased. The IOP only affected defocus from the posterior corneal surface. In addition, the incision size also had a distinct impact on primary x-astigmatism and x-Trefoil from the anterior corneal surface, and it had a smaller effect on the aberrations from the posterior corneal surface. Therefore, the biomechanical effects increased residual wavefront aberrations after SMILE refractive surgery.

High-precision co-phase method for segments based on a convolutional neural network

In order to achieve the resolution comparable to the resolution of a monolithic primary mirror telescope and make the imaging quality of the imaging system reach or approach to the diffraction limit, the submirrors of the segments telescope should ensure co-phase splicing. To solve the problem of phase error detection, a high-precision piston error detection method is proposed based on convolutional neural network (CNN). By setting a mask with a sparse multi-subpupil configuration on the exit pupil of the imaging system, a point spread function (PSF) image dataset that is extremely sensitive to the piston error is constructed. According to the characteristics of this dataset, a high-performance CNN model is built. And the best detection range of CNN is tested. The simulation results show that a single network can accurately output the piston error of one or more submirrors in the capture range slightly less than one wavelength. When the single network is applied to the six-submirror imaging system, the detection precision of the piston error reaches an RMS value of 0.0013&lt;i&gt;λ&lt;/i&gt; (here, RMS stands for root mean square). And the method has good robustness to residual tip-tilt error, wavefront aberration, and CCD noise, light source bandwidth. The method is simple and fast, and can be widely used to detect the piston error of the segments.

Modeling refractive correction strategies in keratoconus.

This work intends to determine the optimal refractive spectacle and scleral lens corrections for keratoconus patients using the visual Strehl (VSX) visual image quality metric and the SyntEyes models with the synthetic biometry of 20 normal eyes and 20 keratoconic eyes. These included the corneal tomography and intraocular biometry. A series of virtual spherocylindrical spectacle and scleral lens corrections spanning the entire phoropter range were separately applied to each eye, followed by ray tracing to determine the residual wavefront aberrations and identify the correction with the highest possible VSX (named a “focus”). To speed up calculations, a smart scanning algorithm was used, consisting of three consecutive scans over increasingly finer dioptric grids. In the dioptric space, the VSX pattern for normal eyes considered over the correction range for either spectacle or scleral lens corrections resembled an hourglass with one distinct focus and a quick drop in VSX away from that focus. For 18 of the 20 keratoconic eyes, the spectacle-corrected VSX pattern resembled a shell that in 9 of the 20 cases showed two foci separated by a large dioptric distance (13.3 ± 4.9 diopters). In keratoconic eyes, scleral lenses also produced hourglass patterns, but with a VSX lower than in normal eyes. The hourglass pattern in dioptric space shows how, in normal eyes, the refracting process automatically funnels practitioners toward the optimal correction. The shell patterns in keratoconus, however, present far more complexity and, possibly, multiple foci. Depending on the starting point, refracting procedures may lead to a local maximum rather than the optimal correction.

Theoretical Analysis of Wave-Front Aberrations Induced from Conventional Laser Refractive Surgery in a Biomechanical Finite Element Model.

PurposeTo examine the biomechanical effects-induced wave-front aberrations after conventional laser refractive surgery.MethodsA finite element model of the human eye was established to simulate conventional laser refractive surgery with corrected refraction from –1 to –15 diopters (D). The deformation of the anterior and posterior corneal surfaces was obtained under the intraocular pressure (IOP). Then, the surface displacement was converted to wave-front aberrations.ResultsFollowing conventional refractive surgery, significant deformation of the anterior and posterior corneal surfaces occurred because of the corneal biomechanical effects, resulting in increased residual wave-front aberrations. Deformation of the anterior surface resulted in a hyperopic shift, which was significantly increased with the increasing refractive correction. The residual high-order aberrations consisted of spherical aberration, vertical coma, and y-trefoil. Spherical aberration was significantly positively correlated to enhanced refraction correction. The effect of posterior corneal surface on induced wave-front aberration was less than the anterior corneal surface. The IOP slightly affects the postoperative defocus, coma, and spherical aberration. When treatment decentration occurred during the procedure, the hyperopic shift decreased as the eccentricity increased. Treatment decentration had a significant impact on the spherical aberration and the coma. In addition, the ocular tissue elasticity played a key role in hyperopic shift, whereas it had little effect on the other aberrations.ConclusionsAmong the many factors that affect high-order aberrations after conventional laser refractive surgery, the alterations in corneal morphology caused by biomechanical effects must be considered, as they can lead to an increase in postoperative residual wave-front aberrations.

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

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.

Use of focus measure operators for characterization of flood illumination adaptive optics ophthalmoscopy image quality.

Adaptive optics flood illumination ophthalmoscopy (AO-FIO) allows imaging of the cone photoreceptor in the living human retina. However, clinical interpretation of the AO-FIO image remains challenging due to suboptimal quality arising from residual uncorrected wavefront aberrations and rapid eye motion. An objective method of assessing image quality is necessary to determine whether an AO-FIO image is suitable for grading and diagnostic purpose. In this work, we explore the use of focus measure operators as a surrogate measure of AO-FIO image quality. A set of operators are tested on data sets acquired at different focal depths and different retinal locations from healthy volunteers. Our results demonstrate differences in focus measure operator performance in quantifying AO-FIO image quality. Further, we discuss the potential application of the selected focus operators in (i) selection of the best quality AO-FIO image from a series of images collected at the same retinal location and (ii) assessment of longitudinal changes in the diseased retina. Focus function could be incorporated into real-time AO-FIO image processing and provide an initial automated quality assessment during image acquisition or reading center grading.

Model-based adaptive non-null interferometry for freeform surface metrology

A model-based adaptive non-null interferometry (MANI) is proposed for steep optical freeform surfaces in situ testing. The deformable mirror (DM) affording the flexible compensation is monitored with the beam in the interferometer by a wavefront sensor. The residual wavefront aberration in the non-null interferogram is eliminated by the multi-configuration ray tracing algorithm based on the system model, especially the DM surface model. The final figure error can be extracted together with the surface misalignment aberration correction. Experiments proving the feasibility of the MANI are shown.

Optical design of a null test of a synthetic reflective mirror based on the subaperture test method

Machining multiple mirror surfaces on one common substrate during the fabrication of off-axis three-mirror or four-mirror optical systems can take less time and drastically improve the alignment efficiency. However, the difficulty of the surface test remains the same. We theoretically propose a subaperture test method to carry out the null test of two mirrors on the synthetic reflective mirror. Specifically, we design a special zoom null lens and selectively use its subaperture wavefront aberrations of different configurations to nullify the surface normal wavefront aberrations of the according mirrors on the synthetic reflective mirror. The proposed method is verified by simulating the null test process of a synthetic reflective mirror integrating an off-axis high-order primary mirror (PM) and a coaxial high-order tertiary mirror (TM) of one off-axis three-mirror system, with the consideration of the fabrication and alignment errors. Simulation results show that, within a limited range of feasible tolerances, the residual wavefront aberration is 0.033λ root mean square (RMS) for the PM and 0.025λ RMS for the TM, at a wavelength of 1064 nm.

Novel multiple field of view detection method for the off-axis reflection zoom optical system

In order to study the computer-aided alignment for the off-axis reflective zoom optical system, the wavefront aberration of the off-axis reflective zoom system across the field of view needs to be detected. Obtaining the wavefront aberration across the field of view could improve the accuracy of the computer-aided alignment for the off-axis reflective zoom optical system. Restricted by the current wavefront aberration detection technology, only the wavefront aberration at a field degree of 0 could be detected. To solve this problem, a new method to detect the wavefront aberration of off-axis reflective zoom system across the field of view is proposed. According to the traditional autocollimation interferometry method, we improve the detection method by substituting the scan of standard plane mirror with the deformable mirror, replacing the interferometer with Shark-Hartmann sensor and employing the accurately calibrated laser source array to realize the wavefront aberration detection at multiple field of view simultaneously. The simulation shows that the residual wavefront aberration root-mean-square values after compensating for the deformation mirror in the following 6 fields of view (0, 3), (0, 4.2), (0, 5.5), (0, 7), (0, 9.8), and (0, 14) are 0.00039, 0.00075, 0.00024, 0.00017, 0.00053, and 0.0057, respectively. It shows that the detection method we proposed is suitable for the computer-aided alignment technology for the off-axis reflective zoom system.

Improvements on adaptive optics control approaches: experimental tests of wavefront correction forecasting

The FORS (closed loop forecasting system) control algorithm has been already successfully applied to improve the efficiency of a simulated adaptive optics (AO) system. To test its performance in real conditions, we implemented this algorithm in a hardware AO demonstrator, introducing controlled aberrations into the system. We present here the results of introducing into the system both a simple periodic defocus aberration and a real open loop defocus time sequence acquired at the vacuum tower telescope solar telescope. In both cases, FORS yields a significant performance increase, improving the stability of the system in closed-loop conditions and decreasing the amplitude of the residual uncorrected wavefront aberrations.

Contrast Sensitivity Function after Correcting Residual Wavefront Aberrations during RGP Lens Wear

To investigate the effect on the contrast sensitivity function (CSF) of correcting the residual wavefront aberrations in myopic and keratoconic subjects wearing rigid gas permeable (RGP) contact lenses. Seventeen eyes of 16 myopic subjects and 20 eyes of 19 keratoconic subjects were included in this study. All eyes were habitually corrected with RGP lenses. The residual aberrations of the RGP lens-wearing eyes were compensated by an adaptive optics (AO) system. The contrast sensitivities were measured through a 4-mm artificial pupil at spatial frequencies of 2, 4, 8, 16, and 32 cycles per degree (cpd) during RGP lens wear for the myopic and keratoconic groups, respectively. The CSF measurements were repeated with and without AO correction. Comparisons of contrast sensitivity at all spatial frequencies with and without AO correction were performed respectively for the myopic and keratoconic groups during RGP lens wear. In the myopic RGP lens-wearing group, the differences in contrast sensitivity at each spatial frequency, with and without AO correction, were not significant (all p values > 0.05). In the keratoconic RGP lens-wearing group, the contrast sensitivities at all spatial frequencies with AO correction were higher than those without AO correction, but differences only at the low (2 cpd) and intermediate (4, 8, and 16 cpd) spatial frequencies were significant (p = 0.039, 0.005, 0.001, and 0.007). The residual aberrations significantly reduced the contrast sensitivities at low and intermediate spatial frequencies for keratoconic RGP lens-wearing eyes but did not have any effect on the CSF for the myopic RGP lens-wearing eyes. Developing techniques that could more completely correct the wavefront aberrations may improve visual performance in keratoconus.

The influence of the aspheric profiles for transition zone on optical performance of human eye after conventional ablation

The analysis in the impact of transition zone on the optical performance of human eye after laser refractive surgery is important for improving visual correction technology. By designing the ablation profiles of aspheric transition zone and creating the ablation profile for conventional refractive surgery in optical zone, the influence of aspheric transition zone on residual aberrations was studied. The results indicated that the ablation profiles of transition zone had a significant influence on the residual wavefront aberrations. For a hyperopia correction, the profile #9 shows a larger induced coma and spherical aberration when the translation of the centre of pupil remains constant. However, for a myopia astigmatism correction, the induced coma and spherical aberration in profile #1 shows relatively larger RMS values than those in other profiles. Therefore, the residual higher order aberrations may be decreased by optimizing ablation profiles of transition zone, but they cannot be eliminated. In order to achieve the best visual performance, the design of ablation pattern of transition zone played a crucial role.

Adaptive optics optical coherence tomography forin vivomouse retinal imaging

Small animal models of retinal diseases are important to vision research, and noninvasive high resolution in vivo rodent retinal imaging is becoming an increasingly important tool used in this field. We present a custom Fourier domain optical coherence tomography (FD-OCT) instrument for high resolution imaging of mouse retina. In order to overcome aberrations in the mouse eye, we incorporated a commercial adaptive optics system into the sample arm of the refractive FD-OCT system. Additionally, a commercially available refraction canceling lens was used to reduce lower order aberrations and specular back-reflection from the cornea. Performance of the adaptive optics (AO) system for correcting residual wavefront aberration in the mice eyes is presented. Results of AO FD-OCT images of mouse retina acquired in vivo with and without AO correction are shown as well.

Effect of pupil size on residual wavefront aberration with transition zone after customized laser refractive surgery

The analysis of the change in residual wavefront aberrations after laser refractive surgery is important for the development of visual correction technology. Based on the ablation profile for wavefront-guided refractive surgery including optical zone and transition zone, the effect of pupil size on residual wavefront aberrations was studied. The research revealed that the optical zone to pupil ratio had a significant influence on the residual wavefront aberrations. The residual spherical aberration and coma were obviously larger than other individual Zernike higher-order terms when pupil diameter was larger than the optical zone size, and they increased rapidly as the pupil size increased. In addition, when the ablation zone diameter was kept constant, the residual higher-order aberrations increased rapidly as the blend coefficient increased for a 6 mm or 7 mm pupil. Furthermore, the residual higher-order aberrations with treatment decentration were distinctly larger than those without decentration. In the achievement of the best postoperative visual performance, the design of ablation profile played a crucial role in decrease of the residual wavefront aberrations after refractive surgery, especially optical zone size and the ablation pattern of transition zone.

Comparison of aberrations after standard and customized refractive surgery

To detect possible differences in residual wavefront aberrations between standard and customized laser refractive surgery based on mathematical modeling, the residual optical aberrations after conventional and customized laser refractive surgery were compared according to the ablation profile with transition zone. The results indicated that ablation profile has a significant impact on the residual aberrations. The amount of residual aberrations for conventional correction is higher than that for customized correction. Additionally, the residual aberrations for high myopia eyes are markedly larger than those for moderate myopia eyes. For a 5 mm pupil, the main residual aberration term is coma and yet it is spherical aberration for a 7 mm pupil. When the pupil diameter is the same as optical zone or greater, the magnitudes of residual aberrations is obviously larger than that for a smaller pupil. In addition, the magnitudes of the residual fifth or sixth order aberrations are relatively large, especially secondary coma in a 6 mm pupil and secondary spherical aberration in a 7 mm pupil. Therefore, the customized ablation profile may be superior to the conventional correction even though the transition zone and treatment decentration are taken into account. However, the customized ablation profile will still induce significant amount of residual aberrations.

高功率激光驱动器波前残余像差研究

高功率激光驱动器波前残余像差研究

Robert H. Koch's Work on Lightweight Medium-Aperture Mirrors

After a visit by Peter Waddell from the University of Strathclyde, Glasgow, UK in 1991, Robert H. Koch launched a program at the University of Pennsylvania to build lightweight pneumatic membrane mirrors, initially for balloon flight observations where weight is at a premium. Mirror cells were fabricated from sizes 0.18 m to 1.77 m, and experiments conducted to characterize the mirror figure and stability. Most of the work stopped after Prof. Koch's retirement in 1996 until 2006 when the authors expressed an interest in building an array of medium-aperture portable telescopes. The program restarted in earnest at Gravic, Inc. in Malvern, PA in 2008 with Koch using his extensive observational astronomy experience to guide the fabrication of a fully operational 1.07 m membrane mirror telescope with an optical tube assembly weighing under 45 Kg. Residual wavefront aberrations remediation resulted in Koch and the authors investigating membrane tensioning techniques with different cell designs, active secondary wavefront correction, photometric algorithms for aberrated images, and the use of additional lightweight mirror substrates from the Alt-Az Initiative Group, such as foamed glass. The best result for the lightweight mirrors was a point spread function spot size of several arc seconds. A lightweight 1.6 m cast aluminum cell alt-az telescope was subsequently designed by Koch and the authors for prime focus use.

Stabilized high-accuracy correction of ocular aberrations with liquid crystal on silicon spatial light modulator in adaptive optics retinal imaging system

We studied the long-term optical performance of an adaptive optics scanning laser ophthalmoscope that uses a liquid crystal on silicon spatial light modulator to correct ocular aberrations. The system achieved good compensation of aberrations while acquiring images of fine retinal structures, excepting during sudden eye movements. The residual wavefront aberrations collected over several minutes in several situations were statistically analyzed. The mean values of the root-mean-square residual wavefront errors were 23-30 nm, and for around 91-94% of the effective time the errors were below the Marechal criterion for diffraction limited imaging. The ability to axially shift the imaging plane to different retinal depths was also demonstrated.