Spherical Aberration Compensation Research Articles

Spherical Aberration and Scattering Compensation in Microscopy Images through a Blind Deconvolution Method.

The optical quality of an image depends on both the optical properties of the imaging system and the physical properties of the medium the light passes while travelling from the object to the image plane. The computation of the point spread function (PSF) associated to the optical system is often used to assess the image quality. In a non-ideal optical system, the PSF is affected by aberrations that distort the final image. Moreover, in the presence of turbid media, the scattering phenomena spread the light at wide angular distributions that contribute to reduce contrast and sharpness. If the mathematical degradation operator affecting the recorded image is known, the image can be restored through deconvolution methods. In some scenarios, no (or partial) information on the PSF is available. In those cases, blind deconvolution approaches arise as useful solutions for image restoration. In this work, a new blind deconvolution method is proposed to restore images using spherical aberration (SA) and scatter-based kernel filters. The procedure was evaluated in different microscopy images. The results show the capability of the algorithm to detect both degradation coefficients (i.e., SA and scattering) and to restore images without information on the real PSF.

Comprehensive holographic parallel beam modulation inside material based on automatic differentiation

Holographic beam modulation is widely applied in optical tweezers, hard-brittle material marking, high-density storage, etc. To generate high-fidelity arbitrary 3-dimensional (3D) parallel multifoci inside the material, the spherical aberration compensated automatic differentiation (SACAD) algorithm is presented. All polarization components are included and the spherical aberration compensation is embedded in the physical model. The technique of automatic differentiation is used in the error backpropagation procedure, ensuring efficient parallel computing of pixel-by-pixel gradients. In several simulation tests, the root mean square errors of the generated 3D multifoci distributions are all less than 0.01 and the diffraction efficiencies are all beyond 90%, outperforming the results of the established algorithms. In the experiments, we have verified the advantage of SACAD algorithm in complicated 3D internal marking with spherical aberration compensation. Since the SACAD algorithm can achieve high fidelity and efficiency phase retrieval with a straightforward procedure, it has the potential to become a well-received solution for internal parallel beam modulation.

Understanding the limits of remote focusing.

It has previously been demonstrated in both simulation and experiment that well aligned remote focusing microscopes exhibit residual spherical aberration outside the focal plane. In this work, compensation of the residual spherical aberration is provided by the correction collar on the primary objective, controlled by a high precision stepper motor. A Shack-Hartmann wave front sensor is used to demonstrate the magnitude of the spherical aberration generated by the correction collar matches that predicted by an optical model of the objective lens. The limited impact of spherical aberration compensation on the diffraction limited range of the remote focusing system is described through a consideration of both on-axis and off-axis comatic and astigmatic aberrations, which are an inherent feature of remote focusing microscopes.

Spherical lens aberration minimization method for short-range free-space light transmission

Spherical aberrations of lenses lead to increased spot radii on the focal plane. Several methods, such as optimizing thickness and radii or building lens groups, are known to minimize these spherical aberrations. Here, an innovative method for spherical aberration minimization is introduced; it can be used for short-range free-space optical communication systems, such as unit power afocal relay trains, lens waveguides, and periodic lens systems. This spherical aberration compensation principle is based on the combination of two identical spherical convex lenses at an optimal distance. Due to the higher refractive power for rays with an larger axis distance, rays from the outer area of the first lens intersect the inner area of the second lens, and vice versa. With this setup, the radial refractive power deviation of the two lenses compensate each other. Analytic calculations and numerical simulations are done to confirm this behavior, and measurements using two symmetric spherical lenses with polymer optical fibers as light feed confirm the calculations. Simulations and measurements show a very good matching behavior except for an unknown systematic error. At a lens distance of 300 mm, the optical attenuation decreased by ∼2 dB compared with a very small lens distance. This leads to the conclusion that this proposed spherical aberration minimization method works as theoretically predicted.

Stealth dicing of 1-mm-thick glass with aberration-free axial multi-focus beams.

Laser stealth dicing can realize material separation with negligible surface damage, but severe aberrations in thick materials degrade processing quality. This Letter presents a nonlinear point-to-point transformation method combined with spherical aberration compensation to achieve aberration-free axial multi-focus beams. The focus peak intensity increases 7 times at a depth of 0.5 mm after spherical aberration compensation, and reaches 44 times at 3.5 mm. Spherical aberration compensation experiments showed that the width of the heat-affected zone remains almost unchanged at different depths inside the glass, and stealth dicing experiments for 1-mm-thick glass demonstrated that aberration-free 1-focus, 2-foci, and 3-foci stealth dicing can be successfully realized.

Flexible, video-rate, and aberration-compensated axial dual-line scanning imaging with field-of-view jointing and stepped remote focusing

Parallel dual-plane imaging with a large axial interval enables the simultaneous observation of biological structures and activities in different views of interest. However, the inflexibility in adjusting the field-of-view (FOV) positions in three dimensions and optical sectioning effects, as well as the relatively small effective axial range limited by spherical aberration, have hindered the application of parallel dual-plane imaging. Herein, we propose a flexible, video-rate, and defocus-aberration-compensated axial dual-line scanning imaging method. We used a stepped mirror to remotely generate and detect dual axial lines with compensation for spherical aberration and FOV-jointing to rearrange into a head-to-head line for high-speed optical sectioning acquisition. The lateral and axial positions of the two FOVs could be flexibly adjusted before and during imaging, respectively. The method also allows the adjustment of optical sectioning effects according to specific experimental requirements. We experimentally verified the consistent imaging performance over an axial range of 300 μm. We demonstrated high throughput by simultaneously imaging Brownian motions in two 250 μm × 250 μm FOVs with axial and lateral intervals of 150 μm and 240 μm, respectively, at 24.5 Hz. We also showed potential application in functional imaging by simultaneously acquiring neural activities in the optic tectum and hindbrain of a zebrafish brain. The proposed method is, thus, advantageous compared to existing parallel dual-plane imaging and potentially facilitates intravital biological study in large axial range.

Precise 3D computer-generated holography based on non-convex optimization with spherical aberration compensation (SAC-NOVO) for two-photon optogenetics.

Computer-generated holography (CGH) has been adopted in two-photon optogenetics as a promising technique for selective excitation of neural ensembles. However, 3D CGH by nonconvex optimization, the state of art method, is susceptible to imprecise axial positioning, due to the quadratic phase approximation in 3D target generation. Even though the misplacement of targets in conventional CGH can be solved by pre-calibration, it still suffers from low efficiency and poor axial resolution of two-photon excitation. Here, we propose a novel CGH method based on non-convex optimization with spherical aberration compensation (SAC-NOVO). Through numerical simulations and two-photon excitation experiments, we verify that SAC-NOVO could achieve precise axial positioning for single and multiple expanded disk patterns, while ensuring high two-photon excitation efficiency. Besides, we experimentally show that SAC-NOVO enables the suppression of dark target areas. This work shows the superiority of SAC-NOVO for two-photon optogenetics.

Aberration-free aspherical in-plane tunable liquid lenses by regulating local curvatures.

Aberration is a long-standing problem of fixed focal lenses and a complicated lens set is usually required to compensate for aberration. It becomes more challenging for tunable lenses. This paper reports an original design of an in-plane optofluidic lens that enables compensation for spherical aberration during the tuning of focal length. The key idea is to use two arrays of electrode strips to symmetrically control the two air/liquid interfaces by the dielectrophoretic effect. The strips work together to define the global shape of the lens interface and thus the focal length, whereas each strip regulates the local curvature of the interface to focus the paraxial and peripheral arrays on the same point. Experiments using a silicone oil droplet demonstrate the tuning of focal length over 500-1400 μm and obtain a longitudinal spherical aberration (LSA) of ∼3.5 μm, which is only 1/24 of the LSA (85 μm) of the spherical lens. Fine adjustment of the applied voltages of strips allows even elimination of the LSA and enabling of the aberration-free tunable lenses. It is the first time that local curvature regulation is used to compensate for the aberration within one in-plane liquid lens. This simple and effective method will find potential applications in lab-on-a-chip systems.

Raman gas analyzer for detecting carbon isotopologues

A Raman gas analyzer for detecting carbon isotopologues with an excitation laser with a power of 5 W, generating at a wavelength of 532 nm, focusable in a waist of 7 μm using a lens with compensation for spherical aberration is presented. The signal is detected by a high-resolution spectrometer with a matrix cooled to -40° C. The program optimization of the system parameters is presented: focusing lens, cuvette windows.

Optical concepts – monofocal, aspheric, toric, multifocal, EDOF

AbstractWe will present an overview of the various optical concepts used in intraocular lenses: while the conventional monofocal lens was designed to provide basic refractive correction, modern aspheric lenses aim to provide better contrast sensitivity by compensation of intrinsic or corneal spherical aberration. Toric lenses were developed to correct corneal astigmatism during cataract surgery. Multifocal lenses aim to provide functional visual acuity at various distance levels. There are basically two concepts of implementing multifocality: those based on refraction and those based on diffraction. Modern extended depth of focus lenses try to fill in the gap between monofocal and multifocal lenses by providing acceptable visual acuity from far distance to intermediate distance.

A review of higher order aberrations of the human eye

Background: This literature review is part of a research study for aberration-correcting soft contact lenses, where wavefront aberrometry was utilised. Aim: This study was conducted as part of a postgraduate research degree by the first author with particular relevance to spherical aberrations in relation to myopia and soft contact lenses, both aberration control and non-control types. Setting: This study reports on a literature review of higher order aberrations. Methods: A comprehensive review of various databases was performed, including PubMed and Google Scholar in terms of aberration control contact lenses and particular customised contact lenses for compensation of spherical aberration in myopia, was performed. Results: Wavefront sensing and Zernike polynomials are increasingly used in optometry and ophthalmology to quantify the wavefronts for an optical system such as the eye, using either lower order (LOA) or higher order aberrations (HOA). Although other mathematical methods are available, zero, 1st and 2nd orders of the Zernike polynomial expansion are LOA. Defocus ( ) and astigmatism ( and ) are 2nd-order modes that usually can be corrected by clinicians using ordinary sphero-cylindrical compensations such as spectacle lenses. Until recently, only LOA were easily correctable by clinicians in optometry and ophthalmology. Higher order aberrations are those modes in the third radial order, n = 3 and higher, which in the past were not correctable. However, HOA contribute to only about 7% of retinal image quality and often go unnoticed by individuals, although in some instances, for example, with keratoconus or after refractive surgery, such aberrations can become more problematic. Today, new treatments are available via specially designed or customised (to an individual) rigid or soft contact lenses that are claimed to reduce or eliminate HOA such as spherical aberration ( ). Conclusion: Although such specially designed or customised contact lenses have some effect on HOA, there are conflicting reports and so further investigation of this intriguing aspect remains necessary.

Tunable liquid lens integrated with aspheric surface

In this paper, we propose and experimentally demonstrate a tunable liquid lens integrated with an aspherical surface for spherical aberration and distortion compensation. Through optimizing the aspherical surface’s morphology, the spherical aberration and distortion can be significantly reduced. The root mean square spot size at focus is distinctly reduced from 55.7μm to 2.095μm after performing optimum optimization. The tunable liquid lens is integrated with the aspheric surface with 6 mm clear aperture and 19.2 mm minimum focal length and demonstrate the improvement in optical performance over the conventional lens without an aspheric surface over a focal length range. Its applications in microscope system and tunable-focus eyeglasses are foreseeable.

A high-beam-quality Nd:YAG rod laser with a VRM and spherical aberration compensation at 400 Hz

A high-beam-quality and high-energy long-pulse laser has been developed with VRM(variable reflectivity mirror)coupling and spherical aberration compensation. The thermal lens and the thermal birefringence are compensated for by the 10 mm DL rod side-pumped laser module. The output mirror employs VRM coupling with R=35% in the center, which presents a energy of 1.04 J at a pulse width of 195 μs and a repetition rate of 400 Hz with a beam quality of M2≈8.4. The spherical aberration compensation improves the beam quality M2 factor to 2.15; the power stability (RMS) is 0.4% at 5 min, and the optical-optical efficiency is 19.7%.

Generation of non-paraxial accelerating beams by active aberration compensation

We demonstrate the generation of non-paraxial accelerating beams by using an objective with an external spherical aberration compensation. A correction phase is applied at an illuminating plane before the objective, and such an aberration-corrected system enables a Fourier transform that translates a proper spatial spectral phase pattern into the desired non-paraxial accelerating beams. The feasibility of the scheme and the quality of the generated beams are further discussed for various conditions. Experimentally, we observe the accelerating beams as well as non-paraxial autofocusing beams following predesigned trajectories generated with such an aberration compensation method, providing an effective and alternative approach for non-paraxial beam shaping.

First results with a new intraocular lens design for the individual correction of spherical aberration

To assess the feasibility of individual compensation of corneal spherical aberration with a custom intraocular lens (IOL). Department of Ophthalmology, Rudolf Virchow Klinikum Glauchau, Glauchau, Germany. Prospective case series. Cataract patients were randomized to receive an individual aberration-correcting IOL (Invidua-aA; Group A) or a standard aspheric aberration-free IOL of otherwise identical design (Aspira-aA; Group B). In Group A, the IOL was designed according to preoperative calculation of the corneal spherical aberration Z(4,0). The aim was to achieve an overall postoperative ocular spherical aberration close to zero. Four weeks and 3months postoperatively, the refraction, visual acuity (far, intermediate, and near distance), photopic and mesopic contrast sensitivities (with and without glare), defocus curve, corneal and ocular spherical aberration, and pupil size were measured. Group A, 57 eyes of 42 patients and Group B, 29 eyes of 27 patients. Preoperatively, there was no difference in corneal spherical aberration between groups (P>.05). Three months postoperatively, residual ocular spherical aberration Z(4,0) was significantly lower in Group A (P<.001). Photopic and mesopic contrast sensitivities (with and without glare) were significantly higher in Group A at most spatial frequencies. Monocular defocus curve and distance, intermediate, and near visual acuity outcomes did not differ significantly between groups. Implantation of a custom monofocal aspheric IOL effectively reduced overall ocular spherical aberration. Clinical outcomes indicate that IOLs with an individual spherical aberration correction improve functional vision, especially contrast sensitivity, compared with standard aberration-free IOLs.

Accurate shape measurement of focusing microstructures in Fourier digital holographic microscopy.

This paper proposes a measurement method of focusing objects with a high gradient shape of a small and large radius of curvature. The measurements are carried out on a Fourier digital holographic microscope with optimized illumination conditions maximizing the usage of the system's numerical aperture. The obtained fringe patterns are the result of interference of deformed spherical object and spherical reference waves. The key elements of the method are the aberration compensation and calibration procedures. They provide accurate reconstruction of the object wave and determination of the focus position of the sample. The shape is calculated in two steps. First, the object wave is reconstructed at the plane of the object focus using single or multiframe phase extraction algorithm and the specialized propagation method. The step includes compensation for spherical aberration. In the second step, the sample shape is computed with the local ray approximation approach. The proposed method is experimentally validated with measurements of challenging, high gradient shapes (convex, concave) of different radiuses of curvature.

Aberration compensation for optical trapping of cells within living mice.

Optical tweezers have been used to trap and manipulate microparticles within living animals. When the optical trap is constructed with an oil-immersion objective, it suffers from spherical aberration. There have been many investigations on the influence of spherical aberration when the particles are trapped in a water medium. However, the dependence of optical force on trapping depth is still ambiguous when the trapped particles are immersed in a high refractive index medium (such as biological tissue, refractive index solution) in experiments. In this paper, the microparticles are immersed in an aqueous solution of glycerol to mimic the cells within biological tissue. As the trapping laser is focused into the specimen, spherical aberration is introduced, degrading the optical trapping performance. It is similar to trapping in water; altering the effective tube length can also compensate for the spherical aberration of the optical trap in a high refractive index medium. Finally, the cells in living mice are trapped by the optical tweezers with the help of spherical aberration compensation.

All-dielectric ultrathin conformal metasurfaces: lensing and cloaking applications at 532 nm wavelength.

Metasurfaces are ideal candidates for conformal wave manipulation on curved objects due to their low profiles and rich functionalities. Here we design and analyze conformal metasurfaces for practical optical applications at 532 nm visible band for the first time. The inclusions are silicon disk nanoantennas embedded in a flexible supporting layer of polydimethylsiloxane (PDMS). They behave as local phase controllers in subwavelength dimensions for successful modification of electromagnetic responses point by point, with merits of high efficiency, at visible regime, ultrathin films, good tolerance to the incidence angle and the grid stretching due to the curvy substrate. An efficient modeling technique based on field equivalence principle is systematically proposed for characterizing metasurfaces with huge arrays of nanoantennas oriented in a conformal manner. Utilizing the robust nanoantenna inclusions and benefiting from the powerful analyzing tool, we successfully demonstrate the superior performances of the conformal metasurfaces in two specific areas, with one for lensing and compensation of spherical aberration, and the other carpet cloak, both at 532 nm visible spectrum.

Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes

Objective: To study the compensation mechanism of aberrations between anterior and posterior corneal surface, and to investigate the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Methods: One hundred and sixty-one subjects (300 eyes) with myopia and myopic astigmatism were recruited randomly. Corneal aberrations (anterior, posterior and total) in three different optical zones (2 mm, 4 mm, and 6 mm) centered on the corneal vertex were assessed with a corneal topographer (Sirius). We also calculated compensation factors (CFs) as a measure of the relative efficiency of the aberration compensation mechanism. Astigmatism was divided into corneal astigmatism and non-corneal astigmatism. Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups. Spearman correlation was applied to analyze the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Results: As the order of the aberrations elevated from the second to the seventh, the RMS values decreased significantly. The larger the optical zone, the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms. At the same time, as the order of the aberrations increased, the predominance of the compensation mechanism was increasingly obvious. Slight compensation of spherical aberration (Z40) was observed in the peripheral. In the center of the analyzing zones (2 mm), compensation mechanism represented in coma (Z3±1), and it disappeared in the peripheral. We detected slight compensation of the corneal astigmatism (Z2±2) in the surrounding zone, although the compensation factors were closed to zero in diverse optical zones. Superposition was found in trefoil (Z3±3) straightly. Nevertheless, a tendency towards compensation was discovered with the enlargement of the optical zones. And the secondary spherical aberration (Z60) behaved compensation continuously. However, similar compensation was discovered between the right eye and left eye in different analyzing optical zones. There were significant correlations between the flattest K values and Z2±2, Z3±3and Z40 in the anterior, posterior and total cornea. It was similar with the steepest K values. When the optical zone expanded to 6 mm, Z3±1 and Z40 significantly decreased with intraocular pressure (rcoma=-0.188, P<0.05. rspherical=-0.147, P<0.05). No correlation was found between various aberrations and central corneal thickness (P>0.05). Conclusions: Compensation dominated in the corneal center, while the percentage decreased gradually as the optical zone extended. Slight compensation in astigmatism and spherical aberration between the anterior and posterior cornea may be benificial to the scotopic visual quality. Corneal aberrations were significantly related to K values and intraocular pressure. (Chin J Ophthalmol, 2016, 52: 840-849).

Beam Quality Management in Multi-Stage Side-Pumped Nd:YAG MOPA Laser Systems

A method of beam quality management in multi-stage Master-oscillator power-amplifier (MOPA) laser systems has been presented. Beam quality always gets worse when a laser beam passes though an amplifier due to the thermally induced aberrations in the intensively pumped gain medium. Numerical calculations show that the spherical aberration (SA) coefficient of the aberrated beam wavefront from the amplifier can change the sign in free space propagation. The wavefront can thus be compensated by another amplifier, which has nearly identical pumping parameters with the first amplifier. A single-pass two-stage side-pumped Nd:YAG amplifier is developed in experiments. The seed beam from the oscillator with 42 W output power and beam quality factor of M 2 = 1.21 is scaled up to 74 W by the first stage of the amplifier, while the beam quality is degraded to M 2 = 1.80. The beam quality is improved to M 2 = 1.30 after the second stage by properly wavefront compensation and the output power is 101 W. Experiments are also carried out with a double-pass one-stage amplifier. The output beam with 84 W power and M 2 = 1.29 is achieved. To our best knowledge, it is the first time that beam quality enhancement in a side-pumped MOPA is demonstrated by SA compensation.