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Characterized by a high resolution, high throughput (large effective area), and large field of view, the Wolter-I microscope is the main grazing incidence imaging device for x-rays and neutrons. It is necessary to estimate the tolerance of surface deformation to achieve the required resolution in typical applications. Traditional tolerance estimation method based on Monte Carlo method required a large random sampling in a given sampling area and has a low efficiency. We derived the transverse ray aberration equations to investigate the image quality degradation caused by principal figure and alignment errors and proposed a line fitting tolerance estimation method. Finally, the figure and alignment error tolerances of a Wolter-I microscope are discussed. [ABSTRACT FROM AUTHOR]

We experimentally investigate the performance of co-optimized hybrid optical-digital imaging systems based on binary phase masks and digital deconvolution for extended depth-of-field (DoF) under narrowband illumination hypothesis. These systems are numerically optimized by assuming a simple generic imaging model. Using images of DoF targets and real scenes, we experimentally demonstrate that in practice, they actually reach the DoF range for which they have been optimized. Moreover, they are shown to be robust against small mask manufacturing errors and residual spherical aberration in the optical system. These results demonstrate that the optical/digital optimization protocol based on generic imaging model can be safely used to design DoF-enhanced imaging systems aimed at real-world applications. [ABSTRACT FROM AUTHOR]

Hypernumerical aperture and polarized illumination are the key technologies of resolution enhancement of lithography. When the numerical aperture reaches 0.85 and above, especially in the immersion lithography, polarization effect must be taken into consideration. The performance of the projection lens needs to be characterized by rigorous polarization aberration. The vector polarization imaging system that is suitable for hypernumerical aperture is established, and the distortion effects introduced by polarization aberration are analyzed. Orientation Zernike polynomials-based method and Pauli-Zernike polynomials-based method are adopted to parameterize the polarization aberration represented by Jones pupil. Critical dimension error, placement error, and normal int. log slope index are introduced as the index to value imaging distortion. The proposed method and analysis conclusion would provide meaningful guidance for projection lens design of lithographic tools. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Point spread function (PSF) engineering has met with lots of interest in various optical imaging techniques, including super-resolution microscopy, microparticle tracking, and extended depth-of-field microscopy. The intensity distributions of the modified PSFs often suffer from deteriorations caused by system aberrations, which greatly degrade the image contrast, resolution, or localization precision. We present an aberration correction method using a spiral-phase-based double-helix PSF as an aberration indicator, which is sensitive and quantitatively correlated to the spherical aberration, coma, and astigmatism. Superior to the routine iterationbased correction methods, the presented approach is iteration-free and the aberration coefficients can be directly calculated with the measured parameters, relieving the computing burden. The validity of the method is verified by both examining the intensity distribution of the conventional Gaussian PSF in three dimensions and observing muntjac skin fibroblast cells. This iteration-free correction method has a potential application in PSF engineering systems equipped with a spatial light modulator. [ABSTRACT FROM AUTHOR]

We present simulation results of hypothetical satellite systems with fifth-order optical aberrations and various fractal apertures. On the image sensor side, we utilized novel metamaterial based image sensors (metaxels). Real physical systems always have some amount of optical aberrations even though electro-optical systems operating in space are generally idealized as diffraction limited in many simulations. Not only Seidel aberrations but also fifth-order aberrations are important in satellite image analyses and here we illustrate the effects of six aberration groups: spherical, linear coma, elliptical coma, oblique spherical, astigmatism-field curvature, and distortion. Our analyses yield optical diffraction and aberration effects all at once. Any combined form of aberrations could be investigated, which constitute an ample dimension for imaging chain and image quality studies. For a λ/2 aberration coefficient, quantitative comparison was provided, and for various fractal aperture cases image chain simulations are performed. Correlation coefficient values for the listed groups of aberration enabled us to quantify significance order of these fifth-order aberrations. Fifth-order distortion was the most dominant aberration affecting the image quality. In addition, we increased the fractal dimension of apertures and obtained smaller degradation in the images. The study ends with Wiener filter restoration results. Peak signal-to-noise ratio and correlation coefficient values for the restored images were higher than corresponding aperture cases as expected. [ABSTRACT FROM AUTHOR]

Mapping flows in vivo is essential for the investigation of cardiovascular pathologies in animal models. The limitation of optical-based methods, such as space-time cross correlation, is the scattering of light by the connective and fat components and the direct wave front distortion by large inhomogeneities in the tissue. Nonlinear excitation of the sample fluorescence helps us by reducing light scattering in excitation. However, there is still a limitation on the signal-background due to the wave front distortion. We develop a diffractive optical microscope based on a single spatial light modulator (SLM) with no movable parts. We combine the correction of wave front distortions to the cross-correlation analysis of the flow dynamics. We use the SLM to shine arbitrary patterns of spots on the sample, to correct their optical aberrations, to shift the aberration corrected spot array on the sample for the collection of fluorescence images, and to measure flow velocities from the cross-correlation functions computed between couples of spots. The setup and the algorithms are tested on various microfluidic devices. By applying the adaptive optics correction algorithm, it is possible to increase up to 5 times the signalto- background ratio and to reduce approximately of the same ratio the uncertainty of the flow speed measurement. By working on grids of spots, we can correct different aberrations in different portions of the field of view, a feature that allows for anisoplanatic aberrations correction. Finally, being more efficient in the excitation, we increase the accuracy of the speed measurement by employing a larger number of spots in the grid despite the fact that the two-photon excitation efficiency scales as the fourth power of this number: we achieve a twofold decrease of the uncertainty and a threefold increase of the accuracy in the evaluation of the flow speed. [ABSTRACT FROM AUTHOR]

Training autonomous vehicles requires lots of driving sequences in all situations. Collecting and labeling these drive scenes is a very time-consuming and expensive process. Currently, it is not possible to reuse these drive scenes with different optical properties, because there exists no numerically efficient model for the transfer function of the optical system. We present a numerical model for the point spread function (PSF) of an optical system that can efficiently model both experimental measurements and lens design simulations of the PSF. The numerical basis for this model is a nonlinear regression of the PSF with an artificial neural network. The novelty lies in the portability and the parameterization of this model. We present a lens measurement series, yielding a numerical function for the PSF that depends only on the parameters defocus, field, and azimuth. By convolving existing images and videos with this PSF, we generate images as if seen through the measured lens. The methodology applies to any optical scenario, but we focus on the context of autonomous driving, where the quality of the detection algorithms depends directly on the optical quality of the used camera system. With this model, it is possible to reuse existing recordings, with the potential to avoid millions of test drive miles. The parameterization of the optical model allows fora method to validate the functional and safety limits of camera-based advanced driver assistance systems based on the real, measured lens actually used in the product. [ABSTRACT FROM AUTHOR]

Impaired oxygen delivery and/or consumption in the retinal tissue underlies the pathophysiology of many retinal diseases. However, the essential tools for measuring oxygen concentration in retinal capillaries and studying oxygen transport to retinal tissue are still lacking. We show that two-photon phosphorescence lifetime microscopy can be used to map absolute partial pressures of oxygen (pO2) in the retinal capillary plexus. Measurements were performed at various retinal depths in anesthetized mice under systemic normoxic and hyperoxic conditions. We used a newly developed two-photon phosphorescent oxygen probe, based on a two-photon absorbing platinum tetraphthalimidoporphyrin, and commercially available optics without correction for optical aberrations of the eye. The transverse and axial distances within the tissue volume were calibrated using a model of the eye's optical system. We believe this is the first demonstration of in vivo depth-resolved imaging of pO2 in retinal capillaries. Application of this method has the potential to advance our understanding of oxygen delivery on the microvascular scale and help elucidate mechanisms underlying various retinal diseases. [ABSTRACT FROM AUTHOR]

In optical lithography tools, thermal aberration of a projection lens, which is caused by lens heating effect, leads to degradation of imaging quality. In addition to in-line feedforward compensation technology, thermal aberration can be reduced by optimizing optical design of a projector. Thermal aberration analysis of a projection lens benefits the optimization of optical design. A model of lens heating effect for a lithographic projector is introduced, which is capable of evaluating the synthetical thermal aberration of a projector as well as analyzing the contribution of an individual optical element. Simulation results by the introduced model show that not only the deformation of lens surface, the variance of refractive index but also the change of optical path, which depends on optical design, should be considered in thermal aberration analysis. The contributions of optical elements at different locations of the projector are also analyzed. Based on the model and the simulation results, an optimization method is proposed. A projector for i-line lithography is optimized by the proposed method. Main aberrations Z5, Z9, and Z17 are reduced by about 40%. The image quality of the lithographic projector in steady state is also improved. [ABSTRACT FROM AUTHOR]

A set of methods in terms of both image processing and gaze estimation for accurate eye tracking is proposed. The eye-tracker used in this study relies on the dark-pupil method with up to 12 corneal reflections and offers an unprecedented high resolution imaging of the pupil and the cornea. The potential benefits of a higher number of glints and their optimum arrangement are analyzed considering distinct light sources configurations with 12, 8, 6, 4, and 2 corneal reflections. Moreover, a normalization factor of the pupil-glint vector is proposed for each configuration. There is a tendency for increasing accuracy with the number of glints, especially vertically (0.47 deg for 12 glints configuration versus 0.65 deg for 2 glints configuration). Besides the number of corneal reflections, their arrangement seems to have a stronger effect. A configuration that minimizes the interference of the eyelids with the corneal reflections is desired. Finally, the normalization of the pupil-glint vectors improves the vertical eye tracking accuracy up to 43.2%. In addition, the normalization also limits the need for a higher number of light sources to achieve better spatial accuracy. [ABSTRACT FROM AUTHOR]

This work presents the exact analytical formula for calculation of the longitudinal chromatic aberration of a lens, in contrast with the approximate nature of the traditional approach based only on the dispersion of the optical material. This formula additionally takes into account the radii of curvature of the lens surfaces, lens thickness, object and image distances, and the chromatic aberration of the previous optical system. The presented formula is used for the derivation of rigorous equations for color correction of simple lens systems. To test them, this work presents examples of achromatic and apochromatic lenses that are designed by solving these equations. These results prove the usefulness of the presented approach for color correction and open the way for a broad and rigorous study of chromatic aberrations in various optical systems. [ABSTRACT FROM AUTHOR]

Focus-tunable liquid lenses are used in various applications due to their compact size, light weight, low power consumption, and cost effectiveness. They have the potential for use in space applications, such as focus compensation, optical communications, and imaging systems. However, liquid lenses have not yet been evaluated for use in the space environment. This work focuses on characterizing operational differences of commercially available liquid lenses from Corning Varioptic and Optotune between Earth gravity, microgravity, and hypergravity environments. Results show a linear drift in the tip/tilt of 0.80 and 4.20 mrad going from 1 to 0 g for the Corning Varioptic A-39N0 lens and Optotune EL-16-40-TC-VIS lens, respectively, with lower optical aberrations in microgravity. Additionally, a significant but small increase in focal power going from 1 to 0 g by 0.02 D is observed for the Optotune lens. No significant change in focal power is observed for the Corning Varioptic lens tested in this experiment. Additionally, potential multi-beam interference is observed in defocus patterns of the Corning Varioptic lens tested during the experiment. [ABSTRACT FROM AUTHOR]

We study a simulation method that uses the Wigner distribution function to incorporate wave optical effects in an established framework based on geometrical optics, i.e., a ray tracing engine. We use the method to calculate point spread functions and show that it is accurate for paraxial systems but produces unphysical results in the presence of aberrations. The cause of these anomalies is explained using an analytical model. [ABSTRACT FROM AUTHOR]

A two-frequency laser scanning confocal fluorescence microscope (TF-LSCFM) based on intensity modulated fluorescence signal detection was proposed. The specimen-induced spherical aberration and scattering effect were suppressed intrinsically, and high image contrast was presented due to heterodyne interference. An improved axial point spread function in a TF-LSCFM compared with a conventional laser scanning confocal fluorescence microscope was demonstrated and discussed. [ABSTRACT FROM AUTHOR]

An attempt has been made to propose a passive flexure-based semikinematic optimized mounting design for mirror fixing devices (MFDs) to mount spacecraft mirrors made of brittle materials, especially for high aspect ratio mirrors with low available space for mounting in satellites. The traditionally used tangent cantilever spiders occupy a lot of space and are suitable only for small mirrors. Similarly, the efficiency of flexural bipods is lost if not placed 120 deg apart, which is not possible in high aspect ratio mirrors. Two mounting configurations, one with collinear MFDs and the other with staggered MFDs, have been studied. An optimization problem is set up with dimensions of the proposed design as design variables and constraints imposed on structural performance of the mirror assembly. Investigations indicate that both configurations have potential applications in spacecrafts as they have provided feasible results and have satisfactory optical performance as well. [ABSTRACT FROM AUTHOR]

We report the results of experimental studies on cardiac implants using a Raman spectroscopy method (RS). Raman spectra characteristics of leaves and walls of cardiac implants were obtained; the implants were manufactured by protocols of detergent-enzymatic technique (DET) and biological, detergent-free (BIO) decellularization, using detergents (group DET) or a detergent-free, nonproteolytic, actin-disassembling regimen (BIO). There were input optical coefficients that allowed us to carry out evaluation of the protocols of DET and BIO decellularization on the basis of the concentrations of glycosaminoglycans, proteins, amides, and DNA. It was shown that during DET and BIO decellularization, composition aberrations of proteins and lipids do not occur and the integrity of the collagenous structures is preserved. It was found that during the DET decellularization, preservation of glycosaminoglycans is better than during BIO decellularization. [ABSTRACT FROM AUTHOR]

A stationary phase method and ambiguity function (AF) method were used to conduct an analytical study of a modulation transfer function (MTF). From the perspective of mathematic models, there was a double integral relationship between the MTF and system wave aberrations. Based on the stationary phase and AF methods, the wave aberration term in the MTF expression was analytically discussed to achieve an aberration function derivation and extreme point analysis, thereby obtaining the analytical expressions of an every field-ofview (FOV) MTF and defocusing distance (i.e., the deviation of an MTF optimal imaging plane from an axial imaging plane) in the full FOV of an optical system. From the obtained image quality evaluation function, the defocusing distance and system image quality could be effectively controlled in a full FOV, which was verified using the examples. [ABSTRACT FROM AUTHOR]

Optical aberrations significantly affect the resolution and signal-to-noise ratio of deep tissue microscopy. As multiphoton microscopy is applied deeper into tissue, the loss of resolution and signal due to propagation of light in a medium with heterogeneous refractive index becomes more serious. Efforts in imaging through the intact skull of mice cannot typically reach past the bone marrow (~150 µm of depth) and have limited resolution and penetration depth. Mechanical bone thinning or optical ablation of bone enables deeper imaging, but these methods are highly invasive and may impact tissue biology. Adaptive optics is a promising noninvasive alternative for restoring optical resolution. We characterize the aberrations present in bone using second- harmonic generation imaging of collagen. We simulate light propagation through highly scattering bone and evaluate the effect of aberrations on the point spread function. We then calculate the wavefront and expand it in Zernike orthogonal polynomials to determine the strength of different optical aberrations. We further compare the corrected wavefront and the residual wavefront error, and suggest a correction element with high number of elements or multiconjugate wavefront correction for this highly scattering environment. [ABSTRACT FROM AUTHOR]

I present the results of an optical design study into the performance benefits of non-rotationally symmetric "freeform" gradient-index (GRIN) media on a pupil-relay head-mounted display. A range of design variants are presented based on freeform-GRIN lenses consisting of ternary base-material combinations that are enabled by recent developments in additive manufacture. The optical performance of these designs is compared to homogeneous solutions comprising combinations of spherical, aspheric, toric, and freeform surfaces. I show that freeform-GRIN media represent powerful degrees of freedom for aberration correction in tilted and off-axis optical systems, performing comparably to homogeneous freeform optics while illustrating significant potential reductions in lens count and mass. [ABSTRACT FROM AUTHOR]

An approach for wavelength characterization whereby dynamic Fresnel zone plate (FZP) patterns are written to a digital micromirror device (DMD) and used to focus incoming light onto a camera is proposed. The incoming wavelength is then assessed by scanning the focal length. Rectangular basis Zernike modes are implemented to match the rectangular geometry of the DMD, we believe for the first time. A procedure is developed to correct for inherent aberrations of the optical system by adjusting the Zernike mode amplitudes, thus improving focal spot quality. The aberration corrected FZPs are used to assess the focusing conditions needed for four lasers of different visible wavelengths ranging from blue (405 nm) to near infrared (760 nm). The system is able to produce focused beams with a width of twice the diffraction limit and achieve a wavelength resolution of 3 nm. The operational wavelength of the system is ultimately limited by the spectral bandwidth of the detector. [ABSTRACT FROM AUTHOR]

Fourier ptychographic microscopy (FPM) enables quantitative phase imaging with a large field-of-view and high resolution by acquiring a series of low-resolution intensity images corresponding to different spatial frequencies stitched together in the Fourier domain. However, the presence of various aberrations in an imaging system can significantly degrade the quality of reconstruction results. The imaging performance and efficiency of the existing embedded optical pupil function recovery (EPRY-FPM) aberration correction algorithm are low due to the optimization strategy. An aberration correction method (AA-P algorithm) based on an improved phase recovery strategy is proposed to improve the reconstruction image quality. This algorithm uses adaptive modulation factors, which are added while updating iterations to optimize the spectral function and optical pupil function updates of the samples, respectively. The effectiveness of the proposed algorithm is verified through simulations and experiments using an open-source biological sample dataset. Experimental results show that the proposed AA-P algorithm in an optical system with hybrid aberrations, recovered complex amplitude images with clearer contours and higher phase contrast. The image reconstruction quality was improved by 82.6% when compared with the EPRY-FPM algorithm. The proposed AA-P algorithm can reconstruct better results with faster convergence, and the recovered optical pupil function can better characterize the aberration of the imaging system. Thus, our method is expected to reduce the strict requirements of wavefront aberration for the current FPM. [ABSTRACT FROM AUTHOR]

Focus-tunable lenses, e.g., liquid filled membrane lenses (MLs), have found increasingly widespread application in optical systems. If a large refractive power range is to be used, the correction of chromatic aberrations is particularly challenging: a group containing a single ML cannot be corrected over the whole refractive power range. In analogy to hybrid achromats for lenses with constant focal lengths, we present the combination of an ML and a diffractive Alvarez-Lohmann-lens (ALL) for the compensation of axial color over a large refractive power range. In contrast to the combination of multiple MLs, this does not increase the axial length of the system significantly. At the same time, the flexible adaption of the phase function of the diffractive ALL can reduce spherical aberration over the whole focal range. Design examples with ray-tracing and wave-optical simulations demonstrate the performance of the resulting hybrid tunable element. Experimental data from fabricated sample lenses provide a proof of principle. [ABSTRACT FROM AUTHOR]

To realize the quasi-quantitative Schlieren measurement of the shock train structure across the cylindrical isolator in the supersonic flow field, based on the theory of Schlieren measurement and light transmission, we propose the design scheme of conformal windows and discuss the machining feasibility with the window's parameters. The relationship between the Schlieren imaging effect, the deflection of parallel light in the Schlieren apparatus, and the conformal optical window aberrations was researched, putting forward the optical simulation model of the conformal optical windows and the quasi-quantitative Schlieren measurement. Moreover, considering the actual wind tunnel test conditions, under the speed of Mach 2 at the isolator's inlet, the distortion brought by conformal optical windows in the Schlieren observation region was simulated by the computational fluid dynamics method. Finally, the image correction algorithm for the distorted picture caused by the conformal windows was presented, and the quasi-quantitative Schlieren measurement through the conformal optical window pair was conducted for the experimental verification. The results reveal the quasi-quantitative Schlieren measurement effect across the high-precision conformal optical window pair of the cylindrical isolator, providing guidance on maintaining the balance between the manufacturing feasibility and the observation performance of conformal windows. [ABSTRACT FROM AUTHOR]

Freeform imaging systems are a subject of current interest. To aid in the design of such systems, we introduce structural aberration coefficients for plane symmetric imaging with XY-polynomial freeform surfaces that may also be tilted. Further, we extend the coefficients to systems with an arbitrary number of components and specifically provide analytical equations for two-mirror systems. Distinguishing between system configuration and structural parameters enhances clarity, which we highlight by deriving new conditions for minimum root-mean-square (RMS) spot size and minimum RMS wavefront error in aplanatic two-mirror telescopes. [ABSTRACT FROM AUTHOR]

An optical coherence tomography (OCT) system with a 2.8-mm beam diameter is presented. Sensorless defocus correction can be performed with a Badal optometer and astigmatism correction with a liquid crystal device. OCT B-scans were used in an image-based optimization algorithm for aberration correction. Defocus can be corrected from -4.3 D to þ4.3 D and vertical and oblique astigmatism from -2.5 D to þ2.5 D. A contrast gain of 6.9 times was measured after aberration correction. In comparison with a 1.3-mm beam diameter OCT system, this concept achieved a 3.7-dB gain in dynamic range on a model retina. Both systems were used to image the retina of a human subject. As the correction of the liquid crystal device can take more than 60 s, the subject's spectacle prescription was adopted instead. This resulted in a 2.5 times smaller speckle size compared with the standard OCT system. The liquid crystal device for astigmatism correction does not need a high-voltage amplifier and can be operated at 5 V. The correction device is small (9 mm × 30 mm × 38 mm) and can easily be implemented in existing designs for OCT. [ABSTRACT FROM AUTHOR]

The concept of the aberration function is extended to define two functions that describe the light irradiance distribution at the exit pupil plane and at the image plane of an axially symmetric optical system. Similar to the wavefront aberration function, the irradiance function is expanded as a polynomial, where individual terms represent basic irradiance distribution patterns. Conservation of flux in optical imaging systems is used to derive the specific relation between the irradiance coefficients and wavefront aberration coefficients. It is shown that the coefficients of the irradiance functions can be expressed in terms of wavefront aberration coefficients and firstorder system quantities. The theoretical results--these are irradiance coefficient formulas--are in agreement with real ray tracing. [ABSTRACT FROM AUTHOR]

We describe the principles of using orientation-independent differential interference contrast (OI-DIC) microscopy for mapping optical path length (OPL). Computation of the scalar two-dimensional OPL map is based on an experimentally received map of the OPL gradient vector field. Two methods of contrast enhancement for the OPL image, which reveal hardly visible structures and organelles, are presented. The results obtained can be used for reconstruction of a volume image. We have confirmed that a standard research grade light microscope equipped with the OI-DIC and 100×/1.3 NA objective lens, which was not specially selected for minimum wavefront and polarization aberrations, provides OPL noise level of ~0.5 nm and lateral resolution if ~300 nm at a wavelength of 546 nm. The new technology is the next step in the development of the DIC microscopy. It can replace standard DIC prisms on existing commercial microscope systems without modification. This will allow biological researchers that already have microscopy setups to expand the performance of their systems. [ABSTRACT FROM AUTHOR]

We theoretically represent the effectiveness of the odd-order surface for optical designs via an aberration theory. The theory employs an expression of the odd-order surface with aberration coefficients, which are derived by power-series expansion of wavefront aberration with respect to the coordinates of optical surfaces. This expression allows us to understand the aberration characteristics of odd-order surfaces. By applying this aberration theory to the design of extreme ultraviolet lithography optics, we show that odd-order surfaces are effective in reducing higher-order aberrations with fewer coefficients than even-order surfaces do. [ABSTRACT FROM AUTHOR]

The accuracy of the Shack-Hartmann wavefront sensor for measuring wavefront aberrations is mainly dependent upon the measuring accuracy of the centroid of each spot. An effect of the aperture of the 4F system on the correlation properties of speckle patterns produced with monochromatic light is investigated at the Shack-Hartmann sensor plane and at the focal plane of the sensor. An expression for a speckle patterns correlation length changing due to the extended aperture of the 4F system is derived by Fourier optics method. The experimental results that confirm the theoretical dependence quality within the limits of errors are obtained, and it is shown that the spatial finiteness of the optical system causes significant changes of transferred aberrated field. [ABSTRACT FROM AUTHOR]

Optical aberrations due to refractive index mismatches occur in various types of microscopy due to refractive differences between the sample and the immersion fluid or within the sample. We study the effects of lateral refractive index differences by fluorescence confocal laser scanning microscopy due to glass or polydimethylsiloxane cuboids and glass cylinders immersed in aqueous fluorescent solution, thereby mimicking realistic imaging situations in the proximity of these materials. The reduction in fluorescence intensity near the embedded objects was found to depend on the geometry and the refractive index difference between the object and the surrounding solution. The observed fluorescence intensity gradients do not reflect the fluorophore concentration in the solution. It is suggested to apply a Gaussian fit or smoothing to the observed fluorescence intensity gradient and use this as a basis to recover the fluorophore concentration in the proximity of the refractive index step change. The method requires that the reference and sample objects have the same geometry and refractive index. The best results were obtained when the sample objects were also used for reference since small differences such as uneven surfaces will result in a different extent of aberration. [ABSTRACT FROM AUTHOR]

Active optics such as deformable mirrors can be used to control both focal depth and aberrations during scanning laser microscopy. If the focal depth can be changed dynamically during scanning, then imaging of oblique surfaces becomes possible. If aberrations can be corrected dynamically during scanning, an image can be optimized throughout the field of view. Here, we characterize the speed and dynamic precision of a Boston Micromachines Corporation Multi-DM 140 element aberration correction mirror and a Revibro Optics 4-zone focus control mirror to assess suitability for use in an active and adaptive two-photon microscope. Tests for the multi-DM include both step response and sinusoidal frequency sweeps of specific Zernike modes (defocus, spherical aberration, coma, astigmatism, and trefoil). We find wavefront error settling times for mode amplitude steps as large as 400 nm to be less than 52 μs, with 3 dB frequencies ranging from 6.5 to 10 kHz. The Revibro Optics mirror was tested for step response only, with wavefront error settling time less than 80 μs for defocus steps up to 3000 nm, and less than 45 μs for spherical aberration steps up to 600 nm. These response speeds are sufficient for intrascan correction at scan rates typical of two-photon microscopy. [ABSTRACT FROM AUTHOR]

We describe a simple and compact full-field optical coherence tomography (FFOCT) setup coupled to a transmissive liquid crystal spatial light modulator (LCSLM) to induce or correct aberrations. To reduce the system complexity, strict pupil conjugation was abandoned because low-order aberrations are often dominant. We experimentally confirmed a recent theoretical and experimental demonstration that the image resolution was almost insensitive to aberrations that mostly induce a reduction of the signal level. As a consequence, an imagebased algorithm was applied for the optimization process by using the FFOCT image intensity as the metric. Aberration corrections were demonstrated with both an USAF resolution target and biological samples for LCSLM-induced and sample-induced wavefront distortions. [ABSTRACT FROM AUTHOR]

Our ability to see fine detail at depth in tissues is limited by scattering and other refractive characteristics of the tissue. For fixed tissue, we can limit scattering with a variety of clearing protocols. This allows us to see deeper but not necessarily clearer. Refractive aberrations caused by the bulk index of refraction of the tissue and its variations continue to limit our ability to see fine detail. Refractive aberrations are made up of spherical and other Zernike modes, which can be significant at depth. Spherical aberration that is common across the imaging field can be corrected using an objective correcting collar, although this can require manual intervention. Other aberrations may vary across the imaging field and can only be effectively corrected using adaptive optics. Adaptive optics can also correct other aberrations simultaneously with the spherical aberration, eliminating manual intervention and speeding imaging. We use an adaptive optics two-photon microscope to examine the impact of the spherical and higher order aberrations on imaging and contrast the effect of compensating only for spherical aberration against compensating for the first 22 Zernike aberrations in two tissue types. Increase in image intensity by 1.6× and reduction of root mean square error by 3× are demonstrated. [ABSTRACT FROM AUTHOR]

We describe a wavefront sensor strategy for the implementation of adaptive optics (AO) in microscope applications involving thick, scattering media. The strategy is based on the exploitation of multiple scattering to provide oblique back illumination of the wavefront-sensor focal plane, enabling a simple and direct measurement of the flux-density tilt angles caused by aberrations at this plane. Advantages of the sensor are that it provides a large measurement field of view (FOV) while requiring no guide star, making it particularly adapted to a type of AO called conjugate AO, which provides a large correction FOV in cases when sample-induced aberrations arise from a single dominant plane (e.g., the sample surface). We apply conjugate AO here to widefield (i.e., nonscanning) fluorescence microscopy for the first time and demonstrate dynamic wavefront correction in a closed-loop implementation. [ABSTRACT FROM AUTHOR]

Several factors impact the light irradiance and relative illumination produced by a lens system at its image plane. In addition to cosine-fourth-power radiometric law, image and pupil aberrations and light vignetting also count. We use an irradiance transport equation to derive a closed form solution that provides insight into how individual aberration terms affect the light irradiance and relative illumination. The theoretical results are in agreement with real ray tracing. [ABSTRACT FROM AUTHOR]

Objective measurement of straylight in the human eye with a Shack-Hartmann (SH) wavefront aberrometer is limited in imaging angle. We propose a measurement principle and a point spread function (PSF) reconstruction algorithm to overcome this limitation. In our optical setup, a variable stop replaces the stop conventionally used to suppress reflections and scatter in SH aberrometers. We record images with 21 diameters of the stop. From each SH image, the average intensity of the pupil is computed and normalized. The intensities represent integral values of the PSF. We reconstruct the PSF, which is the derivative of the intensities with respect to the visual angle. A modified Stiles Holladay approximation is fitted to the reconstructed PSF, resulting in a straylight parameter. A proof-of-principle study was carried out on eight healthy young volunteers. Scatter filters were positioned in front of the volunteers' eyes to simulate straylight. The straylight parameter was compared to the C-Quant measurements and the filter values. The PSF parameter shows strong correlation with the density of the filters and a linear relation to the C-Quant straylight parameter. Our measurement and reconstruction techniques allow for objective straylight analysis of visual angles up to 4 deg. [ABSTRACT FROM AUTHOR]

The goal of this work was to objectively characterize the external morphology, topography, and optics of the cornea after orthokeratology (ortho-k). A number of 24 patients between the ages of 17 and 30 years (median = 24 years) were fitted with Corneal Refractive Therapy® contact lenses to correct myopia between -2.00 and -5.00 diopters (D) (median = -3.41 D). A classification algorithm was applied to conduct an automatic segmentation based on the mean local curvature. As a result, three zones (optical zone, transition zone, and peripheral zone) were delimited. Topographical analysis was provided through global and zonal fit to a general ellipsoid. Ray trace on partially customized eye models provided wave aberrations and retinal image quality. Monozone topographic description of the ortho-k cornea loses accuracy when compared with zonal description. Primary (C04 ) and secondary (C06 ) spherical aberration (SA) coefficients for a 5-mm pupil increased 3.68 and 19 times, respectively, after the treatments. The OZ area showed a strong correlation with C04 (r = -0.49, p < 0.05) and a very strong correlation with C06 (r = 0.78, p < 0.01). The OZ, as well as the TZ, areas did not correlate with baseline refraction. The increase in the eye's positive SA after ortho-k is the major factor responsible for the decreased retinal optical quality of the unaccommodated eye. [ABSTRACT FROM AUTHOR]

The mask plays a significant role as an active optical element in lithography, for both deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography. Mask-induced and feature-dependent shifts of the best-focus position and other aberration-like effects were reported both for DUV immersion and for EUV lithography. We employ rigorous computation of light diffraction from lithographic masks in combination with aerial image simulation to study the root causes of these effects and their dependencies from mask and optical system parameters. Special emphasis is put on the comparison of transmission masks for DUV lithography and reflective masks for EUV lithography, respectively. Several strategies to compensate the mask-induced phase effects are discussed. [ABSTRACT FROM AUTHOR]

The eigenmode of resonators with symmetric circular mirrors used in solid-state lasers is investigated. Further experiments on output beam quality on a passive Q-switched zigzag slab Nd:YAG laser have been performed by adopting Hartmann-Shack and Zernike-mode reconstruction methods. By the means of peakvalley and root mean square errors of the wavefront distribution, each order of Zernike aberrations are achieved accurately. Moreover, the distribution of circle energy in the far-field and corresponding beam evaluation factors can also be obtained by further calculation. Experimental results indicate that the wavefront aberration is mainly concentrated in the first 10 Zernike aberrations, which mainly includes the defocus Z3, the low-order astigmatism Z5, the coma aberration Z6, and the spherical aberration Z10, because of the crystal thermal effect and the intracavity phase perturbation. The method can be used to further analyze the compensation of intracavity aberration and optimal design for such lasers. [ABSTRACT FROM AUTHOR]

A modified low-cost unimorph deformable mirror (DM) driven only by positive voltages for atmospheric turbulence compensation is presented. The 214 patterned inner actuators generate convex deformations for aberration correction, while one outer ring actuator generates an overall concave bias. To evaluate the aberration correction capability of the proposed DM, the iterative reconstruction of Zernike aberrations and correction were performed in an adaptive optics test system. The experimental results indicate that the fabricated DM has an excellent aberration correction capability, particularly matching the first 20 term Zernike aberrations with the normalized residual root-mean-square (RMS) error <5%. Furthermore, the random atmospheric turbulence aberrations were simulated based on Karhunen-Loève coefficients and reconstructed using the fabricated DM. The simulative and experimental results show that the atmospheric turbulence aberrations can be steadily compensated with λ/40 (λ = 2.2 µm) RMS residual error, indicating the prospect for atmospheric applications. [ABSTRACT FROM AUTHOR]

The influence of various types of aberrations (spherical, coma, and astigmatic) of recording and readout beams on the readout signal in a microholographic recording was investigated through a numerical simulation. The simulation conditions were that the wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. The tolerance of the root-mean-square (RMS) wavefront aberrations was defined as the aberration when the normalized signal level decreased to 0.8. Among the three types of aberrations, the influence of the spherical aberration was the most significant. When both the recording and readout beams were aberrated and the signs of the aberrations were in the worst case, the tolerance of the RMS wavefront aberrations was less than half of the Maréchal's criterion. Moreover, when the RMS wavefront aberrations of the recording and readout beams were within the above tolerance, the bit intervals of 0.13 and 0.65 µm in the inplane and vertical directions, respectively, which correspond to the recording density of 91 bit/µm³ (recording capacity of 16 TB for a 120-mm-diameter optical disk having a 300-µm-thick recording layer), were shown to be feasible for confocal detection with an allowable signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

The wavefront aberrations induced by misalignments due to decentration and tilt of an optical component in an optical measurement system are presented. A Shack-Hartmann wavefront sensor is used to measure various aberrations caused due to the shifting of the axis and tilt of a lens in the path of an optical wavefront. One of the lenses in an optical system is decentered in the transverse direction and is tilted by using a rotational stage. For each step, wavefront data have been taken and data were analyzed up to the fourth order consisting of 14 Zernike terms along with peak-to-valley and root mean square values. Theoretical simulations using ray tracing have been carried out and compared with experimental values. The results are presented along with the discussion on tolerance limits for both decentration and tilt. [ABSTRACT FROM AUTHOR]

To better understand how the eye's optics affects stereopsis, we measured stereoacuity before and after higher-order aberration (HOA) correction with a binocular adaptive optics visual simulator. The HOAs were corrected either binocularly or monocularly in the better eye (the eye with better contrast sensitivity). A two-line stereo pattern served as the visual stimulus. Stereo thresholds at different viewing durations were obtained with the psychophysical method of constant stimuli. Binocular HOA correction led to significant improvement in stereoacuity. However, better eye HOA correction could bring either a bad degradation or a slight improvement in stereoacuity. As viewing duration increased, the stereo benefit approached the level of 1.0 for both binocular and better eye correction, suggesting that long viewing durations might weaken the effects of the eye's optical quality on stereopsis. [ABSTRACT FROM AUTHOR]

A three-dimensional (3-D) point spread function (PSF) model for wide-field fluorescence microscopy, suitable for imaging samples with variable refractive index (RI) in multilayered media, is presented. This PSF model is a key component for accurate 3-D image restoration of thick biological samples, such as lung tissue. Microscope- and specimen-derived parameters are combined with a rigorous vectorial formulation to obtain a new PSF model that accounts for additional aberrations due to specimen RI variability. Experimental evaluation and verification of the PSF model was accomplished using images from 175-nm fluorescent beads in a controlled test sample. Fundamental experimental validation of the advantage of using improved PSFs in depth-variant restoration was accomplished by restoring experimental data from beads (6 µm in diameter) mounted in a sample with RI variation. In the investigated study, improvement in restoration accuracy in the range of 18 to 35% was observed when PSFs from the proposed model were used over restoration using PSFs from an existing model. The new PSF model was further validated by showing that its prediction compares to an experimental PSF (determined from 175-nm beads located below a thick rat lung slice) with a 42% improved accuracy over the current PSF model prediction. [ABSTRACT FROM AUTHOR]

Figure errors of optical surfaces degrade the performance of optical systems. When predicting the performance and performing system assembly, compensation by clocking of optical components around the optical axis is a conventional but user-dependent method. Commercial optical software cannot optimize this clocking, and existing automatic figure-error balancing methods have limitations. To overcome these limitations, a global and general optimization method based on analyzing the precise relationships between the figure errors and the wavefront error (WFE) is proposed. Using the footprint data of each optical surface, the resulting WFE is calculated. Direct map operation is used for intercepting and rotating the figure-error maps. The simulated annealing algorithm is used to seek the optimal combination of clocking angles for the optical components. This method can be applied to most coaxial optics systems, including dioptric, catoptrics, and catadioptric complex lenses. It is successfully implemented for a catadioptric immersion lithographic optics system with artificial figure errors, and for an experimental lithographic optics system with actual manufacturing figure errors. [ABSTRACT FROM AUTHOR]

We first investigated the similarity in optical quality of a batch of diffractive intraocular lenses (DIOLs), providing experimental evidence for one DIOL as representative of a batch. Using adaptive optics, we then evaluated one DIOL under different levels of Zernike spherical aberration (SA) by applying both a point spread function test and a psychophysical visual acuity test. We found that for small aperture size SA has the effect of shifting the through-focus curve of DIOL. Also, for a relatively large aperture size, it has different effects on the distant and near foci. [ABSTRACT FROM AUTHOR]

Spatial frequency domain imaging (SFDI) and spatial frequency domain spectroscopy (SFDS) are emerging tools to non-invasively assess tissues. However, the presence of aberrations can complicate processing and interpretation. This study develops a method to characterize optical aberrations when performing SFDI/S measurements. Additionally, we propose a post-processing method to compensate for these aberrations and recover arbitrary subsurface optical properties. Using a custom SFDS system, we extract absorption and scattering coefficients from a reference phantom at 0 to 15 mm distances from the ideal focus. In post-processing, we characterize aberrations in terms of errors in absorption and scattering relative to the expected in-focus values. We subsequently evaluate a compensation approach in multi-distance measurements of phantoms with different optical properties and in multi-layer phantom constructs to mimic subsurface targets. Characterizing depth-specific aberrations revealed a strong power law such as wavelength dependence from ∼40 to ∼10 % error in both scattering and absorption. When applying the compensation method, scattering remained within 1.3% (root-mean-square) of the ideal values, independent of depth or top layer thickness, and absorption remained within 3.8%. We have developed a protocol that allows for instrument-specific characterization and compensation for the effects of defocus and chromatic aberrations on spatial frequency domain measurements. [ABSTRACT FROM AUTHOR]

Wavefront aberration is an essential factor that significantly affects the image quality of an optical system. We proposed a comprehensive method to determine the wavefront aberration of a deformed optical component caused by clamping forces. First, the displacement of the elements on the optical component, induced by external forces, is calculated using ANSYS software. Then, the deformation surface is fitted with an aspherical surface to obtain Zernike coefficients. Finally, the wavefront aberration is obtained from Zemax using the Zernike coefficients and the parameters of the optical component. An experimental study on a spherical mirror is carried out to verify the accuracy of this method. A Zygo interferometer is used to measure the actual wavefront aberration of the deformed mirror. The result indicates a good agreement between the theoretical calculation and the experimental data, with a variation of <10 % for various applied forces. Our finding provides a meaningful and reliable method for designing and selecting reasonable mounting structures to ensure the image quality of an optical system. [ABSTRACT FROM AUTHOR]

Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces. An off-axis two-mirror-based telescope design is presented, in which the primary mirror is a concave prolate spheroid and the secondary mirror is freeform surface-based. The off-axis configuration is employed here for removing the central obscuration problem which otherwise limits the central maxima in the point spread function. In this proposed design, an extended X - Y polynomial is used as a surface descriptor for the off-axis segment of the secondary mirror. The coefficients of this extended polynomial are directly related to the Seidel aberrations, and are thus optimized here for a better control of asymmetric optical aberrations at various field points. For this design, the aperture stop is located 500 mm before the primary mirror and the entrance pupil diameter is kept as 80 mm. The effective focal length is 439 mm and covers a full field of view of 2 deg. The image quality obtained here is near diffraction limited which can be inferred from metrics such as the spot diagram and modulation transfer function. [ABSTRACT FROM AUTHOR]