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The amorphous calcogenide semiconductor As0.63S2.70Sb1.37Te0.30 was synthesized and thin films based on it were obtained. XRD and optical images investigations showed the amorphous and homogeneous nature of the samples. The optical transmission spectrum in the UV-Vis range of As0.63S2.70Sb1.37Te0.30 thin films shows good transparency in the spectral range 0.7-3.5 µm with a single absorption threshold at 2.05 eV and with refractive index in infrared 2.3. The irradiation of films with light leads to a parallel shift of the transmission spectrum to the IR range. The materials with As0.63S2.70Sb1.37Te0.30 composition have high optical transparency have high optical transparency that make they promises for applications in holographic memory devices, optical amplitude and phase recorder, optical processing units and others. [ABSTRACT FROM AUTHOR]

Benefitting from low propagation loss and complementary metal–oxide–semiconductor compatibility, Si 3 N 4 is heavily explored for the applications of nonlinear optical signal processing. However, the Si 3 N 4 waveguide is limited by its low optical Kerr nonlinearity. In this work, we introduce highly nonlinear ultra-Si-rich-nitride (USRN) deposited by the plasma enhanced chemical vapor deposition system. The measured linear refractive index of USRN is 3.09 at a wavelength of 1550 nm, while the Kerr nonlinearity of the USRN waveguide is experimentally extracted with a value of 2.25 × 10 − 17 m 2 /W. Moreover, a broadband wavelength conversion ranging from S-band to L-band by a four-wave-mixing experiment is realized via designed USRN waveguide with a relatively short length of 3 mm. The measured bandwidth is 190 nm with a continuous-wave pump laser located at 1530 nm. The conversion efficiency is measured approximately − 48 dB under a relatively low pump power of 7 dBm. [ABSTRACT FROM AUTHOR]

This paper describes a low-cost laboratory experiment designed to demonstrate the applicability of the refractive index to study stratification in fluids. The laser refractography method was applied to a linearly vertical density profile of a salt (NaCl) stratified water column. Next, an image processing procedure was performed, consisting of the binarization and edge detection of the laser beam and its subsequent second-order polynomial best fit. Quantitatively, the whole-field results compared well with the respective measured density profiles. This method allows one to obtain quantitative measurements of density profiles in stratified fluids with good accuracy, making it a suitable experimental method for laboratory demonstrations on fluids. [ABSTRACT FROM AUTHOR]

In the present manuscript, the characterisation was done on liquid crystalline n-hexyloxycyanobiphenyl (6ocb) compound with dispersed citrate-capped gold nanoparticles (Au NPs) at different concentrations. It is observed that the birefringence enhances with increase in concentration of Au NPs. Also, strong Vander Waal's interaction takes place due to well capping between the Au NPs and 6ocb molecules. The refractive indices are determined by using modified spectrometer at different wavelengths. The orientational order parameter has been determined from various theoretical molecular internal field models namely, Kuczynski, Effective geometry, Haller's extrapolation and Vuks. The dispersive power ω is estimated for two consecutive wavelengths for the case of , ne and no at different wavelengths found to be constant with temperature. The values of cross-over temperature, TCO determined from the temperature gradients of ne and no. Further, the refractive indices measured are fitted with two and three coefficient Cauchy model. Three coefficient Cauchy model is favourable than two coefficient Cauchy model for high birefringence liquid crystals. The results obtained are compared and discussed. Further, the phase transitions can be easily identified by GMSD Image processing method with Matlab tool to reduce the costly equipment's usage in finding the heat flow with respect to temperature. [ABSTRACT FROM AUTHOR]

By experimental measurements and theoretical analyses, this paper investigates the variation of the Sun's visual shape and figures out the reasons for the variation of its shape. First, the method of image processing, the method of moments and the least-square method are combined to perform experimental measurements and calculations, and the features of the Sun's visual shape are extracted from the photos of the Sun. Second, theoretical analyses are conducted based on atmospheric refraction and the Einstein's special relativity theory. The relationship model is established between the zenith and azimuth angles of the Sun, the velocity of the Sun relative to the Earth, and the observation time and position; the refraction index of the atmosphere is expressed as a function of altitude and wavelength of light; an iterative algorithm is constructed to trace rays of light in the atmosphere; a set of formulas is derived to determine the contraction ratio and contraction direction of the Sun's visual shape. Finally, the theoretical and experimental results are compared; their relative errors are less than 0.3%, which verifies the theoretical analyses. Both theoretically and experimentally, this research proves that the Sun's visual shape is an ellipse; its shape variation mainly results from atmospheric refraction effects; and the length contraction effect of the Einstein's special relativity also contributes a little, except at the time of sunrise and sunset. [ABSTRACT FROM AUTHOR]

In this paper, we report a series of incremental optical coding and decoding sensors using their respective fiber Bragg grating superstructure (SS-FBG). We performed a comparative study of the encoding/decoding bipolar and unipolar sequences using these grids. The modulation in the refractive index can be changed by discrete jumps in phase (± π) or variations in the amplitude of the specific grid regions. The aim of this study was to evaluate the performance of SS-FBG in autocorrelation and cross-correlation studies. This approach allows us to measure the quality of unipolar and bipolar coding and understand how the decoded signal can be affected by the presence of multiple users on the network. Each generated code is a Gold sequence for bipolar code 63chips and an M sequence for unipolar code 63chips. We use five different codes to represent the users, and we calculate through the signal/noise power ratio (SRNe) the energy used by a certain signal to interfere with a neighboring signal. Our results emphasize the accuracy and flexibility of Bragg gratings (FBG-SS) and showed that this technology is promising not only to Optical Code Division Multiple Access (OCDMA) but also for an extended variety of other optical processing applications. [ABSTRACT FROM AUTHOR]

The index of refraction (n) of materials and/or tissues depends on their physical properties and serves as a source of optical contrast in imaging. The variations of the index of refraction have also been investigated for diagnostic purposes in various fields, such as hematology, oncology, etc., since they can signify disease and cell dynamic changes. Optical coherence tomography (OCT) has been used in the past to measure the index ex vivo. However, most methodologies described in the literature are not appropriate for in vivo imaging since they require either a mirror below the sample or a complicated imaging setup and algorithms. We describe a technique that uses two images, obtained at different angles, to estimate the index of refraction and can, thus, also be applied in vivo. The index of refraction is calculated from the path-length difference observed by the OCT beam at the two different angles. When a reflector is not available, the path-length difference can be estimated using image registration and the cross-correlation of adjacent A-scans. The proposed technique was validated experimentally using both clear and scattering samples. The resulting values of the index of refraction were within ~1% of the expected. The main limitation of this technique is the effect of misalignment on the results, requiring the precision provided by an angular-resolved OCT system. These very promising results provide evidence that the dual-angle method should be further investigated and validated on human tissues so that it can be developed into a clinically useful diagnostic tool in the future. [ABSTRACT FROM AUTHOR]

Background Oriented Schlieren (BOS) is a non-intrusive optical method used to visualize density variations in fluids. A camera is used to measure the distortion of a background image displaying a random pattern due to the refraction of the light induced by the local gradients in the refractive index of the under study. In contrast to conventional schlieren, for which direct observation is possible, the images obtained with the BOS technique have to be processed. In this contribution, a computationally affordable approach based on linear least-squares minimization and adapted from optical flow techniques is presented in detail and tested in the context of BOS with the Matlab GUI application comBOS. A series of synthetic images are first analyzed to devise design rules for the definition of an optimal random Gaussian dot background pattern. Tests are performed for comBOS, the commercial BOS module included in DaVis 10, and the free PIV tool PIVlab. It is found that the diameter of the dot images on the camera sensor should be at least 3 pixels, but can be larger without affecting the accuracy of the measurement with comBOS and DaVis 10, while PIVlab severely degrades the quality of the results for dots larger than 5 pixels. The contrast and the density of dots must also be sufficient such that a minimum of 75 % of the surface of the background is shaded. If these conditions are met, the maximum systematic error in the measured distortions is 0.006 pixel for comBOS and 0.001 pixel with DaVis 10 when local gradients are small. Similar errors are found with PIVlab for dots smaller than 5 pixels in diameter, but they increase rapidly for larger dots. The random error is typically smaller than 0.004 pixel in optimal conditions, but it increases significantly for images affected by a random noise or local gradients of the distortion. Finally, it is concluded with a realistic test case that both comBOS and DaVis 10 are well suited to capture the main features of a complex compressible flow with Schlieren imaging. Thus, the main advantage of comBOS is its affordability and robustness for researchers and educators willing to implement BOS, for example in educational contexts. • A BOS Image Processing algorithm that is used in the application comBOS is presented. • Unlike common tools, linear least squares fitting is used instead of correlation. • Design rules are devised to build an optimal background for comBOS and DaVis 10. • Performances are found similar between comBOS and the BOS module of DaVis 10. [ABSTRACT FROM AUTHOR]

A single‐image method is proposed for quantitative phase retrieval in hard X‐ray grating interferometry. This novel method assumes a quasi‐homogeneous sample, with a constant ratio between the real and imaginary parts of its complex refractive index. The method is first theoretically derived and presented, and then validated by synchrotron radiation experiments. Compared with the phase‐stepping method, the presented approach abandons grating scanning and multiple image acquisition, and is therefore advantageous in terms of its simplified acquisition procedure and reduced data‐collection times, which are especially important for applications such as in vivo imaging and phase tomography. Moreover, the sample's phase image, instead of its first derivative, is directly retrieved. In particular, the stripe artifacts encountered in the integrated phase images are significantly suppressed. The improved quality of the retrieved phase images can be beneficial for image interpretation and subsequent processing. Owing to its requirement for a single image and its robustness against noise, the present method is expected to find use in potential investigations in diverse applications. A single‐image method is proposed for quantitative phase retrieval in hard X‐ray grating interferometry. This method assumes a quasi‐homogeneous sample, with a constant ratio between the real and imaginary parts of its complex refractive index. Experimental synchrotron radiation results demonstrate that the method can provide phase images of improved quality and is highly stable against noise. [ABSTRACT FROM AUTHOR]

A method of measuring the refractive index of a particle is presented from a glare-point image. The space of a doublet image of a particle can be determined with high accuracy by using auto-correlation and Gaussian interpolation, and then the refractive index is obtained from glare-point separation, and a factor that may influence the accuracy of glare-point separation is explored. Experiments are carried out for three different kinds of particles, including polystyrene latex particles, glass beads, and water droplets, whose measuring accuracy is improved by the data fitting method. The research results show that the method presented in this paper is feasible and beneficial to applications such as spray and atmospheric composition measurements. [ABSTRACT FROM AUTHOR]

The refractive index is a fundamental physical property of a medium, which can be used for the identification and purity issues of all media. Here we describe a refractive index measurement technique to determine simultaneously the refractive index of different solid particles by monitoring the transmittance of light from a suspension using a charge-coupled device (CCD) camera. An important feature of the measurement is the liquid evaporation process for the refractive index matching of the solid particle and the immersion liquid; this was realized by using a pair of volatile and non-volatile immersion liquids. In this study, refractive indices of calcium fluoride (CaF2) and barium fluoride (BaF2) were determined using the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: Light field near eye displays (LFNED) can produce lightweight devices and address the accommodation–convergence conflict. However, low spatial resolution creates a poor immersive experience in LFNED. In addition, although many e‐shifting devices have been proposed to enhance resolution in projection system, yet those devices are too bulky to be applied in an LFNED to keep it lightweight. In this paper, a compact e‐shifting component is proposed to enhance image resolution in an LFNED by using a birefringent plate and twisted nematic switch cell. The proposed e‐shifting device is a flat and thin component with only 2.6 mm of thickness, which could be placed in the gap of an LFNED without increasing the thickness. The results show that the proposed components could be easily integrated in an LFNED with the result of resolution enhancement. [ABSTRACT FROM AUTHOR]

In this paper we propose a method to convert the local variations of refractive index into local changes of one surface of the lens, which then can then be described as a free-form surface, easy to introduce in conventional simulation tools. The proposed method tries to provide an equivalent model of the lens with refractive index variations where the index changes have been replaced for local thickness variations on the len's surface. The local thickness variations can be fitted at a freeform description that holds all the local index variations through the OPD (Optical patch difference) using a B-Spline description and a simplex algorithm to find the best fitted surface. [ABSTRACT FROM AUTHOR]

Ghost imaging with a fully spatially incoherent source in transparent liquid is investigated theoretically and numerically. The effects of water depth, refractive index of media and object position on noise property of ghost imaging in transparent liquid are studied by using classical optical theory. Based on simulation results, we find that for different media, ghost imaging with high quality can be obtained by selecting appropriate water depth and object position which may be helpful for underwater ghost imaging. [ABSTRACT FROM AUTHOR]

A new method for extracting the dots is proposed by the reflected light image of porous silicon (PSi) microarray utilization in this paper. The method consists of three parts: pretreatment, tilt correction and spot segmentation. First, based on the characteristics of different components in HSV (Hue, Saturation, Value) space, a special pretreatment is proposed for the reflected light image to obtain the contour edges of the array cells in the image. Second, through the geometric relationship of the target object between the initial external rectangle and the minimum bounding rectangle (MBR), a new tilt correction algorithm based on the MBR is proposed to adjust the image. Third, based on the specific requirements of the reflected light image segmentation, the array cells are segmented into dots as large as possible and the distance between the dots is equal in the corrected image. Experimental results show that the pretreatment part of this method can effectively avoid the influence of complex background and complete the binarization processing of the image. The tilt correction algorithm has a shorter computation time, which makes it highly suitable for tilt correction of reflected light images. The segmentation algorithm makes the dots in a regular arrangement, excludes the edges and the bright spots. This method could be utilized in the fast, accurate and automatic dots extraction of the PSi microarray reflected light image. [ABSTRACT FROM AUTHOR]

We have investigated the influence of an image charge effect (ICE) on the energies of the ground and first few excited states of a hydrogen-like impurity in a spherical quantum dot (QD) in the presence of an external electric field. The oscillator strengths of transitions from the 1 s -like state to excited states of 2 p x and 2 p z symmetries are calculated as the functions of the strengths of the confinement potential and the electric field. Also, we have studied the effect of image charges on linear and third-order nonlinear optical absorption coefficients and refractive index changes (RICs). The results show that image charges lead to the decrease of energies for all the hydrogen-like states, to the significant enhancement of the oscillator strengths of transitions between the impurity states, and to comparatively large blue shifts in linear, nonlinear, and total absorption coefficients and refractive index changes. Our results indicate that the total optical characteristics can be controlled by the strength of the confinement and the electric field. [ABSTRACT FROM AUTHOR]

In the presented work we aimed at improving confocal imaging to obtain highest possible resolution in thick biological samples, such as the mouse oocyte. We therefore developed an image processing workflow that allows improving the lateral and axial resolution of a standard confocal microscope. Our workflow comprises refractive index matching, the optimization of microscope hardware parameters and image restoration by deconvolution. We compare two different deconvolution algorithms, evaluate the necessity of denoising and establish the optimal image restoration procedure. We validate our workflow by imaging sub resolution fluorescent beads and measuring the maximum lateral and axial resolution of the confocal system. Subsequently, we apply the parameters to the imaging and data restoration of fluorescently labelled meiotic spindles of mouse oocytes. We measure a resolution increase of approximately 2-fold in the lateral and 3-fold in the axial direction throughout a depth of 60 μm. This demonstrates that with our optimized workflow we reach a resolution that is comparable to 3D-SIM-imaging, but with better depth penetration for confocal images of beads and the biological sample. [ABSTRACT FROM AUTHOR]

A maximum-likelihood reconstruction technique for X-ray Talbot-Lau tomography is presented. This technique allows the iterative simultaneous reconstruction of discrete distributions of absorption coefficient, refractive index and a dark-field scattering coefficient. This technique avoids prior phase retrieval in the tomographic projection images and thus in principle allows reconstruction from tomographic data with less than three phase steps per projection. A numerical phantom is defined which is used to evaluate convergence of the technique with regard to photon statistics and with regard to the number of projection angles and phase steps used. It is shown that the use of a random phase sampling pattern allows the reconstruction even for the extreme case of only one single phase step per projection. The technique is successfully applied to measured tomographic data of a mouse. In future, this reconstruction technique might also be used to implement enhanced imaging models for X-ray Talbot-Lau tomography. These enhancements might be suited to correct for example beam hardening and dispersion artifacts and improve overall image quality of X-ray Talbot-Lau tomography. [ABSTRACT FROM AUTHOR]

In the current work, the authors present the systematic study on linear and nonlinear optical properties of Copper-phathalocyanine thin film deposited by thermal evaporation system for the first time. The thickness of the prepared thin film was measured and found to be ~300 nm. X-ray diffraction and AFM study confirms that the prepared thin film possess good quality. The orientation of the grown thin film is found to be along (100). UV–vis-NIR study shows that the deposited thin film is highly transparent (>80%) in the wavelength range of 700–2500 nm. Further, the recorded optical data was used to determine the various linear and nonlinear optical parameters. The calculated value of refractive index is found to be in the range of 0.4–1.0. The direct and indirect band gap value is found to be 2.9 and 3.25 eV, respectively. The value of linear and nonlinear susceptibilities is found to be in order of 10 −12 . The higher value of linear and nonlinear parameters makes it suitable for optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for viewing angle enhancement in a parallax barrier based one-dimensional (1D) integral imaging display system. The viewing angle in a parallax barrier integral imaging system is defined by the angle between the center of slit and exit ray from elemental image. In this regard, we employ a refractive index medium between the elemental image plane and parallax barrier. Thus, the use of a refractive index medium allows us to increase the angle of exit ray, and may result in a viewing angle enhancement of display system. To test the feasibility of the proposed method, experiments are carried out and the results are comparatively analyzed with the conventional method. Experimental results reveal that the proposed method outperforms the conventional method. [ABSTRACT FROM AUTHOR]

The isotropic - blue phases - cholesteric phase transitions are studied in a thermotropic (COC) by image processing and refractive index measurements. Textures of blue phases are optically characterized as well as their transition points. The experimental investigation employed here is sensitive to detect changes in the structural configuration of blue phases as a consequence of our refractive index data. In this context the experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

We report the experimental results of structural parameters measurement of the polarization-maintaining fiber (PMF) by the use of digital holographic microtomography. First, digital holography (DH) in microscopy configuration is used to record complex transmitted fields under various angles of incidence, and then the Fourier diffraction tomography algorithm is applied to reconstruct the 3-D refractive index (RI) distribution of the PMF. According to the 3-D map of RI, we can further get geometric parameters of the PMF by the related edge detection algorithm of image processing. The experimental results show that, the diffraction tomography algorithm is superior to the reconstruction algorithm based on Fourier slice theorem in terms of exhibiting reasonable RI distribution and respecting the dimensions of the PMF. It provides a new way for the non-destructive micromeasurement of the PMF. [ABSTRACT FROM AUTHOR]

A noninterferometric technique used to measure the diffusion coefficients of transparent liquid solutions is reported. This technique uses a white light source and a diffusion cell, with an artificially developed fringe pattern of dark and white stripes at its entrance. As the diffusion process takes place in the cell, the light passing through this nonuniform refractive index medium will bend toward the higher refractive index region, which results in a fringe shift. This shift in the fringe pattern at different times is recorded in a personal computer (PC) using a CCD camera for the calculation of diffusion coefficients. The fringe shift is calculated after skeletonization and linear fit of the captured fringe system. The diffusion coefficient of different concentrations of ammonium dihydrogen phosphate was determined using the proposed technique and the measured values lay within 1% of the reported values. Detailed theoretical and experimental analyses with a comparison of other existing results are discussed. [ABSTRACT FROM AUTHOR]

An instantaneous three-dimensional imaging technique using a chirped supercontinuum and an ultrafast optical Kerr gate, in which a sapphire plate and a TeO2-ZnO-Na2O oxide glass were used to generate the chirped supercontinuum and the ultrafast optical Kerr gate, respectively, is demonstrated. This technique is applicable to ultrafast shape measurement, such as shape imaging of moving objects, or imaging of laser- induced refractive index changes in transparent media. [ABSTRACT FROM AUTHOR]

We present a novel off-axis XR concentrator design that enables a high efficiency energy collection while avoiding the shadowing problem encountered in the designs of symmetry XR type concentrator. Combining with a 1cm2 multi-junction solar cell, the off-axis XR concentrator is able to achieve high optical efficiency of the photovoltaic system. The concentrator design is performed based on the non-imaging optic principle, with one reflective mirror (X) and one refractive lens (R). Both surfaces of the reflective and refractive element are of freeform shapes and fitted as freeform expression in the design analysis. The concentrator has concentration ratio greater than 500× and acceptance angle greater than 2°. A square homogenizing irradiance distribution on the cell is achieved with the help of a suitable rob. The tolerance of the system is analyzed. The results show that the high concentration ratio and greater acceptance angle relax all optical and mechanical tolerances reduce the production and operation cost. [ABSTRACT FROM AUTHOR]

Abstract: The principle of all-optical logical operations utilizing the unique nonlinear optical properties of a protein was demonstrated by a logic gate constructed from an integrated optical Mach–Zehnder interferometer as a passive structure, covered by a bacteriorhodopsin (bR) adlayer as the active element. Logical operations were based on a reversible change of the refractive index of the bR adlayer over one or both arms of the interferometer. Depending on the operating point of the interferometer, we demonstrated binary and ternary logical modes of operation. Using an ultrafast transition of the bR photocycle (BR-K), we achieved high-speed (nanosecond) logical switching. This is the fastest operation of a protein-based integrated optical logic gate that has been demonstrated so far. The results are expected to have important implications for finding novel, alternative solutions in all-optical data processing research. [Copyright &y& Elsevier]

Abstract: The Spectral Airglow Temperature Imager is an instrument for ground-based spectroscopic measurements of the night-glow atmosphere emissions. This instrument was developed specially for gravity wave investigation. The measured airglow spectra are matched to synthetic spectra calculated in advance for determination of the temperature in the mesopause region where the radiation maximum of some О2 emissions is situated. The synthetic spectra are transformed into a format which corresponds to the measured spectra in order to be matched. This transformation is based on the known values of the refractive index and the central wavelength of the interference filter used. A substantial part of the processing algorithms of the SATI images is connected with determination of these two filter parameters. The results of the original and newly-proposed algorithms for filter parameter calculation and their importance for the final results for temperature determination on the basis of the О2 (864–868nm) emission measurements are presented. Considerable systematic differences (∼20K) between temperatures at different points in the mesopause retrieved by the two algorithms are established. The advantage of the proposed algorithm over the original one is illustrated by retrieved rotational temperatures and by lower error values. Furthermore, the irregular errors in the nocturnal variation of the temperature retrieved by the original algorithm are absent when the proposed approach is applied. The error investigation in the calculations and the stability of the individual components of the processing algorithms and the calculation models may be helpful in achieving better results and enhancing the potentialities of the SATI instrument. [Copyright &y& Elsevier]

Abstract: Combining Support Vector Machine (SVM) with wavelet analysis, we constructed wavelet SVM (WSVM) classifier based on wavelet kernel functions in Reproducing Kernel Hilbert Space (RKHS). In conventional kernel theory, SVM is faced with the bottleneck of kernel parameter selection which further results in time-consuming and low classification accuracy. The wavelet kernel in RKHS is a kind of multidimensional wavelet function that can approximate arbitrary nonlinear functions. Implications on semiparametric estimation are proposed in this paper. Airborne Operational Modular Imaging Spectrometer II (OMIS II) hyperspectral remote sensing image with 64 bands and Reflective Optics System Imaging Spectrometer (ROSIS) data with 115 bands were used to experiment the performance and accuracy of the proposed WSVM classifier. The experimental results indicate that the WSVM classifier can obtain the highest accuracy when using the Coiflet Kernel function in wavelet transform. In contrast with some traditional classifiers, including Spectral Angle Mapping (SAM) and Minimum Distance Classification (MDC), and SVM classifier using Radial Basis Function kernel, the proposed wavelet SVM classifier using the wavelet kernel function in Reproducing Kernel Hilbert Space is capable of improving classification accuracy obviously. [Copyright &y& Elsevier]

Differential image motion monitor (DIMM) is by far the most successful and the most widely used instrument for the measurement of the optical turbulence-induced seeing angle affecting big telescopes. It is actually based upon the hypothesis that refractive index fluctuations in the whole atmosphere follow the Kolmogorov energy cascade turbulence model. However, many in situ measurements show that the the optical turbulence in the atmospheric surface layer can be non-Kolmogorov. In the following is discussed, through a simple and straightforward model, the effect of a non-Kolmogorov optical turbulence, especially in the atmospheric surface layer, on the DIMM seeing angle, and its consequent disagreement with the seeing angle affecting large telescopes. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a new surface plasmon resonance (SPR) instrument based on Kretschmann configuration. This device acquires and processes the reflected SPR image of the sample by using a webcam together with an image processing algorithm that transforms the RGB image in numeric values and correlates the integrated intensity with the refractive index of the solution. Experimental signals were compared with theoretical values and it was found an excellent agreement. In addition, the applicability of the instrument was tested by measuring the refractive index of solutions in a continuous flow mode. Excellent stability and sensitivity of the signal were found in the presence of small changes of the refractive index. [ABSTRACT FROM AUTHOR]

Abstract: A method bases on beam propagation method and image processing is brought forward to reconstruct the extraordinary refractive index profile of the ion-implanted single-mode channel waveguide in lithium niobate. Channel waveguide is formed by O2+ ion implantation at three energies of (3.0, 3.6 and 4.5MeV) and respective doses of (1.8, 2.2 and 4.8)×1014 ions/cm2 in vacuum at room temperature. Only one enhanced-index mode is observed for extraordinary light at 1539nm by prism-coupling method. TRIM’98 code is used to simulate the damage profile in channel waveguide. The modes pattern of TE and TM are measured by use of end-face coupling method. [Copyright &y& Elsevier]

A new imaging technique for high-throughput surface plasmon resonance (SPR) measurements is described. It is the application of a CCD camera for simultaneous processing of two images at two different wavelengths provided by two laser diodes. The two lasers are brought to resonance by tuning of the angle of incidence so that the detection power and the dynamic range are optimized for the wavelength pair selected. Applying a special differential processing of the two images, SPR measurements can be performed near the shot noise limit taking into account the number of CCD pixels involved. It is shown that the detection limit of imaging methods can be improved significantly if the working point is set near to the reflection minimum instead of choosing the angle with the steepest slope of the reflection curve. The technique is demonstrated by simultaneous measurement of hybridization reactions of three different types of thiolated oligonucleotides in 30 small areas set by a commercial spotter. A noise level of 1.5 × 10-6 refractive index units (RIU) was obtained for single, 500 × 500 µm² reaction areas. The noise level was about 6 × 10-7 RIU when five areas were taken into account. The present arrangement and the particular spotter applied would allow simultaneous measurements of up to 400 binding reactions with a noise level of about 1.5 × 10-6 RIU. [ABSTRACT FROM AUTHOR]

The analysis of interference fringe patterns is a technique which is indispensable in estimating the shape of an object or the refractive index field of a solution from the interference fringe pattern image. In the methods proposed to date, however, satisfactory analysis has been difficult in situations where the image contains only a few fringes, the object shape is not smooth, or the target of measurement is continuously changing with time. This paper proposes the following method of analysis. The inverse cosine function (arccos function) is applied to the interference fringe pattern image after normalizing the intensity. Then the phase inversion is estimated by assuming a monotonically increasing phase. The method is a combination of simple ideas derived from the principles of interference fringe patterns, but can be used to calculate the phase for each pixel from a single interference fringe pattern image. Depending on the conditions, analysis with higher temporal and spatial resolutions than in the Fourier transform method can be achieved. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(1): 61–73, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20325 [ABSTRACT FROM AUTHOR]

We propose new instrumentation to measure the refractive index (RI) of transparent liquids as a function of temperature. The physical phenomenon used to carry out the measurement is the light refraction that occurs in transparent liquids. A width change in a reference object is produced by light refraction, which is related to the RI. Image processing was used to measure the object width using an image from a digital microscope. The instrument measures the RI from a range of 15°C to 100°C with an accuracy of 10 − 4 %. The measurement procedure was calibrated with distilled water and acetonitrile samples, and the Sellmeier and Cauchy equation was used to compare our results. Finally, as an appropriate application, the RI of lophine in a solution was measured. [ABSTRACT FROM AUTHOR]

• CUBIC-f achieves effective clearing of fragile samples such as salamander brains. • CUBIC-f allows for tracing of genetically marked fluorescent cells. • CUBIC-f and bioinformatic pipelines allow for quantification of fibre tract density. Although tissue clearing and subsequent whole-brain imaging is now possible, standard protocols need to be adjusted to the innate properties of each specific tissue for optimal results. This work modifies exiting protocols to clear fragile brain samples and documents a downstream pipeline for image processing and data analysis. We developed a clearing protocol, CUBIC-f, which we optimized for fragile samples, such as the salamander brain. We modified hydrophilic and aqueous' tissue-clearing methods based on Advanced CUBIC by incorporating Omnipaque 350 for refractive index matching. By combining CUBIC-f, light sheet microscopy and bioinformatic pipelines, we quantified neuronal cell density, traced genetically marked fluorescent cells over long distance, and performed high resolution characterization of neural progenitor cells in the salamander brain. We also found that CUBIC-f is suitable for conserving tissue integrity in embryonic mouse brains. CUBIC-f shortens clearing and staining times, and requires less reagent use than Advanced CUBIC and Advanced CLARITY. CUBIC-f is suitable for conserving tissue integrity in embryonic mouse brains, larval and adult salamander brains which display considerable deformation using traditional CUBIC and CLARITY protocols. [ABSTRACT FROM AUTHOR]

• The oxide thickness is obtained from reflectance spectra extrema. • The oxide thickness is measured also with ellipsometry and electronic images. • Neglecting the interfaces phase-shift can induce errors of 50% on the thickness. • The phase-shift has a significant impact for oxide layers thinner than 50 m. The oxide thickness of anodized titanium samples has been determined through ellipsometry, reflectance spectra extrema positions and electronic imaging. The reflectance spectra extrema position technique is applicable in the case were the oxide layer is thin enough to generate an interference phenomenon inside the oxide layer. When reflected at the air/oxide and oxide/metal interfaces, the electromagnetic field undergoes a phase-shift, which is often neglected in the literature. By comparing the oxide thickness obtained through the different techniques, it is shown that this phase-shift is not negligible for thin oxide layers. The relative error on the oxide thickness is for example of about 50% for a 17 nm thick oxide layer. By studying the discrepancy observed in the literature for the titanium and oxide layer refractive indexes, which is of about 13% in the wavelength range (350–600 nm), the error induced when neglecting the electromagnetic phase-shift is higher than the error induced by the uncertainty on the refractive indexes for oxide thicknesses below about 50 nm. [ABSTRACT FROM AUTHOR]

A single-layer SiO2 film is deposited using ion-assisted electron beam evaporation technique, and the deposited film is characterized using variable angle spectroscopic ellipsometry, UV–Vis–NIR spectrophotometer, coherence correlation interferometer, and Abbe refractometer as well as image processing techniques to investigate its optical and surface properties. The surface quality of the film in terms of average roughness, kurtosis, skewness, and power spectral density (PSD) is analyzed using interferometer and image processing. The refractive index of the SiO2 film is found to increase from 1.452 to 1.482 at 550 nm with increase in film thickness. This is corroborated by Abbe refractometer findings where the film refractive index is found to be 1.46490 and 1.48226 for a film thickness of 100 and 400 nm, respectively. The SiO2 film also results in reduction in average surface roughness from 35 nm of the uncoated substrate to 0.15 nm of the coated surface. Statistical indicators of surface quality extract from interferometric images such as kurtosis, skewness, and PSD and also exhibit sharp decline in their respective values of the coated surface as compared to the uncoated substrate indicating improvement in the surface quality after coating. [ABSTRACT FROM AUTHOR]

An X-ray tomographic imaging method is proposed that is capable of reconstructing the complex refractive index of an object from a data set that involves only a single-shot image obtained at each tomographic view angle. This method is based on a deterministic phase retrieval method from a single diffraction intensity by use of an aperture array, and so the real and imaginary components, which are independent of each other, of the complex refractive index distribution can be reconstructed without object's assumptions about negligible absorption or phase-attenuation duality, which have been frequently required in the other single-shot phase-retrieval methods for tomography. The validity of the method is shown in computer-simulated examples of three-dimensional object reconstruction. [ABSTRACT FROM AUTHOR]

Significance: Ultrasound-assisted optical imaging techniques, such as ultrasound-modulated optical tomography, allow for imaging deep inside scattering media. In these modalities, a fraction of the photons passing through the ultrasound beam is modulated. The efficiency by which the photons are converted is typically referred to as the ultrasound modulation's "tagging efficiency." Interestingly, this efficiency has been defined in varied and discrepant fashion throughout the scientific literature. Aim: The aim of this study is the ultrasound tagging efficiency in a manner consistent with its definition and experimentally verify the contributive (or noncontributive) relationship between the mechanisms involved in the ultrasound optical modulation process. Approach: We adopt a general description of the tagging efficiency as the fraction of photons traversing an ultrasound beam that is frequency shifted (inclusion of all frequency-shifted components). We then systematically studied the impact of ultrasound pressure and frequency on the tagging efficiency through a balanced detection measurement system that measured the power of each order of the ultrasound tagged light, as well as the power of the unmodulated light component. Results: Through our experiments, we showed that the tagging efficiency can reach 70% in a scattering phantom with a scattering anisotropy of 0.9 and a scattering coefficient of 4 mm − 1 for a 1-MHz ultrasound with a relatively low (and biomedically acceptable) peak pressure of 0.47 MPa. Furthermore, we experimentally confirmed that the two ultrasound-induced light modulation mechanisms, particle displacement and refractive index change, act in opposition to each other. Conclusion: Tagging efficiency was quantified via simulation and experiments. These findings reveal avenues of investigation that may help improve ultrasound-assisted optical imaging techniques. [ABSTRACT FROM AUTHOR]

A grey cast iron specimen was investigated by Beraha-I type color etching for the purpose of developing a functional model for the etching kinetics and subsequently a method which would enable the estimation of ferrite grain orientations with respect to specific directions, solely based on optical microscopy. For this, the etching process was observed real-time in a microfluidic cell and a custom image processing software was developed to interpret the color information. Scanning electron microscopy with electron backscatter diffraction (SEM-EBSD) and atomic force microscopy (AFM) were used to determine the grain orientation and the relative thickness of the developed interference layer respectively, which were used for further calculations. It was shown that in the initial phase the etching process experiences a delay, which can be connected to breaking an oxide barrier above the ferrite grains. This delay was found to be influenced by the idle time between sample preparation and the start of etching. However, it was proven that a characteristic cycle etch rate can be defined between the first interference minimum and maximum, which shows correlation with both the 〈100〉 and 〈111〉 directions and which is also independent from the delay during the initiation phase. The exact value and orientation dependence of this cycle etch rate was experimentally determined along with the refractive index of the developed film. Our method was demonstrated to be applicable for the estimation of the angle between the surface normal and the 〈100〉, 〈111〉 directions for individual ferrite grains in the cast iron specimen, with an average absolute error of 3°, by using optical microscopy only. The method is implemented and was made available in the form of a Matlab program. Unlabelled Image • A grey cast iron specimen was investigated with Beraha-I type color etching. • A microfluidic cell, optical microscopy and image processing were used to measure the color changes. • SEM-EBSD and AFM were used to measure ferrite grain orientation and developed layer thickness. • The refractive index of the developed film in function of the wavelength was determined. • A purely optical method was proposed for the quantification of ferrite grain orientation with 3o precision. [ABSTRACT FROM AUTHOR]

A single-layer SiO2 film is deposited using ion-assisted electron beam evaporation technique, and the deposited film is characterized using variable angle spectroscopic ellipsometry, UV–Vis–NIR spectrophotometer, coherence correlation interferometer, and Abbe refractometer as well as image processing techniques to investigate its optical and surface properties. The surface quality of the film in terms of average roughness, kurtosis, skewness, and power spectral density (PSD) is analyzed using interferometer and image processing. The refractive index of the SiO2 film is found to increase from 1.452 to 1.482 at 550 nm with increase in film thickness. This is corroborated by Abbe refractometer findings where the film refractive index is found to be 1.46490 and 1.48226 for a film thickness of 100 and 400 nm, respectively. The SiO2 film also results in reduction in average surface roughness from 35 nm of the uncoated substrate to 0.15 nm of the coated surface. Statistical indicators of surface quality extract from interferometric images such as kurtosis, skewness, and PSD and also exhibit sharp decline in their respective values of the coated surface as compared to the uncoated substrate indicating improvement in the surface quality after coating. [ABSTRACT FROM AUTHOR]

We propose a novel image restoration approach to eliminate the interference fringes in terahertz (THz) imaging. By making use of the information in the background of a THz image, inverse image processing is introduced under a priori knowledge about the degradation mechanism to suppress the interference. Based on a simulated interference image and the original THz image of a piece of paper coated with graphite powder, taken from our continuous THz imaging system, the interference fringes are successfully eliminated. The enhancement of the peak signal-to-noise ratio and structural similarity index is achieved, compared with the frequency domain filtering. Moreover, the inverse image processing is performed on a THz image of fresh rat brain tissue. It presents an excellent result with accurate information for the brain tissue after interference elimination. [ABSTRACT FROM AUTHOR]

A simple method of phase-and-amplitude extraction is derived that corrects for image blurring induced by partially spatially coherent incident illumination using only a single intensity image as input. The method is based on Fresnel diffraction theory for the case of high Fresnel number, merged with the space-frequency description formalism used to quantify partially coherent fields and assumes the object under study is composed of a single-material. A priori knowledge of the object’s complex refractive index and information obtained by characterizing the spatial coherence of the source is required. The algorithm was applied to propagation-based phase-contrast data measured with a laboratory-based micro-focus x-ray source. The blurring due to the finite spatial extent of the source is embedded within the algorithm as a simple correction term to the so-called Paganin algorithm and is also numerically stable in the presence of noise. [ABSTRACT FROM AUTHOR]

Phase-shifting profilometry (PSP) based 3D shape measurement is well established in various applications due to its high accuracy, simple implementation, and robustness to environmental illumination and surface texture. In PSP, higher depth resolution generally requires higher fringe density of projected patterns which, in turn, lead to severe phase ambiguities that must be solved with additional information from phase coding and/or geometric constraints. However, in order to guarantee the reliability of phase unwrapping, available techniques are usually accompanied by increased number of patterns, reduced amplitude of fringe, and complicated post-processing algorithms. In this work, we demonstrate that by using a quad-camera multi-view fringe projection system and carefully arranging the relative spatial positions between the cameras and the projector, it becomes possible to completely eliminate the phase ambiguities in conventional three-step PSP patterns with high-fringe-density without projecting any additional patterns or embedding any auxiliary signals. Benefiting from the position-optimized quad-camera system, stereo phase unwrapping can be efficiently and reliably performed by flexible phase consistency checks. Besides, redundant information of multiple phase consistency checks is fully used through a weighted phase difference scheme to further enhance the reliability of phase unwrapping. This paper explains the 3D measurement principle and the basic design of quad-camera system, and finally demonstrates that in a large measurement volume of 200 mm × 200 mm × 400 mm, the resultant dynamic 3D sensing system can realize real-time 3D reconstruction at 60 frames per second with a depth precision of 50 μm. [ABSTRACT FROM AUTHOR]

A Mach-Zehnder interferometer wavelength filter using multiple Si waveguide structure sections showing waveguide width error tolerance is reported. Analytical calculation based on the finite element method shows that the width sensitivity is reduced to 1/30 that of the conventional device. The fabricated device exhibited width sensitivity of dλ/dW = -0.09-0.05 and all the devices on different chips showed identical wavelength response for 1500-1600 nm wavelengths. [ABSTRACT FROM AUTHOR]

This manuscript proposes a two-dimensional heterogeneous imaging medium composed of an isotropic refractive index. We exploit conformal-mapping to transfer the full Maxwell fisheye into a finite circle. Unlike our previous design that requires a mirror of Zhukovski airfoil shape, this approach can work without a mirror, while offering a comparable imaging resolution. This medium may also be used as an isotropic gradient index lens to transform a light source inside it into two identical sources of null interference. A merit of this approach is reduction of the near-zero-index area from an infinite zone into a finite one, which shall ease its realization. [ABSTRACT FROM AUTHOR]

In this paper, a method of processing argon plasma images, obtained from the DC pseudo glow discharge technique, using two- and multiple-beam interference is suggested. This method is based on measuring the image fringe shift from the background interference fringes. Hence, this mapping of intensity shift is related to the electron density distribution of the argon plasma. Also, the refractive index of the plasma is computed from the electron density values. The contrast of the interferometer images in presence of plasma shift is investigated in both cases of two- and multiple-beam interference. [ABSTRACT FROM PUBLISHER]

Despite the interest in developing improved formulas for intraocular lens power calculation, there are several sources of uncertainty that may well give rise to a significant residual refractive error. Those concerning the estimation of the corneal power are reviewed. In addition, we explore the possibility of introducing changes in some unconventional parameters of the eye to compensate for defocus and illustrate their effectiveness in two cases: a natural eye and an eye that has undergone previous surgical actions (anterior refractive surgery and cataract surgery with an intraocular lens implant). The results show that changes in the refractive index, thickness, or posterior radius of the cornea have relatively little effect on the overall refractive error. However, small changes in the refractive indexes of the aqueous or the vitreous humors are highly effective, much more so than a similar amount of change in the anterior curvature of the cornea. This fact opens new and attractive possibilities to compensate for refractive error through the introduction of changes in degrees of freedom so far considered unconventional. [ABSTRACT FROM AUTHOR]