A min-norm approach for estimating phase distribution in an interferogram

Phase distribution in an interferogram is usually computed from several phase shifted intensity images acquired temporally by means of a CCD camera. These phase shifts are commonly accomplished by translation of a mirror with a piezoelectric transducer (PZT). In reality the PZT motion is not exact. Thus the aim of this paper is to present a novel approach for estimating the phase steps that are imparted to the PZT in the presence of nonsinusoidal waveforms and random noise. The method functions by designing an autocovariance matrix from the intensity registered on the CCD for N data frames. The eigendecomposition of an autocovariance matrix yields the signal and noise subspaces. The phase step values are estimated pixelwise from the noise subspace. This approach provides the flexibility of using arbitrary phase steps, a feature most commonly attributed to generalized phase shifting algorithms. Once the phase steps are estimated the Vandermonde system of equations is applied to estimate the phase distribution.     

Phase recovery from a single interferogram with closed fringes by phase unwrapping

We describe a new algorithm for phase determination from a single interferogram with closed fringes based on an unwrapping procedure. Here we use bandpass filtering in the Fourier domain, obtaining two wrapped phases with sign changes corresponding to the orientation of the applied filters. An unwrapping scheme that corrects the sign ambiguities by comparing the local derivatives is then proposed. This can be done, assuming that the phase derivatives do not change abruptly among adjacent areas as occurs with smooth continuous phase maps. The proposed algorithm works fast and is robust against noise, as demonstrated in experimental and simulated data.     

Distortionless interferogram recording by use of holographic field lenses for fluid velocimetry

Two optical systems based on holographic field lenses are presented. They have been specifically designed for the CCD camera acquisition of the interferograms obtained from a fluid plane, when one uses holographic interferometry to measure fluid velocities. The use of these systems allows for easy recording of interferograms, all having the same size and position on the CCD, independent of the fluid-plane observation direction. The holographic lenses act as directional field lenses; they change the divergent beam that reaches the lens into a convergent beam that focuses on the camera aperture. These distortionless interferogram recording systems have been demonstrated in a Rayleigh-Bénard convective flow.     

Demodulation of a single interferogram by use of a two-dimensional regularized phase-tracking technique

We present a two-dimensional regularized phase-tracking technique that is capable of demodulating a single fringe pattern with either open or closed fringes. The proposed regularized phase-tracking system gives the detected phase continuously so that no further unwrapping is needed over the detected phase.     

High-precision analysis of a lateral shearing interferogram by use of the integration method and polynomials

Interferograms obtained with ordinary interferometers, such as the Fizeau interferometer or the Twyman-Green interferometer, show the contour maps of a wave front under test. On the other hand, lateral shearing interferograms show the difference between a wave front under test and a sheared wave front, that is, the inclination of the wave front. Therefore the shape of the wave front under test is reconstructed by means of analyzing the difference. To reconstruct the wave front, many methods have been proposed. An integration method is usually used to reconstruct the wave front under test rapidly. However, this method has two disadvantages: The analysis accuracy of the method is low, and part of the wave front cannot be measured. To overcome these two problems, a new, to our knowledge, integration method, improved by use of polynomials, is proposed. The validity of the proposed method is evaluated by computer simulations. In the simulations the analysis accuracy achieved by the proposed method is compared with the analysis accuracy of the ordinary integration method and that of the method proposed by Rimmer and Wyant. The results of the simulations show that the analysis accuracy of the newly proposed method is better than that of the integration method and that of the Rimmer-Wyant method.     

Obtaining a given phase shift between voltages by the beating method

Conclusions The tests carried out by us have shown that it is possible with the above beating method circuit to set a given phase difference between voltages with an error not exceeding 0.1–0.3°, providing the described precautionary measures are observed. The above method can find wide application in producing reference phase-difference generators used for checking electronic phasemeters.The majority of phasemeters intended for measuring phase differences between two voltages have a linear scale and incorporate devices for setting the zero value of the phase. In such meters only the linearity of their scale need be checked. This circumstance makes considerably less stringent the requirements for the identity of the phasedifference generator amplifying channels, since the setting of the zero value of the phase can be made by means of the tested phasemeter.If the output of one of the channels is fitted with a calibrated potential divider it also becomes possible to use the device for measuring voltages by the compensation method.Phase-difference generators with a continuous adjustment of the phase angle in a given frequency range can be used widely not only for testing purposes but also for measuring phase characteristics of amplifiers, filters, and other radio equipment, as well as for adjusting components of tracking systems, computers, and other automatic equipment.     

Kinematic and deformation parameter measurement by spatiotemporal analysis of an interferogram sequence

In recent years, optical interferometry has been applied to the whole-field, noncontact measurement of vibrating or continuously deforming objects. In many cases, a high resolution measurement of kinematic (displacement, velocity, and acceleration, etc.) and deformation parameters (strain, curvature, and twist, etc.) can give useful information on the dynamic response of the objects concerned. Different signal processing algorithms are applied to two types of interferogram sequences, which were captured by a high-speed camera using different interferometric setups: (1) a speckle or fringe pattern sequence with a temporal carrier and (2) a wrapped phase map sequence. These algorithms include Fourier transform, windowed Fourier transform, wavelet transform, and even a combination of two of these techniques. We will compare these algorithms using the example of a 1D temporal evaluation of interferogram sequences and extend these algorithms to 2D and 3D processing, so that accurate kinematic and deformation parameters of moving objects can be evaluated with different types of optical interferometry.     

Obtaining of single phase Cu–Li alloy through an electrodeposition process

An electrodeposition process to obtain Cu–Li alloy as a function of the temperature is studied. The optimal temperature for producing sheets of a single phase of copper with lithium in solid solution, without inclusions nor voids, is determined. In fact, when the electrodeposition process is performed at a temperature of 923 K, a single phase alloy of Cu–1.4 wt.% Li with a cubic Fm3m structure with a=3.624 Å is obtained.     

Structural evolution of La-Cr-O thin films: Part I. Microstructure and phase development

The structural evolution of La-Cr-O thin films and the formation mechanisms of the LaCrO₃ perovskite phase have been studied. X-ray amorphous La-Cr-O protective coatings were deposited by magnetron sputtering on metallic interconnect materials. During the annealing of the material in air a two-step phase transition from La-Cr-O to a monoclinic LaCrO₄ monazite and further to an orthorhombic LaCrO₃ perovskite phase was observed. The formation of a fine nanoporous structure is a result of the significant increase in density of the final LaCrO₃ perovskite in comparison with monazite LaCrO₄ phase. While the porous structure was not sought after for this application, these distinctive nanostructures may have numerous applications in catalysis, separation membranes or for other SOFC components.     

Demonstration of an optical isolator by use of a nonreciprocal phase shift

The experimental study of an optical isolator by use of a nonreciprocal phase shift is demonstrated. The isolator has an optical interferometer composed of tapered couplers, nonreciprocal phase shifters, and a reciprocal phase shifter. The isolator, designed for a 1.55-mum wavelength, was fabricated to investigate the characteristics of each component. The branching and coupling characteristics of the tapered coupler were measured. The nonreciprocal and reciprocal phase shifts were also evaluated. By applying an external magnetic field to the interferometer, we confirmed the nonreciprocal phase shift in the interferometric isolator.     

Improving holographic data storage by use of an optimized phase mask.

A method for improving the spectral distribution and for reducing the reconstruction error in optical holographic data storage is proposed. By use of an optimized phase mask in the input plane, the uniformity of the spectral distribution is optimized and the reconstruction error minimized. The phase mask is designed by use of amplitude-phase retrieval algorithms. Simulation results show the merits of the proposed method.     

Design of algorithms for phase measurements by the use of phase stepping

If the best phase measurements are to be achieved, phase-stepping methods need algorithms that are 112 insensitive to the harmonic content of the sampled waveform and 122 insensitive to phase-shift miscalibration. A method is proposed that permits the derivation of algorithms that satisfy both requirements, up to any arbitrary order. It is based on a one-to-one correspondence between an algorithm and a polynomial. Simple rules are given to permit the generation of the polynomial that corresponds to the algorithm having the prescribed properties. These rules deal with the location and multiplicity of the roots of the polynomial. As a consequence, it can be calculated from the expansion of the products of monomials involving the roots. Novel algorithms are proposed, e.g., a six-sample one to eliminate the effects of the second harmonic and a 10-sample one to eliminate the effects of harmonics up to the fourth order. Finally, the general form of a self-calibrating algorithm that is insensitive to harmonics up to an arbitrary order is given.     

Determination of global phase shifts between interferograms by use of an energy-minimum algorithm

A new algorithm for precise determination of the global phase shift between two interferograms is introduced. First we calculate the frame difference between the first and the second interferogram; the difference is multiplied by a properly chosen test phase factor, and then we implement a two-dimensional Fourier transform of the frame difference and calculate the energy of the first positive (or negative) diffraction order. An iterative approach is used for the test phase to ensure that the minimum energy is obtained, and then the correct phase shift value is found. This method is called the energy-minimum Fourier transform method, which is accurate and noise insensitive compared with the single-point Fourier transform method. Both the theoretical analysis and experimental results are given.     

Least-mean-squares phase unwrapping by use of an incomplete set of residue branch cuts

A new technique for the least-mean-squares (LMS) phase-unwrapping method is developed that incorporates the concept of branch cuts between phase singularities (residues), which are usually associated with the path-following gradient integration technique. These branch cuts are introduced by decomposition of the least-mean-squares unwrapped phase into two separate components. The first results from the transverse part of the wrapped phase gradient, which is induced by residues of the original phase, and the second component is due to a potential component, independent of the residues. This decomposition allows the reconstruction of phase patterns with a high level of accuracy and consistency with the initial (wrapped) phase, even when only partial knowledge of the placement of branch cuts between residues is available. We show how the residue-induced phase, ignored by conventional LMS phase estimators, is reconstructed for a given boundary-value problem. The method is illustrated with interferometric quality-control measurements of optical fiber-connector terminations and also with synthetic aperture radar interferometry. These experiments demonstrate the high accuracy of the method in practical situations in which only a limited number of branch cuts are available.     

State of the art of bioimplants manufacturing: part I

Bioimplants are becoming increasingly important in the modern society due to the fact of an aging population and associated issues of osteoporosis and osteoarthritis. The manufacturing of bioimplants involves an understanding of both mechanical engineering and biomedical science to produce biocompatible products with adequate lifespans. A suitable selection of materials is the prerequisite for a long-term and reliable service of the bioimplants, which relies highly on the comprehensive understanding of the material properties. In this paper, most biomaterials used for bioimplants are reviewed. The typical manufacturing processes are discussed in order to provide a perspective on the development of manufacturing fundamentals and latest technologies. The review also contains a discussion on the current measurement and evaluation constraints of the finished bioimplant products. Potential future research areas are presented at the end of this paper. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-017-0207-4     

Pharmaceutical applications of hot-melt extrusion: part I

Interest in hot-melt extrusion techniques for pharmaceutical applications is growing rapidly with well over 100 papers published in the pharmaceutical scientific literature in the last 12 years. Hot-melt extrusion (HME) has been a widely applied technique in the plastics industry and has been demonstrated recently to be a viable method to prepare several types of dosage forms and drug delivery systems. Hot-melt extruded dosage forms are complex mixtures of active medicaments, functional excipients, and processing aids. HME also offers several advantages over traditional pharmaceutical processing techniques including the absence of solvents, few processing steps, continuous operation, and the possibility of the formation of solid dispersions and improved bioavailability. This article, Part I, reviews the pharmaceutical applications of hot-melt extrusion, including equipment, principles of operation, and process technology. The raw materials processed using this technique are also detailed and the physicochemical properties of the resultant dosage forms are described. Part II of this review will focus on various applications of HME in drug delivery such as granules, pellets, immediate and modified release tablets, transmucosal and transdermal systems, and implants.     

Analysis of systematic errors in spatial carrier phase shifting applied to interferogram intensity modulation determination

Two-beam interferogram intensity modulation decoding using spatial carrier phase shifting interferometry is discussed. Single frame recording, simplicity of experimental equipment, and uncomplicated data processing are the main advantages of the method. A comprehensive analysis of the influence of systematic errors (spatial carrier miscalibration, nonuniform average intensity profile, and nonlinear recording) on the modulation distribution determination using automatic fringe pattern analysis techniques is presented. The results of searching for the optimum calculation algorithm are described. Extensive numerical simulations are compared with laboratory findings obtained when testing vibrating silicon microelements under various experimental conditions.     

A parallel evolution strategy for an earth imaging problem in geophysics

In this paper we propose a new way to compute a rough approximation solution, to be later used as a warm starting point in a more refined optimization process, for a challenging global optimization problem related to earth imaging in geophysics. The warm start consists of a velocity model that approximately solves a full-waveform inverse problem at low frequency. Our motivation arises from the availability of massively parallel computing platforms and the natural parallelization of evolution strategies as global optimization methods for continuous variables. Our first contribution consists of developing a new and efficient parametrization of the velocity models to significantly reduce the dimension of the original optimization space. Our second contribution is to adapt a class of evolution strategies to the specificity of the physical problem at hands where the objective function evaluation is known to be the most expensive computational part. A third contribution is the development of a parallel evolution strategy solver, taking advantage of a recently proposed modification of these class of evolutionary methods that ensures convergence and promotes better performance under moderate budgets. The numerical results presented demonstrate the effectiveness of the algorithm on a realistic 3D full-waveform inverse problem in geophysics. The developed numerical approach allows us to successfully solve an acoustic full-waveform inversion problem at low frequencies on a reasonable number of cores of a distributed memory computer.     

On the use of spectroscopic techniques for interaction studies, part I: complexation between europium and small organic ligands

In the framework of environmental studies, it is important to understand the interaction of humic substances with cations (heavy metals, radionuclides) and to determine their complexation constants in order to evaluate their potential impact on their fate. For this purpose, two techniques have been used: electrospray ionization mass spectrometry, a newly used technique in speciation studies, and time-resolved laser-induced fluorescence spectrometry, a well-known technique for such studies. As a first step, for simplification purposes and to compare both techniques, simple molecules having functional groups present in humic substances have been selected, such as acetic, glycolic, and 4-hydroxyphenylacetic acids. Both techniques have been used to obtain stoichiometries and complexation constants between these simple molecules and europium (III).