Wavefront Calculation Research Articles

Transformation of a Plane Wavefront in Hemispherical Lenses Made of Leuco-Sapphire

An algorithm for wavefront calculation of ordinary and extraordinary waves after propagation through hemispherical components made of a uniaxial crystal is developed. The influence of frequency dispersion of n о and n e , as well as change in the direction of the optic axis of the crystal, on extraordinary wavefront in hemispheres made of from leuco-sapphire and a plastically deformed analog thereof is determined.

TrackEtching — A Java based code for etched track profile calculations in SSNTDs

A java code incorporating a user friendly GUI has been developed to calculate the parameters of chemically etched track profiles of ion-irradiated solid state nuclear track detectors. Huygen’s construction of wavefronts based on secondary wavelets has been used to numerically calculate the etched track profile as a function of the etching time. Provision for normal incidence and oblique incidence on the detector surface has been incorporated. Results in typical cases are presented and compared with experimental data. Different expressions for the variation of track etch rate as a function of the ion energy have been utilized. The best set of values of the parameters in the expressions can be obtained by comparing with available experimental data. Critical angle for track development can also be calculated using the present code. Program summaryProgram Title: TrackEtchingProgram Files doi:http://dx.doi.org/10.17632/7wb6pvpbgh.1Licensing provisions: CC0 1.0Programming language: JavaNature of problem: Calculation of the etched track profiles in ion irradiated SSNTDs is important for the application in the field of nucleopore filters and for their use as templates for nano wire fabrication.Solution method: A numerical approach, based on Huygen’s method for optical wavefront calculations has been employed. At any etching time, the etching is assumed to proceed along the normal to the etched surface. Several analytical functions are tried for the variation of the track etch velocity along the ion track as a function of the depth inside the surface and the energy/stopping power of the ion in the medium.Additional comments including Restrictions and Unusual features: The program does not generate three-dimensional profile. Provision for double sided etching will be incorporated in a later version of the code.

Classical gauged massless Rarita-Schwinger fields

We show that, in contrast to known results in the massive case, a minimally gauged massless Rarita-Schwinger field yields consistent classical and quantum theories, with a generalized fermionic gauge invariance. To simplify the algebra, we study a two-component left chiral reduction of the massless theory. We formulate the classical theory in both Lagrangian and Hamiltonian form for a general non-Abelian gauging, and analyze the constraints and the Rarita-Schwinger gauge invariance of the action. An explicit wave front calculation for Abelian gauge fields shows that wave-like modes do not propagate with superluminal velocities. The quantized case is studied in gauge covariant radiation gauge and $\Psi_0=0$ gauge for the Rarita-Schwinger field, by both functional integral and Dirac bracket methods. In $\Psi_0=0$ gauge, the constraints have the form needed to apply the Faddeev-Popov method for deriving a functional integral. The Dirac bracket approach in $\Psi_0=0$ gauge yields consistent Hamilton equations of motion, and in covariant radiation gauge leads to anticommutation relations with the correct positivity properties. We discuss relativistic covariance of the anticommutation relations, and of Rarita-Schwinger scattering from an Abelian potential. We note that fermionic gauge transformations are a canonical transformation, but further details of the transformation between different fermionic gauges are left as an open problem.

Wavefront correction in the extreme ultraviolet wavelength range using piezoelectric thin films.

A new scheme for wavefront correction in the extreme ultraviolet wavelength range is presented. The central feature of the scheme is the successful growth of crystalline piezoelectric thin films with the desired orientation on an amorphous glass substrate. The piezoelectric films show a high piezoelectric coefficient of 250 pm/V. Using wavefront calculations we show that the grown films would enable high-quality wavefront correction, based on a stroke of 25 nm, with voltages that are well below the electrical breakdown limit of the piezoelectric film.

Fast-Converging Algorithm for Wavefront Reconstruction based on a Sequence of Diffracted Intensity Images

A major advantage of wavefront reconstruction based on a series of diffracted intensity images using only single-beam illumination is the simplicity of setup. Here we propose a fast-converging algorithm for wavefront calculation using single-beam illumination. The captured intensity images are resampled to a series of intensity images, ranging from highest to lowest resampling; each resampled image has half the number of pixels as the previous one. Phase calculation at a lower resolution is used as the initial solution phase at a higher resolution. This corresponds to separately calculating the phase for the lower- and higher-frequency components. Iterations on the low-frequency components do not need to be performed on the higher-frequency components, thus making the convergence of the phase retrieval faster than with the conventional method. The principle is verified by both simulation and optical experiments.

Aberration considerations in lens tolerancing

Often the tolerancing of an optical system is performed by treating the optical system as a black box in which the designer sets tolerances for perturbations and then runs a Monte Carlo analysis to determine the as-built performance. When the effects of the perturbations are not considered, the tolerances might result tighter than necessary, proper compensation might be missed, and manufacturing cost can be increased. By acquiring aberration sensitivity for each type of perturbation, an optical engineer can increase tolerances by ad hoc compensation. An aberration sensitivity evaluation can be performed quickly and can be incorporated into the initial lens design phase. A lens designer can find what surfaces or elements within the optical system will be problematic before any time-consuming Monte Carlo run is performed. In this paper we use aberration theory of plane symmetric systems to remove, to some useful extent, the black-box tolerancing approach and to provide some insights into tolerancing. The tolerance sensitivities that are analyzed are with respect to surface tilt, center thickness, index value, and radius. To analyze these perturbations, exact wavefront calculations are performed for the following aberrations: uniform astigmatism, uniform coma, linear astigmatism, distortion I, distortion II, spherical aberration, linear coma, quadratic astigmatism, and cubic distortion. We provide a discussion about how the aberration tolerancing analysis is useful.

Clinical comparison of 6 aberrometers. Part 1: Technical specifications

To provide a detailed assessment of the techniques, technical features, and practical use of 6 aberrometers made available to our institution from September 2002 to January 2004. Department of Ophthalmology, University Hospital Antwerp, Antwerp, Belgium. A number of technical and practical parameters are listed for the Visual Function Analyzer (Tracey), the OPD-scan (ARK 10000; Nidek), the Zywave (Bausch & Lomb), the WASCA (Carl Zeiss Meditec), the MultiSpot Hartmann-Shack device, and the Allegretto Wave Analyzer including working principles, data acquisition, aberrometer alignment, wavefront calculation, and data analysis. Operator and patient comfort as well as practical advantages and disadvantages are discussed. All devices met at least half the following parameters: alignment, correction for source wavelength, data averaging, measurement quality check, and inhibition of accommodation.

The influence of diffraction in microinterferometry and microtomography of optical fibers

Interferometric measurement of two- and three-dimensional refractive index distribution in optical fibers is numerically simulated with the use of wavefront calculation method based on Hyugens–Fresnel principle. The calculation is performed for two models of fibers: homogenous and step-index multi-mode fiber. The simulation is aimed at determination of errors caused by diffraction artifacts due to microdimensions of tested objects and the presence of boundaries of media with different refractive indices. The result of simulation is methodology of increasing the accuracy of measurement in selected areas of measurement field/volume. The simulation outcomes are confirmed by the experiment.

An efficient computer program for wavefront calculation by the finite-difference method

Traveltime calculation by the finite-difference method offers a powerful tool for numerical modeling, Kirchhoff migration and VSP or crosshole tomography. This technique shows a significant advantage in first traveltime calculations as compared with ray tracing when concerned with shadow zones, high contrasts in velocity, and sharp boundaries. It eliminates the inconvenience in complicated model construction faced by ray tracing. In this paper, a FORTRAN 77 computer program is presented for wavefront propagation by the finite-difference method. It is based on the idea of Eikonal solution, Fermat's principle, Huygens' principle, and the curved wavefront assumption. This computer program successfully handles arbitrarily changing velocity, high velocity contrasts, sharp boundaries, and arbitrary survey layouts. Four examples are given (high velocity gradients in the horizontal and vertical, high velocity contrasts, and high velocity boundari where head waves are created). The results show that the computer code is accurate in traveltime calculation, stable with model varieties, efficient in computer time consumption, and friendly to use.

MOVING SOURCE PROFILING (MSP)1

ABSTRACTMoving source profiling is a modification of walk‐away vertical seismic profiling in which the source is moved along a line across a well while the signal is recorded in the well at a certain depth. The method was designed to better predict the target horizon below the drill bit and away from the well location. The method has several advantages in areas of complicated overburden.In overthrust regions, the receiver is placed below much of the complicated structure to minimize distortion of the reflected signal. The final seismic image is a depth presentation of the subsurface structure and stratigraphy based on wavefront calculations. This depth estimation is obtained without extensive processing of the recorded data. The final result is available within a few days and can help interpreters to decide if and where to sidetrack the well. The method is demonstrated using an example from the overthrust zone of the Lower Saxonian Basin and the Pompeckj's well in Northern Germany.

3D graphics and the wave theory

A continuing trend in computer representation of three dimensional synthetic scenes is the ever more accurate modelling of complex illumination effects. Such effects provide cues necessary for a convincing illusion of reality. The best current methods simulate multiple specular reflections and refractions, but handle at most one scattering bounce per light ray. They cannot accurately simulate diffuse light sources, nor indirect lighting via scattering media, without prohibitive increases in the already very large computing costs. Conventional methods depend implicitly on a particle model; light propagates in straight and conceptually infinitely thin rays. This paper argues that a wave model has important computational advantages for the complex situations. In this approach, light is represented by wave fronts which are stored as two dimensional arrays of complex numbers. The propagation of such a front can be simulated by a linear transformation. Several advantages accrue. Propagations in a direction orthogonal to the plane of a front are convolutions which can be done by FFT in O( n log n ) time rather than the n 2 time for a similar operation using rays. A typical speedup is about 10,000. The wavelength of the illumination sets a resolution limit which prevents unnecessary computation of elements smaller than will be visible. The generated wavefronts contain multiplicities of views of the scene, which can be individually extracted by passing them through different simulated lenses. Lastly the wavefront calculations are ideally suited for implementation on available array processors, which provide more cost effective calculation for this task than general purpose computers. The wave method eliminates the aliasing problem; the wavefronts are inherently spatially filtered, but substitutes diffraction effects and depth of focus limitations in its stead.