We report results of measurements of optical transition energies in CdSxSe1-x nanocrystals embedded in a glass matrix. By varying annealing temperature and growth time, we obtained a series of samples with crystallite...
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We report results of measurements of optical transition energies in CdSxSe1-x nanocrystals embedded in a glass matrix. By varying annealing temperature and growth time, we obtained a series of samples with crystallite sizes from 1.8 to 12.4 nm in diameter. We carried out Raman experiments and transmission electron microscopy to determine the composition and the crystallite diameter, respectively, of the semiconductor particles. We measured absorption and electromodulation spectra to identify the quantized energy levels. Two electromodulation peaks that are due to the valence band and the split-off valence band are clearly resolved. The shape of the electromodulation spectrum is significantly affected by the heavy-hole and light-hole splitting. An analysis of the change in optical transition energies with particle size shows that it is necessary to consider the effect of finite well depth of only 1-2 eV for the conduction band.
An analytic solution for the bare cavity eigenmodes of a nonsymmetric self-filtering unstable resonator is obtained by a modal expansion in prolate functions, which is a complete and orthogonal set of eigenmodes for a...
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An analytic solution for the bare cavity eigenmodes of a nonsymmetric self-filtering unstable resonator is obtained by a modal expansion in prolate functions, which is a complete and orthogonal set of eigenmodes for a symmetric confocal stable resonator. An accurate representation within the aperture is shown to require only three terms. An efficient use of Gaussian quadrature for the various calculations is described.
A new asymptotic scheme for intensity statistics of waves in random media with a pure power-law correlation is presented. In the strong scattering regime it provides effective and accurate asymptotic expansion series ...
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A new asymptotic scheme for intensity statistics of waves in random media with a pure power-law correlation is presented. In the strong scattering regime it provides effective and accurate asymptotic expansion series for all intensity moments. The new first-order result, which is considerably more accurate than that from the existing asymptotic theory, may also serve as a starting point for useful statistical models.
This paper presents a method for organizing computations in phase-step interferometry for irregular shapes that is straightforward to program. In addition to data files, which are recorded with incremental phase steps...
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This paper presents a method for organizing computations in phase-step interferometry for irregular shapes that is straightforward to program. In addition to data files, which are recorded with incremental phase steps between the interfering beams, this method requires a mask file where the valid pixels can be distinguished from invalid pixels. For example, they may he above a known threshold. By means of a simple edge-following routine, the program moves around the perimeter of the undone portion of the shape, doing the phase calculations and changing the mask pixels to mark them done. This allows the program to move contiguously from pixels that have been done to those that have not. Modulo 2-pi-ambiguities are avoided by computing the phase differences between neighboring pixels and summing them to obtain individual pixel values.
In this paper, we discuss several iterative methods for solving the system of linear equations that arises in the process of solving a Fredholm integral equation of the first kind. When applied to the very large syste...
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In this paper, we discuss several iterative methods for solving the system of linear equations that arises in the process of solving a Fredholm integral equation of the first kind. When applied to the very large systems that arise in connection with two- or three-dimension signal reconstructions, direct methods based on the singular-value decomposition require too much computation and conventional single grid iterative schemes may converge too slowly. We have developed a multigrid scheme in which the solution is sought on a fine grid, but discretizations on a set of coarser grids are used for intermediate calculations to reduce the overall computation effort. Although the quality of the reconstruction obtained using such methods is typically not as good as that achieved using a singular-value decomposition based method, computational considerations should make multigrid methods appealing for large systems of equations.
A useful discriminant vector for pattern classification is one that maximizes the minimum separation of discriminant function values for two pattern classes. This optimality criterion can prove valuable in many situat...
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A useful discriminant vector for pattern classification is one that maximizes the minimum separation of discriminant function values for two pattern classes. This optimality criterion can prove valuable in many situations because is emphasizes the class elements that are most difficult to classify. A method for computing this discriminant vector by quadratic programming is derived. The resulting calculation scales with training set size rather than number of input variables and hence is well suited to the high dimensionality of image classification tasks. Digitized images are used to demonstrate application of the approach to two-class and multiple-class image classification tasks.
The method of path integration is applied to the analysis of a model of a graded-index waveguide taper whose refractive index varies with position z along the guide and coordinates x and y transverse to the direction ...
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The method of path integration is applied to the analysis of a model of a graded-index waveguide taper whose refractive index varies with position z along the guide and coordinates x and y transverse to the direction of propagation, as 1 - 1/2c(z)x2 - 1/2b2y2. Detailed calculations are presented for the case in which c(z) is-proportional-to 1/z2, which describes the linear taper. Comments are made about tapers corresponding to other forms of c(z). We obtain an exact closed-form solution for the propagator and coupling efficiency of a linearly tapering graded-index waveguide.
Blind deconvolution is the problem of recovering two functions from their convolution. We treat the blind-deconvolution problem under restricted conditions that the components of the convolution are Hermitian and non-...
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Blind deconvolution is the problem of recovering two functions from their convolution. We treat the blind-deconvolution problem under restricted conditions that the components of the convolution are Hermitian and non-Hermitian functions and that the support of the non-Hermitian function is known. This problem is solved by combining a method for retrieving the Fourier phase of the non-Hermitian function from a convolution with a phase-only reconstruction algorithm. The characteristic of the combined method is that the uniqueness property of its solution is understood from the theory of analytic functions. A number of results obtained from computational implementation are also presented.
Light scattering by ensembles of independently scattering, randomly oriented, axially symmetric particles is considered. The elements of the scattering matrices are expanded in (combinations of) generalized spherical ...
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Light scattering by ensembles of independently scattering, randomly oriented, axially symmetric particles is considered. The elements of the scattering matrices are expanded in (combinations of) generalized spherical functions;this is advantageous in computations of both single and multiple light scattering. Waterman's T-matrix approach is used to develop a rigorous analytical method to compute the corresponding expansion coefficients. The main advantage of this method is that the expansion coefficients are expressed directly in some basic quantities that depend on only the shape, morphology, and composition of the scattering axially symmetric particle;these quantities are the elements of the T matrix calculated with respect to the coordinate system with the z axis along the axis of particle symmetry. Thus the expansion coefficients are calculated without computing beforehand the elements of the scattering matrix for a large set of particle orientations and scattering angles, which minimizes the numerical calculations. Like the T-matrix approach itself, the method can be used in computations for homogeneous and composite isotropic particles of sizes not too large compared with a wavelength. computational aspects of the method are discussed in detail, and some illustrative numerical results are reported for randomly oriented homogeneous dielectric spheroids and Chebyshev particles. Results of timing tests are presented;it is found that the method described is much faster than the commonly used method of numerical angle integrations.
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