Eusebio Bernabeu

Depolarization and Polarization Indices of an Optical System

The depolarization index and the direct and reciprocal polarization indices may be derived from the Mueller matrix of any optical system. These indices give direct information about the depolarizing and polarizing power of the optical system.

A Depolarization Criterion in Mueller Matrices

A necessary and sufficient scalar condition for a Mueller matrix M to describe a non-depolarizing optical system is obtained. By computing only one scalar parameter, it can be determined whether a given Mueller matrix M describes a non-depolarizing, or a depolarizing optical system. The following theorem is stated: a necessary and sufficient condition for a given Mueller matrix M to describe a non-depolarizing optical system is Tr(M T M) = 4m 2 00.

Measurement of the degree of salinity of water with a fiber-optic sensor

A fiber-optic sensor based on surface-plasmon resonance for the determination of the refractive index is used for measuring the degree of salinity of water. The transducing element consists of a multilayer structure deposited on a side-polished monomode optical fiber. Measuring the attenuation of the power transmitted by the fiber shows that a linear relation with the refractive index of the outer medium of the structure is obtained. The system is characterized by use of a varying refractive index obtained with a mixture of water and ethylene glycol. Experimental results show that the sensor can be used as a salinity-degree measurement device with environmental applications.

Complex beam parameter and ABCD law for non-Gaussian and nonspherical light beams

We define the width, divergence, and curvature radius for non-Gaussian and nonspherical light beams. A complex beam parameter is also defined as a function of the three previous ones. We then prove that the ABCD law remains valid for transforming the new complex beam parameter when a non-Gaussian and nonspherical, orthogonal, or cylindrical symmetric laser beam passes through a real ABCD optical system. The product of the minimum width multiplied by the divergence of the beam is invariant under ABCD transformations. Some examples are given.

Principal-component characterization of noise for infrared images

Principal-component decomposition is applied to the analysis of noise for infrared images. It provides a set of eigenimages, the principal components, that represents spatial patterns associated with different types of noise. We provide a method to classify the principal components into processes that explain a given amount of the variance of the images under analysis. Each process can reconstruct the set of data, thus allowing a calculation of the weight of the given process in the total noise. The method is successfully applied to an actual set of infrared images. The extension of the method to images in the visible spectrum is possible and would provide similar results.

Phase-unwrapping algorithm for noisy phase-map processing

Automated fringe-pattern processing is important in a great number of industrial applications, such as optical data testing and quality control. One of the main problems that arises with these processes is the automated phase unwrapping of the phase map associated with the fringe pattern. Usually the phase map presents problems such as noise, and low-modulation areas. A new phase-unwrapping algorithm with high noise immunity is presented. The algorithm is easily implemented and can process arbitrary shapes. The main features of this algorithm are the use of a queue for the processing of arbitrary shapes and a selection criterion that determines which pixels are going to be processed.

Analytical expression for the complex radius of curvature tensor Q for generalized gaussian beams

Abstract An expression for the complex radius of curvature tensor describing every kind of gaussian beam is proposed. This expression can be used in the tensor ABCD law. The circular, orthogonal astigmatic and non orthogonal astigmatic beams are expressed by means of this tensor.

Optical properties of laser-deposited a-Ge films : a comparison with sputtered and e-beam-deposited films

Optical properties of amorphous semiconductor films are usually strongly dependent on deposition conditions. To the best of our knowledge, this is the first publication on optical properties of amorphous Ge films that are grown by laser-assisted deposition and measured by means of spectroscopic ellipsometry over a wide spectral range (1.43-4.59 eV). Optical properties of dc magnetron-sputtered and e-beamdeposited films are also included. Effective medium modeling is used to analyze the void fraction and the film homogeneity through the thickness. The results show that laser-deposited films and dc magnetronsputtered films are similar, both being denser, more homogeneous, and more stable than e-beamdeposited films. Transmission electron microscopy analysis shows that the results of the optical study are correlated to the film structure. These results are discussed in terms of the kinetic energy of the species involved in each deposition technique and some conclusions related to the laser-assisted deposit on process are reported.

Phase-unwrapping algorithm based on an adaptive criterion

A new algorithm for phase unwrapping of phase maps with noise or logical inconsistencies is proposed. It is based on the use of an adaptive threshold and the second difference of the locally unwrapped phase as a selection criterion for the pixels to be processed.

FOURIER TRANSFORM METHOD FOR AUTOMATIC PROCESSING OF MOIRE DEFLECTOGRAMS

In this work, a Fourier transform technique for automatic analysis of moiredeflectograms is presented. A squared grating is used to multiplex the information of the deflection in two orthogonal directions in one image. This procedure avoids the necessity of rotating the grat- ings to obtain the complete deflection information. With this method only two fringe patterns, reference and distorted, are needed to determine the complete deflection information. To deal with irregularly shaped process- ing areas, a Gerchberg extrapolation method is used. The automatic determination of the carrier as well as the size and position of the recon- struction windows permit the complete and automatic measurement of the deflection produced by an ophthalmic lens in two orthogonal direc- tions. Afterwards, the refractive power maps can be obtained. Experi- mental results obtained with a progressive addition lens are presented and comparison with measurements obtained with a commercial focime- ter are shown showing a good agreement.