Person: Sánchez Brea, Luis Miguel
Loading...
First Name
Luis Miguel
Last Name
Sánchez Brea
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Óptica
Area
Optica
Identifiers
39 results
Search Results
Now showing 1 - 10 of 39
Item Effect Of Noise In The Estimation Of Magnitudes With Spatial Dependence: A Spatial Statistics Technique Based On Kriging(Noise and Fluctuations, 2005) Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio; González, T.; Mateos, J.; Pardo, D.Kriging is a family of linear methods for the estimation of physical quantities with spatial dependence which are optimal in the squared minima sense. To perform the interpolation, kriging considers, in addition to the value and location of the observations, the spatial correlation of the quantity by means of variogram, the random fluctuations of the measured magnitude and the resolution of the measuring devices. The traditional way kriging equations are solved involves the resolution of inverse of great matrices, so that it is normally quite time consuming. Comparing the uncertainty obtained with kriging (for magnitudes with spatial dependence) with standard techniques for uncertainty estimation, we have seen that for the case of regular sampling, the uncertainty estimation can be computed as a convolution.Item Uncertainty Estimation by Convolution Using Spatial Statistics(IEEE Transactionns on Image Processing, 2006) Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioKriging has proven to be a useful tool in image processing since it behaves, under regular sampling, as a convolution. Convolution kernels obtained with kriging allow noise filtering and include the effects of the random fluctuations of the experimental data and the resolution of the measuring devices. The uncertainty at each location of the image can also be determined using kriging. However, this procedure is slow since, currently, only matrix methods are available. In this work, we compare the way kriging performs the uncertainty estimation with the standard statistical technique for magnitudes without spatial dependence. As a result, we propose a much faster technique, based on the variogram, to determine the uncertainty using a convolutional procedure. We check the validity of this approach by applying it to one-dimensional images obtained in diffractometry and two-dimensional images obtained by shadow moire.Item Double grating systems with one steel tape grating(Optics Communications, 2008) Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioSteel tape gratings are used in different metrology applications. As the period of these gratings was large (around 100μm,), its analytical study has been performed, up to date, using a geometrical approach. Nowadays, steel tape gratings can be manufactured with lower periods, around 20–40 μm, and diffractive effects must be taken into account. Also, due to the roughness of the surface, statistical techniques need to be considered to analyze their behavior. In this work, an analysis of the pseudo-imaging formation in a double grating system including one steel tape grating is performed. In particular Moiré and Lau configurations are analyzed. We have found that roughness significantly affects to Moiré configuration. However, its effect is negligible in Lau configuration. Generalized grating imaging configuration is also studied in depth. It is shown that roughness does not affect to the contrast of pseudoimages, but it modifies their depth of focus.Item Estimation of the standard deviation in three-dimensional microscopy by spatial statistics(Journal of Microscopy, 2005) Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioUsually, the calibration process for three-dimensional microscopy involves the use of a reference flat surface. The random fluctuations of the topographic image for this reference surface are used for determining the uncertainty of the microscope. When the sample material or the measuring conditions of the microscope are modified (such as the objective used in a confocal microscope, or the tip in an atomic force microscope), the measuring conditions vary and thus a new calibration is required. In this work, a technique based on spatial statistics methods (more specifically, the variogram function) is proposed to determine accurately the standard deviation for three-dimensional microscopy that does not require a reference flat surface and therefore eliminates the need for a previous calibration process of this parameter.Item Near field of stacked diffraction gratings(Optik, 2013) Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioWe obtain a general analytical formulation for determining the near field produced by N diffraction gratings disposed in stack using a scalar approximation. Parameters of the gratings such as type-amplitude/phase-, fill factors, periods and relative positions between gratings along the x and y axes are considered. The obtained formulation is useful for analyzing problems which involve several diffraction gratings, such as optical encoders since it is computationally faster than integral formulations. Finally, analytical results are compared with numerical simulations based on the Rayleigh–Sommerfeld equation.Item Histogram-based method for contrast measurement(Applied Optics, 2000) Quiroga Mellado, Juan Antonio; Sánchez Brea, Luis Miguel; García Botella, Ángel; Bernabeu Martínez, EusebioA histogram-based technique for robust contrast measurement is proposed. The method is based on fitting the histogram of the measured image to the histogram of a model function, and it can be used for contrast determination in fringe patterns. Simulated and experimental results are presented.Item Optimal achromatic wave retarders using two birefringent wave plates: reply(Applied Optics, 2013) VilasPrieto, José Luis; Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioThis reply attempts to cast some more light on the achromatic systems composed by wave plates, in particular to the calculus of the overall retardation and the use of the Jones matrix equivalence theorem. An equivalent expression for the overall retardation of the system in terms of the trace is also givenItem Optical technique for the automatic detection and measurement of surface defects on thin metallic wires(Applied Optics, 2000) Sánchez Brea, Luis Miguel; Siegmann, Philip; Rebollo, María Aurora; Bernabeu Martínez, EusebioIn industrial applications of thin metallic wires it is important to characterize the surface defects of the wires. We present an optical technique for the automatic detection of surface defects on thin metallic wires (diameters, 50–2000 µm) that can be used in on-line systems for surface quality control. This technique is based on the intensity variations on the scattered cone generated when the wire is illuminated with a beam at oblique incidence. Our results are compared with those obtained by atomic-force microscopy and scanning-electron microscopy.Item Variogram-based method for contrast measurement(Applied Optics, 2007) Sánchez Brea, Luis Miguel; Torcal Milla, Francisco José; Bernabeu Martínez, EusebioWe present a technique for determining the contrast of an intensity distribution in the presence of additive noise and other effects, such as undesired local amplitude or offset variations. The method is based on the variogram function. It just requires the measurement of the variogram at only four points and, as a consequence, it is very fast. The proposed technique is compared with other standard techniques, showing a reduction in the error of the contrast measurement.Item Detection and measurement of waviness on thin metallic wires(Applied Optics, 2004) Tejeda, César; Sánchez Brea, Luis Miguel; Bernabeu Martínez, EusebioWe propose a model for determining the far-field diffraction pattern of wires with waviness. Analytical solutions are obtained by means of the stationary phase method, which allows us to determine dimensional parameters such as wire diameter and waviness factor. Experimental results are presented, which are in accordance with our theoretical description.