Sánchez Brea, Luis Miguel

Profile Picture
First Name
Luis Miguel
Last Name
Sánchez Brea
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
UCM identifierORCIDScopus Author IDWeb of Science ResearcherIDDialnet IDGoogle Scholar ID

Search Results

Now showing 1 - 10 of 28
  • Publication
    Double grating systems with one steel tape grating
    (Elsevier Science BV, 2008-12-01) Torcal Milla, Francisco José; Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio
    Steel 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.
  • Publication
    Far field of binary phase gratings with errors in the height of the strips
    (SPIE, 2009-06-17) Rico-García, José María; Sánchez Brea, Luis Miguel
    Diffraction gratings are not always ideal but, due to the fabrication process, several errors can be produced. In this work we show that when the strips of a binary phase diffraction grating present certain randomness in their height, the intensity of the diffraction orders varies with respect to that obtained with a perfect grating. To show this, we perform an analysis of the mutual coherence function and then, the intensity distribution at the far field is obtained. In addition to the far field diffraction orders, a "halo" that surrounds the diffraction order is found, which is due to the randomness of the strips height.
  • Publication
    Variogram-based method for contrast measurement
    (The Optical Society Of America, 2007-08-01) Sánchez Brea, Luis Miguel; Torcal Milla, Francisco José; Bernabeu Martínez, Eusebio
    We 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.
  • Publication
    Optical technique for the automatic detection and measurement of surface defects on thin metallic wires
    (The Optical Society Of America, 2000-02-01) Sánchez Brea, Luis Miguel; Siegmann, Philip; Rebollo, María Aurora; Bernabeu Martínez, Eusebio
    In 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.
  • Publication
    Detection and measurement of waviness on thin metallic wires
    (The Optical Society Of America, 2004-03-01) Tejeda, César; Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio
    We 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.
  • Publication
    Uncertainty Estimation by Convolution Using Spatial Statistics
    (IEEE Institute of Electrical and Electronics Engineers, 2006-10) Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio
    Kriging 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.
  • Publication
    Diffractive performance of square Fresnel zone plates
    (Elsevier, 2009-06-14) Alda, Javier; Rico García, José María; Salgado Remacha, Francisco Javier; Sánchez Brea, Luis Miguel
    We analyze the optical behavior of square Fresnel zones plates. A theoretical analysis and numerical simulations based on the Rayleigh-Sommerfeld approach have been developed analyzing properties such as the depth of focus and the intensity of the focus in terms of the number of zones. In addition, an experimental verification has been performed using a Spatial Light Modulator to implement the designed square Fresnel zones plates.
  • Publication
    Comparison between optical techniques and confocal microscopy for defect detection on thin wires
    (Elsevier Science B. V., 2004-11-15) Siegmann, Philip; Sánchez Brea, Luis Miguel; Martínez Antón, Juan Carlos; Bernabeu Martínez, Eusebio
    Conventional microscopy techniques, such as atomic force microscopy (AFM), scanning electron microscopy (SEM), and confocal microscopy (CM) are not suitable for on-line surface inspection of fine metallic wires. In the recent years, some optical techniques have been developed to be used for those tasks. However, they need a rigorous validation. In this work, we have used confocal microscopy to obtain the topography z(x,y) of wires with longitudinal defects, such as dielines. The topography has been used to predict the light scattered by the wire. These simulations have been compared with experimental results, showing a good agreement.
  • Publication
    Determination of the optimum sampling frequency of noisy images by spatial statistics
    (The Optical Society Of America, 2005-06-01) Sánchez Brea, Luis Miguel; Bernabeu Martínez, Eusebio
    In optical metrology the final experimental result is normally an image acquired with a CCD camera. Owing to the sampling at the image, an interpolation is usually required. For determining the error in the measured parameters with that image, knowledge of the uncertainty at the interpolation is essential. We analyze how kriging, an estimator used in spatial statistics, can generate convolution kernels for filtering noise in regularly sampled images. The convolution kernel obtained with kriging explicitly depends on the spatial correlation and also on metrological conditions, such as the random fluctuations of the measured quantity, and the resolution of the measuring devices. Kriging, in addition, allows us to determine the uncertainty of the interpolation, and we have analyzed it in terms of the sampling frequency and the random fluctuations of the image, comparing it with Nyquist criterion. By use of kriging, it is possible to determine the optimum-required sampling frequency for a noisy image so that the uncertainty at interpolation is below a threshold value.
  • Publication
    Histogram-based method for contrast measurement
    (The Optical Society of America, 2000-08-10) Quiroga Mellado, Juan Antonio; Sánchez Brea, Luis Miguel; García Botella, Ángel; Bernabeu Martínez, Eusebio
    A 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.