Eduardo Tepichin-Rodriguez

Corrections of size-of-source effect and distance effect in radiometric measurements of radiance

Many optical instruments used in quality control of the optical radiation emission level of several devices are limited by the so-called size-of-source effect (SSE) as well as the distance effect (DE) when we are dealing with very accurate measurements. Different authors have studied the SSE and DE and have proposed experimental methods that provide corrections for them. We describe a general method based on the partial coherence theory that allows us to describe and calculate the SSE and DE in any radiometric system with circular apertures. We show some experimental results that verify our proposal. Additionally, as a practical example, we present the corresponding DE and SSE correction factors for a particular geometry.

Dynamic noise elimination on 2-D periodic structures using a liquid crystal display as an incoherent reconfigurable spatial source

Dynamic noise elimination in 2-D periodic structures is achieved with a liquid crystal display used as a 2-D incoherent reconfigurable source. The method, which is based on the Lau effect, shows that under certain conditions it can be used for correcting, in real time, defects dues to noise in 2-D periodic structures. Experimental verification of the noise elimination is presented.

New irradiance approach for evaluation of diffraction errors

In this work we present a solution to the problem of the cross spectral density propagated through a circular aperture in the Fresnel approximation. Our proposal is a generalization to partially coherent illumination of the classical solution of the problem of near field diffraction due to a circular aperture. Our result can be used to improve the evaluation of the diffraction errors in Radiometry. We show that our generalization contains as particular cases the ones already reported in the literature.

Hue, brightness, and saturation manipulation of diffractive colors

We describe a holographic technique suitable to manipulate the chromaticism and brightness of the diffractive colors. This technique allows us to reproduce a wide range of color sensations as true color holographic images. Experimental results that verify our proposal are included.

Numerical calculation of the Fresnel diffraction patterns for periodic objects in measurements with a two-aperture radiometer

We present numerical calculations of the Fresnel diffraction for periodic structures in an optical system with two apertures. In such a system, measurements are affected by the relation between the spatial frequency of the sample and the geometrical parameters involved (i.e., aperture diameters, radiometer-sample distance, in-plane rotation, and translation of the sample). This numerical calculation of the Fresnel diffraction enables us to establish criteria to choose the right geometrical parameters of the system to ensure invariance of the measurements when the sample is rotated or shifted. We use the theory of partial coherence to calculate the Fresnel diffraction through two successive apertures. By using the point spread function of the system, as in the theory of partial coherence, we avoid complicated statistical processes that are commonly used in this theory. We show some numerical results that verify our proposal.

Radiation pyrometric measurements with distance-to-the-source effect and size-of-the-source effect corrections

Radiation pyrometers are widely used in industries and laboratories for non-contact temperature measurement of objects. In the case of very accurate pyrometry, the measurements are affected by two effects, namely, the size-of-source effect (SSE) and the distance to the source effect (DE). The lack of accuracy in the measurements due to the SSE is associated to variations in the size of the object for a fixed measuring distance, whereas for the DE is associated to variations of the measuring distance for a fixed size of the object. In this work we present a numerical method that can be used for the calculation of corrections for both effects. In this case the method is applied to a lensless double aperture pyrometer. The method is based on the theory of partial coherence for the calculation of the energy transport through the pyrometer. The corrections can be made for sources of any size and shape and for any distance. In this case we consider sources of circular shape given our black body radiators. We present experimental results that confirm our numerical calculations.

Diffraction patterns in Fresnel approximation of periodic objects for a colorimeter of two apertures

In this work, we present a study of Fresnel diffraction of periodic structures in an optical system of two apertures. This system of two apertures was used successfully for measuring color in textile samples solving the problems of illumination and directionality that present current commercial equipments. However, the system is sensible to the spatial frequency of the periodic sample’s area enclosed in its optical field of view. The study of Fresnel diffraction allows us to establish criteria for geometrical parameters of measurements in order to assure invariance in angular rotations and spatial positions. In this work, we use the theory of partial coherence to calculate the diffraction through two continuous apertures. In the calculation process, we use the concept of point-spread function of the system for partial coherence, in this way we avoid complicated statistical processes commonly used in the partial coherence theory.

Series representation of the instrument function of a two-aperture radiometer

Recently it was reported a method to calculate the instrument function of a two-aperture radiometer which describes the energy transport through two apertures using the theory of partial coherence. The result of that work was expressed as a multiplication of a two-fold integral and its complex conjugate. In this work we solve partially this two-fold integral, particularly we introduce a semi-cicle angular integral that reduces the integration. This new representation allows a faster numerical evaluation as well as an easier interpretation of energy transport for radiometric considerations.

Novel illumination geometry for color measurements in textile samples

Color measurements in textile samples is a very well known problem, current measurement methods are repositioning-of-sample dependent. In particular, the orientation of the sample is the first parameter of discrepancies in the reproducibility of measurements, even when we use the same instrument and the same sample. In this work we propose a new optical arrangement which is insensible to rotations. Preliminary experimental results show the invariance under rotations of two-dimensional periodic samples.

Explanation of the law of conservation of radiance using the theory of partial coherence

The radiance and the law of conservation of radiance are two concepts created in an effort to explain experimental observations with extended incoherent sources. In this work we show that such observations are an effect of the partial coherence of the optical fields and that they can be explained by calculating the irradiance of the diffraction pattern of apertures with partial coherent illumination.