Jose Guadalupe Suarez-Romero

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.

Detecting molecular stress in metals

In a recent work we reported dependence between the hardness of steels and its refraction complex index, showing that this optical property can be taken as a measure of the electronic interaction inside the molecular structure of metals. If the molecular structure changes then the electronic interaction changes and it is observed as a modification of its refraction index. In this work we present experimental results on steel pieces thermally treated and maintained in rest in the laboratory for material stabilization. The refraction complex index showed variations through a several days period. Variations are attributed to released stresses of the material. The steel sample is thermally treated with a tempering process and tested with an optical setup. The refractive index of the sample is measured through several days, showing variations. The ratio of changes is grater in the first days, showing an exponential decaying in subsequent periods of time.

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.

Uncertainties in strain measurements with birefringence

Photoelasticity is a stress measurement method extensively used in test laboratories of materials. This method can be a reference to validate numerical calculation of stress and strain distributions, however we need to evaluate errors and uncertainties to know the reproducibility of the method in order to compare with numerical calculation. Some transparent materials present birefringence when they are stressed. In a first approximation the birefringence depends of the stress in a linear way, the proportionality constant is known as stress-optic constant. When polychromatic light is used the wavelength becomes other important parameter for the method. Therefore the stress-optic constant is a source of error and uncertainty, also the resolution of the wavelength is a second source of error and uncertainty. In this work we present an evaluation of the sources of errors and uncertainties of the photoelasticity method for stress and strain measurements.

Design of a radiance meter with predicted size of source and distance effects

In a previous work, we described the theoretical fundamentals for the design of radiance meters. There, we observed that the length between the first and the second aperture of the instrument plays an important role in the performance of the meter. Such a length is a parameter related with the instrument response to variations of the size of the source and of the distance between the instrument and the source. Such dependences are not predicted by the theory of geometrical optics, normally used in the instrument design. Even the approximation of wave optics gives a partial understanding of the propagation of optical radiation. A more general treatment, based in the theory of partial coherence, gives a better description of the propagation.

Theoretical considerations in radiometer design

This work considers typical radiometers that measure the radiance of sources or of some surface (due to reflection). The most important thing in a radiometer is its optical cavity, which defines the solid angle of measurement. In case of instruments that use lenses, lens diameter and focal length define the solid angle. Radiometer design takes care that the solid angle subtended by the optical cavity be minor that the solid angle subtended by the source to be measured, however no considerations are taken on the length of the cavity. In this work it is discussed theoretical limitation in the design of radiometers, particularly the influence of radiometer length (the cavity length). Theory of partial coherence is used to obtain the instrument function and to show how the length of the instrument affects measurements.

Homogeneity measurements of hardness standards with a nondestructive optical method

Inhomogeneity measurement is an important test of reference materials. In case of hardness reference blocks it consists of measurements at five distributed points on the surface with a test indenter. Unfortunately the test is destructive and it is not possible to use the same point for a new measurement. In this work we propose an optical method to measure the inhomogeneity of hardness standards. As we reported in a recent work, variations of hardness in a steel produces variations in their optical properties, this fact can be used to detect variations in the hardness of blocks with a non-destructive method.

Variation of optical polarization in reflected light by redistribution of electric charge in metals

In this work, the observation of phase delay changes between parallel and perpendicular components of an optical beam reflected on a metal surface is reported. Those changes have been induced by electrically charging a metal with static charge. A quasimonochromatic lineally polarized beam is directed to a piece of steel where the beam is reflected, the polarization of the reflected beam is in general elliptical. The module of each polarization component and their difference of phase are measured with an ellipsometer. For the experiments we have started by making ellipsometry measurements on a grounded steel sample, then a second measurement has been carried out on the same sample after inducing electrostatic charge, results indicate a rotation of the elliptical polarization in the beam reflected on the electrically charged sample.

Spectral response of photopic instruments with traceability to lamps

The spectral responsivity of detectors is commonly measured through the comparison with a reference detector and an optical system that provides monochromatic radiation. Such systems are designed to provide narrow bandwidth monochromatic radiation whose optical flux is generally low. These levels of optical flux are not enough to excite photopic instruments whose spectral response has to be measured. In this work we propose an optical arrangement with enough optical flux to realize such measurements. The system consists of a color temperature calibrated lamp which is the reference. The monochromatic separation is realized with a transmittance grating. The spectral distribution at the plane of the instrument is calculated, it is practically the same that the lamp except for the level of irradiance. The spectral response measured is corrected by the bandwidth of the system. Experimental results are presented and the noise-to-signal level reached in the system is discussed.

A proposal to solve the problem of lack of concordance in the measurement of temperature when using different radiators

Pyrometer calibration is a common task in most radiometry labs. When measurements are made in a wide range of temperatures, it is necessary to use different blackbody radiators to cover the whole interval. A problem that arises with this is the lack of concordance in the signals measured by the pyrometer when taken from different radiators. In a recent publication, Fourier theory is applied to measure the temperature of inhomogeneous objects, particularly periodic objects1. Those results are used to measure the temperature of the coil filament of a reference lamp (in a range from 300 K to 3300 K, approximately), considering the filament as a periodic object, which is modeled with a simple functions arrangement. Measurement verification is also presented by comparing our calculations to the experimental data of the lamps temperature.