Juan Bautista Hurtado-Ramos

Analysis of accuracy in prism coupling methods and a proposal of two simple ways for coupling to guided waves and/or for exciting surface plasmon resonance

Abstract The stationarity of the coupling spot in relation with different shapes of couplers is discussed. The accuracy in measuring the effective index by various couplers is analyzed. Two simple methods are proposed to couple light into guided waves and/or to excite surface plasmon resonance (SPR). One uses an optical block as a coupler and the incident beam falls onto it in two perpendicular directions. This method is particularly useful for exciting SPR at an interface between metal and anisotropic dielectric media, but also can be used to couple light into guided waves. Another method does not need any coupler. The incident beam is directly launched into the sample from the sustrate side. When a thin metal film is deposited on the substrate and covered either by air or another dielectric layer, SPR can be excited at the interface of metal/air of metal/dielectric. This method can be viewed as an alternative of Kretschmann configuration.

Scattering loss measurements of evaporated slab waveguides of SiO2 and NdF3 using a prism coupler and angle-limited integrated scattering

A method for finding the attenuation coefficient of a planar or channel waveguide is described. Results for SiO2 and NdF3 waveguides were obtained, showing that the latter presents better attenuation characteristics. The influence of the prism shape on the measurements was also tested and found to result in variations in the measured attenuation coefficient. Two different locations of the waveguides were selected for the coupling, and again variations occurred, suggesting irregular thickness of the thin films. The method uses concepts based on the angle- limited integrated scattering technique and also on the well-known prism coupling method. It may be possible to make the system fully automatic.

Guided waves in thin films consisting of tilted columns deposited on anisotropic substrates: excited by a birefringent coupler

A birefringent hemispheric coupler is used to tunnel light into obliquely deposited anisotropic films consisting of tilted columns. Birefringent effects of the coupler, the films, and the substrates are studied, their influence on the phase-matching condition is analysed. Guided waves in titanium dioxide films, deposited onto BK7 glass substrates and onto silicon dioxide underlayers, are excited by using a uniaxial rutile coupler. The refractive indices and thicknesses of the films are determined from the measured coupling angles with an accuracy to the third decimal place and an uncertainty of less than ten nanometres, respectively.

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.

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.

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.

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.