Juan Carlos Martinez-Anton

Seebeck nanoantennas for solar energy harvesting

We propose a mid-infrared device based on thermocouple optical antennas for light sensing and energy harvesting applications. We numerically demonstrate that antennas are able to generate low-power dc signals by beneficing of the thermoelectric properties of the metals that constitute them. We theoretically evaluate the optical-to-electrical conversion efficiency for harvesting applications and finally discuss strategies to increase its performance. Thermocouple optical antennas therefore open the route toward the design of photovoltaic devices.

Determination of optical parameters in general film–substrate systems: a reformulation based on the concepts of envelope extremes and local magnitudes

We present a reformulation of the determination of optical parameters in general film-substrate systems. Developed for interferential films in terms of photometric magnitudes (R, T), the formalism introduced allows us to establish how many parameters can be extracted from a set of measurements and from which type of sample model. These parameters are the refractive index and the absorption of both film and substrate (i.e., ñ1 = n1-jk1 and ñ2 = n2-jk2), the thickness of the film (d), the inhomogeneity of the film (Deltan1), and the surface roughness of the interfaces (sigma1, sigma2) delimiting the film. The new formalism leads to some new analytical results and confirms others. Among the new results we have the following: (a) The mathematical condition commonly related with extremes (maxima and minima) in an interference pattern defines in fact a condition for envelope extremes. (b) The refractive index of a film can be obtained without prior knowledge of the thickness or the refractive index of the substrate (provided we have an optical interference film). (c) Absorption can be directly extracted from an interference-free magnitude T/(1-R). (d) Roughness at the inner surface, inhomogeneity in the film, and absorption are correlated in reflection spectral measurements.

Seebeck nanoantennas for the detection and characterization of infrared radiation

Arrays of metallic thermocouples in the shape of spiral nanoantennas are proposed as infrared detectors, which use the thermoelectric properties of the metallic interfaces to generate electrical DC signals. The responsivity of these types of antennas is evaluated from both theoretical and numerical perspectives pointing out its potential as infrared sensors. Moreover, the same structures can be used to characterize the state of polarization of the optical near fields with a spatial resolution comparable to the wavelength.

Enhancement of surface inspection by Moiré interferometry using flexible reference gratings

We have extended the use of shadow Moiré technique to be implemented in simple curved surfaces by using a flexible grating. Dynamic visual inspection of surface micro-damages is significantly favored by the use of well adapted pliable gratings compared to the use of flat reference gratings. The experimental set-up consists of a plastic foil with a printed Ronchi grating stretched between three points which adapts to any cylindrical or conical convex surface independently of the relative orientation grating/surface. Static quantification of defects profiles is also possible with an attached CCD camera. Visual detection of defects in the range of ~30 microm in depth is obtainable.

Wavefront measurement by solving the irradiance transport equation for multifocal systems

A method for sensing wavefronts is presented. The method is based on the resolution of the irradiance transport equation, which relates the irradiance distribution and the shape of the wavefront of a light beam propagating along a given direction. The method presents no restrictions in the locations of the measurement planes and incorporates an improved procedure to geometrically correct the acquired images to take into account the effect of ray deflection in the propagation of the irradiance distributions. With the proposed technique, we measure the wavefront at the exit pupil of a progressive addition lens and find good agreement with an alternative deflectometric method.

Automatic three-dimensional spectrogoniometer for determination of optical properties and surface parameters

An automatic three-dimensional spectrogoniometer is presented. The wavelength of ligth and angles of incidence and observation are variable, making it capable of performing different optical characterizations in an integrated way.

Classification of surface structures on fine metallic wires

In this report a classification of the main surface structures found on fine metallic wires is carried out (between ∼20 and 500 μm in diameter). For this, we have analyzed a series of wires of different metallic materials, diameters and production environments by scanning electron microscopy, atomic force microscopy, and confocal microscopy. A description and the images of the structures is given and, in addition, a nomenclature to be used by manufacturers, customers and researches is proposed. With this information the surface quality of fine metallic wires may be improved in a fabrication level. One of the objectives of this catalogue of defects is to serve as a basis for measuring the quality of the surface of the wires during the production process and the development of a measuring device for that purpose.

High performance Feussner-type polarizers based on stretched poly(ethylene-terephthalate) films

Stretched poly(ethylene-terephthalate) films appear to be an interesting optical plastic for use in polarization control devices. By means of stretching ratios its birefringence, in practice, can be tailored from ∼0 to ∼0.17. It has a very wide transmission window (∼0.32–5.70 μm) and good thermal, mechanical, and chemical properties. We propose using it for polarizers based on the Feussner design. By implementing this configuration with a biaxially stretched film, we have obtained a polarizer with an achromatic extinction ratio better than 1 part in 50 000. This is comparable with conventional Glan–Thompson polarizers but with additional advantages. The principal refractive indices of the film (in the 0.43–5.7 μm range) and the operational range of the polarizer presented are also provided.

Accuracy of the thin metallic wires diameter using Fraunhofer diffraction technique

The purpose of this paper is to improve the metallic wire diameter measurement. The size of some thin wires and slits has been achieved using the spectrogoniometer which represents good alternative system of detection. The fact that, the technique of measurement may be regarded as bringing more calibrated diameter. Since it provides wide range of detection, possibility to control the output signal readjusting a minimum of points per fringe and few image error to deal with comparing to other measurement techniques. The target-arm of detection rotated and drifted by a stepping motor of high resolution. As we know the diffraction of the thin wires using Fraunhofer technique is very suitable for an automatic control in the process of fabrication. Whereas, the more precise diameter we want the more deeper study is required (both theory and experiment). Concerning the physical approach of the phenomena, we fit our data to a polynomial of the third order. The error of each coefficient is given. The odd term presented in the polynomial function may be due to the deviations from the ideal properties of the components. Once the measurements are made, a special care of the experimental data is required in order to deduce the right diameter confining us only to the minima of the diffraction pattern. The wire diameter accuracy depends not only how good is our signal but as well how good our analysis of data.

In-line detection and evaluation of surface defects on thin metallic wires

We have developed a prototype for in-line detection of surface defects in metallic wires, specially for scratches. A simple geometrical relationship between surface topography and conical reflection, permits to correlate the defects with intensity patterns in a simple way. The presented apparatus consists basically in a grating-divided laser beam incident on angular equidistant points. A CCD and an associated optics capture the information of the whole wire perimeter at once. Analytic rudiments are provided in agreement with the experimental results.