Determination of quality and adulteration of tequila through the use of surface plasmon resonance.

In this work, the surface plasmon resonance (SPR) technique is used to determine the quality or adulteration of tequila beverages. Graphic analyses of the position and width of the SPR curve are related to the complex refractive index of the sample, showing differentiated regions where one can easily and unambiguously identify white, aged, or extra-aged tequilas, and even adulterated or low quality tequilas. The curves generated by aged and extra-aged tequilas, with respect to those obtained from white tequilas, are wider, while the resonant peak shifts towards larger angles. This behavior should be attributed to the aging process. The resonance curve is generated in 20 s, minimizing the variations of the SPR curve parameters due to temperature fluctuations.

Photonic crystal sensor based on surface waves for thin-film characterization.

A new sensor based on optical surface waves in truncated one-dimensional photonic crystals is proposed for use in determining the optical properties of metallic or dielectric thin films and bulk media. Specifically, the method of optical characterization takes into account the changes that the surface waves of a layered structure undergo when either a thin film of arbitrary material is added at the surface or the optical properties of transmission medium change. For the surface-wave excitation the Kretschmann configuration used in attenuated total reflectance is employed.

Correction masks for thickness uniformity in large-area thin films.

Experimental results from the emission of vapor sources are considered in designing correcting diaphragms to achieve a uniform thickness distribution during evaporation of thin films mounted on large-area substrate holders, in different geometric configurations.

Transmitted scattered light from a thin film with shallow random rough interfaces.

The transmitted scattered energy of plane electromagnetic waves from a thin metallic film with shallow rough interfaces bounded by two semi-infinite media is calculated. Both interfaces are modeled as independent stationary random processes with a Gaussian roughness spectrum. Scattering of light is calculated for both TM (p) or TE (s) polarizations for normal and oblique angles of incidence. An integral equation is obtained for the transmitted field based on the Rayleigh method and their solution involves Fourier coefficients, depending on the roughness profiles. We present some results for the case of a single thin metallic film in the attenuated total reflection configuration for s and p polarization around the angle of the excitation of surface-plasma waves θ(sp). The transmitted scattered intensity shows a maximum at the resonant angle θ(sp) in the case of p polarization.

Admittance of rugate filters derived from a 2 × 2 inhomogeneous matrix.

Admittance diagrams are used to analyze qualitatively and quantitatively the behavior of inhomogeneous thin films with an arbitrary refractive-index function. From this study it follows that one can treat the behavior of rugate filters by using the concept of effective refractive indices, which are associated with the phase integral in a simple way. These results are applied to the study of periodic systems, and, as expected, one can consider high and low effective refractive indices to determine the important parameters of these stop bands. With these ideas it is possible that one can deal with rugate filters more closely as homogeneous periodic systems by taking advantage of the existing theory.

Method for calculating optical coating stabilities.

The reflectivity R of a multilayer stack and its first and second derivatives with respect to the phase change are derived here by a recursive method. These equations improve the determination of stability conditions for coatings and widen the applications to treatments other than antireflection coatings, as reported by Mouchart [Appl. Opt. 16, 2486 (1977)]. Some calculations are performed on grazing incidence antireflection coatings, all-dielectric mirrors, and bandpass filters with non-quarter-wave layers.

Optical properties of parylene and its use as substrate in beam splitters.

The optical properties of a commercial parylene pellicle are obtained using a classical oscillator model with a single oscillator. Using a standard design antireflection stack and beam-splitter multilayer films coated on this pellicle, its performance is greatly improved, flattening the curve and increasing its useful spectral range.

Attenuated-total-reflection technique for the determination of optical constants.

In a glass-metal-dielectric system, it is normally impossible to determine simultaneously the complex dielectric constant, the thickness of the metal, and the corresponding parameters of a dielectric overlayer. We propose the use of the pseudo-Brewster or Abelés angle as an additional parameter to characterize simultaneously a dielectric thin-film overcoating and the metal surface parameters. We use a Kretschmann attenuated-total-reflection configuration. An admittance diagram is used to illustrate graphically the role of an absentee layer at this angle. A study of the limitations of the method is also presented.

Determination of the optical constants of MgF(2) and ZnS from spectrophotometric measurements and the classical oscillator method.

The values of the optical constants of magnesium fluoride (MgF(2)) and zinc sulfide (ZnS) thin films are obtained using a classical oscillator model and the experimental values of their spectral transmittance. Auger electron spectroscopy was performed on the samples to determine the chemical composition of the films. These materials are important in the design of filters, mirrors, and antireflection coatings for optical instrumentation. Unfortunately their properties strongly depend on evaporation conditions. The procedure described here allows direct measurement of the dispersive refractive index of the film after deposition.

Determination of (n,k) for absorbing thin films using reflectance measurements.

We propose a method for determination of the complex refractive index of absorbing materials either in bulk or film geometry by measuring its reflectivity when coated with a well-characterized transparent dielectric at two specific optical thicknesses: n(1)d(1) = lambda(0)/4 and n(1)d(1) = lambda(0)/2. The complex refractive index of the sample ñ = (n,k) is calculated for the monitoring wavelength lambda(0). The selected optical thicknesses of the coating allow the calculation of its geometrical thickness, therefore the variation of ñ with wavelength in the region where the reflectivity is measured can be determined.