Holographic Sensor Based on Bayfol HX200 Commercial Photopolymer for Ethanol and Acetic Acid Detection.

This paper presents a holographic sensor based on reflection holograms recorded in the commercial photopolymer Bayfol® HX 200. The recording geometry and index modulation of the hologram were optimised to improve accuracy for this specific application. The sensor was subjected to tests using various analytes, and it exhibited sensitivity to acetic acid and ethanol. The measurements revealed a correlation between the concentration of the analyte in contact with the sensor's surface and the resulting wavelength shift of the diffracted light. The minimum detectable concentrations were determined to be above 0.09 mol/dm3 for acetic acid and 5% (v/v) for ethanol. Notably, the sensors demonstrated a rapid response time. Given that ethanol serves as a base for alcoholic beverages, and acetic acid is commonly found in commercial vinegar, these sensors hold promise for applications in food quality control.

Contribution to the Improvement of the Correlation Filter Method for Modal Analysis with a Spatial Light Modulator.

Modal decomposition of light is essential to study its propagation properties in waveguides and photonic devices. Modal analysis can be carried out by implementing a computer-generated hologram acting as a match filter in a spatial light modulator. In this work, a series of aspects to be taken into account in order to get the most out of this method are presented, aiming to provide useful operational procedures. First of all, a method for filter size adjustment based on the standard fiber LP-mode symmetry is presented. The influence of the mode normalization in the complex amplitude encoding-inherent noise is then investigated. Finally, a robust method to measure the phase difference between modes is proposed. These procedures are tested by wavefront reconstruction in a conventional few-mode fiber.

Full modeling and experimental validation of cylindrical holographic lenses recorded in Bayfol HX photopolymer and partly operating in the transition regime for solar concentration.

Concentrating photovoltaics for building integration can be successfully carried out with Holographic Optical Elements (HOEs) because of their behavior analogous to refractive optical elements and their tuning ability to the spectral range that the photovoltaic (PV) cell is sensitive to. That way, concentration of spectral ranges that would cause overheating of the cell is avoided. Volume HOEs are usually chosen because they provide high efficiencies. However, their chromatic selectivity is also very high, and only a small part of the desired spectral range reaches the PV cell. A novel approach is theoretically and experimentally explored to overcome this problem: the use of HOEs operating in the transition regime, which yield lower chromatic selectivity while keeping rather high efficiencies. A model that considers the recording material's response, by determining the index modulation reached for each spatial frequency and exposure dosage, has been developed. It has been validated with experimental measurements of three cylindrical holographic lenses with different spatial frequency ranges recorded in Bayfol HX photopolymer. Simulations of systems comprising two lenses and a mono-c Si PV cell are carried out with the standard AM 1.5D solar spectrum. Promising results are obtained when using the system with lower spatial frequencies lenses: a total current intensity equal to 3.72 times the one that would be reached without the concentrator.

Characterization of volume holographic optical elements recorded in Bayfol HX photopolymer for solar photovoltaic applications.

Volume Holographic Optical Elements (HOEs) present interesting characteristics for photovoltaic applications as they can select spectrum for concentrating the target bandwidth and avoiding non-desired wavelengths, which can cause the decrease of the performance on the cell, for instance by overheating it. Volume HOEs have been recorded on Bayfol HX photopolymer to test the suitability of this material for solar concentrating photovoltaic systems. The HOEs were recorded at 532 nm and provided a dynamic range, reaching close to 100% efficiency at 800 nm. The diffracted spectrum had a FWHM of 230 nm when illuminating at Bragg angle. These characteristics prove HOEs recorded on Bayfol HX photopolymer are suitable for concentrating solar light onto photovoltaic cells sensitive to that wavelength range.

Broadband behavior of transmission volume holographic optical elements for solar concentration.

A ray tracing algorithm is developed to analyze the energy performance of transmission and phase volume holographic lenses that operate with broadband illumination. The agreement between the experimental data and the theoretical treatment has been tested. The model has been applied to analyze the optimum recording geometry for solar concentration applications.

Holographic optical element to generate achromatic vortices.

A compound holographic optical element to generate achromatic vortices with high efficiency, based on the combination of two volume phase holograms, is designed and constructed. This element is compact and easy to align. It has high damage threshold, so it can be used with ultraintense laser pulses.

Characterization of transmission volume holographic gratings recorded in Slavich PFG04 dichromated gelatin plates.

We characterize Slavich PFG-04 dichromated gelatin plates to make transmission volume holographic elements recorded with a 532 nm laser source, obtaining high efficiency gratings with a high signal to noise ratio. The linear dynamic range of the material is studied by measuring the efficiency of multiplexed gratings. Results obtained are applied to the recording of holographic elements with high efficiency when they are illuminated with a 800 nm light source.

Anamorphic white light Fourier processor with holographic lenses.

Two anamorphic and achromatic Fourier processors were designed and constructed using diffractive and refractive cylindrical lenses. The diffractive lenses are holographic lenses recorded on silver halide material. In both processors the achromatic one-dimensional Fourier transform plane was obtained with two holographic lenses and one refractive cylindrical lens. The image with the same magnification in both directions at the output plane was formed with two different combinations of lenses. The differences between the two processors are analyzed, and in both cases the chromatic aberration in the Fourier plane and in the output plane is evaluated. Even though single cylindrical refractive lenses were used to image in one direction, good results were obtained.

Zero reference signal for displacement measuring systems by use of speckle.

An optical method for generating a reference signal for an incremental displacement measurement system is proposed. We achieved this zero reference signal by comparing two speckle patterns arriving from two symmetric diffusers, which are used as natural random codes that are identical only when the reading head is located equidistantly between the diffusers. The comparison of the speckles is obtained either by interference, as in a Michelson interferometer, or by intensity correlations.

Partitioned-field holographic lenses composed of three noncentered uniaxial systems.

Partitioned-field uniaxial volume holographic lenses increase the image fields of holographic volume lenses that are limited by angular selectivity. The efficiency and aberrations of one of these systems consisting of two overlapping uniaxial noncentered lenses were reported previously [Appl. Opt. 38, 4011 (1999)]. In the present study we present theoretical and experimental extensions of these systems to three overlapping lenses, showing how the dynamic range of the recording material can cause an important decrease in efficiency when several gratings are superposed on the same plate.

Silver halide sensitized gelatin process effects in holographic lenses recorded on Slavich PFG-01 plates.

In this work we study the feasibility of using silver halide sensitized gelatin based on PFG-01 (Slavich) emulsions to construct uniaxial compound lenses. This processing is able to introduce variations in the thickness and refractive index of the emulsion. We prove that these changes are not sufficient to provide the observed variations in Bragg conditions in the reconstruction and that a shear-type effect must exist to explain the performance of processed emulsions. We study the characteristics of a compound lens, obtaining acceptable image quality, good resolution, and the typical field limitation of volume holographic elements.

Partitioned-field uniaxial holographic lenses.

The efficiency and aberration of partitioned-field uniaxial volume holographic compound lenses are theoretically and experimentally studied. These systems increase the image fields of holographic volume lenses, limited by the angular selectivity that is typical of these elements. At the same time, working with uniaxial systems has led to a decrease in aberration because two recording points (that behave as aberration-free points) are used. The extension of the image field is experimentally proved.