Rosa Fuentes

Study of reflection gratings recorded in polyvinyl alcohol/acrylamide-based photopolymer

High-spatial-frequency fringes associated with reflection holographic optical elements are difficult to obtain with currently available recording materials. In this work, holographic reflection gratings were stored in a polyvinyl alcohol/acrylamide photopolymer. This material is formed of acrylamide photopolymer, which is considered interesting material for optical storage applications such as holographic memories. The experimental procedure for examining the high-spatial-frequency response of this material is explained, and the experimental results obtained are presented. With the aim of obtaining the best results, the performance of different material compositions is compared.

Noise sources in silver halide volume diffuse-object holograms

Dichromated gelatin has been established as the most frequently used recording material for the production of holographic optical elements. New applications are being found for photopolymers in previously unexplored areas such as holographic interconnect systems. However, photographic emulsion from the beginning has been and continues to be the most used holographic recording material. This is due to its relatively high sensitivity and ease of processing, the availability of improved processing chemistries and commercial films, and the repeatibility of the results. We analyze different sources of noise in photographic emulsions (such as intermodulation noise, noise gratings, and nonlinear noise) and the influence of the photochemical process on those noise sources. Bleached emulsions using rehalogenating and solvent processes are considered, and silver-halide-sensitized gelatin is discussed as a medium for transmission holograms. New developers and new noise models are presented on the supposition that the nonlinear response of the recording material is due to the photochemical process.

Study of influence of ACPA in holographic reflection gratings recorded in PVA/AA based photopolymer

The performance of a holographic data storage system depends to a great extent on the quality and the physical properties of the recording medium. The storage capabilities of photopolymer materials are under constant study and for some applications a high spatial frequency material is necessary. In this work, we focus on the study of the influence of 4,4´-Azobis(4-cyanopentanoic acid) ACPA on holographic reflection gratings recorded in a polyvinyl alcohol/acrylamide-based photopolymer with the aim of recording reflection gratings with a spatial frequency of up to 5000 lines/mm. The experimental procedure used to examine the high spatial frequency response of this material is explained and the experimental results presented.

Analysis of holographic reflection gratings recorded in polyvinyl alcohol/acrylamide photopolymer

Holographic reflection gratings in a polyvinyl alcohol/acrylamide based photopolymer were stored using symmetrical geometry in three different thicknesses of the material. The advantage of symmetrical geometry is that exact expressions for transmittance, reflectance, and electric fields can be obtained analytically. Using these expressions, experimental data were fitted to obtain parameters such as refractive index modulation, spatial period of the grating, optical thickness or shrinkage of the material.

Noise gratings in bleached silver halide diffuse-object holograms

Noise gratings in diffuse-object holograms recorded as volume phase holograms in bleached silver halide emulsion are experimentally analyzed. Measurements of the diffraction efficiency and the noise of the holograms are taken. The experimental results obtained show that there is a drop not only in the diffraction efficiency but also in the noise that is due to the presence of noise gratings.

Holographic lens recorded on photopolymers: fabrication and study of the image quality

In recent years, holographic optical elements have been introduced in different applications such as high-density data storage, interconnections, spatial and temporal filters and three-dimensional displays. Simultaneously, more sensitive, efficient and durable holographic materials have been developed. Thus it is necessary to analyze the characteristics of these elements in the holographic materials developed. In this paper a method to obtain holographic lenses in a photopolymer is presented. In order to obtain, reconstruct and analyze these lenses, an optical device was designed. Once the holographic lenses are obtained, the device allows us to capture the images provided by these lenses. The imaging quality of these lenses was evaluated by means of the modulation transfer function (MTF) and the contrast. Lenses of different focal lengths were recorded. The holographic lenses obtained had high diffraction efficiency and temporal stability. Moreover, the resolution was greater than that of other lenses with the same diaphragm number.

Calculation of shear angles in holographic gratings recorded in bleached silver-halide emulsions

Shearing phenomena in holographic gratings formed in bleached silver-halide emulsions due to chemical processing are evaluated. These effects are introduced because of the inability of emulsion-thickness changes to explain the anomalous detuning of the peak diffraction efficiency from the expected Bragg condition. Experimental results obtained with transmission and reflection gratings are presented and discussed considering shearing effects, and the values of the shear angles calculated from the Bragg-angle deviation measurements are also provided. In order to separate the shearing phenomenon and the shrinkage of the emulsion layer, a rehalogenating bleach without fixing is used because this bleach bath introduces a minimal change in the thickness of the emulsion. The influences of exposure, spatial frequency and slant angle on shear angles are briefly analyzed and discussed.

Copying computer-generated-holographic interconnects by the use of partially coherent light

Dichromated gelatin, bleached photographic emulsion, photoresist, and silver halide-sensitived gelatin are studied as holographic recording materials for holographic optical interconnects. We make the analysis by using a copying process with a computer-generated interconnect, which produces 64 diffracted beams on axis, as a master. The experimental results obtained confirm that it is possible to obtain copies in which we improve the performance of the master.

Volume influence on intermodulation noise of dielectric diffuse-object holograms.

The influence of recording material thickness on intermodulation noise is analyzed in phase holograms of diffuse objects; an increase in the signal-to-noise ratio is observed. However the intermodulation noise is independent of the thickness when there is high density before bleaching.

Noise gratings in thick-phase holographic lenses

An experimental analysis of noise gratings in holographic lenses is presented. Lenses are recorded as thick-phase holograms in bleached silver halide emulsion. The authors calculated noise grating efficiency by using the diffraction efficiency in points across a lens diameter. They show that due to presence of noise gratings, it is necessary to change the readout geometry of lenses with respect to the recording geometry in order to achieve maximum diffraction efficiency. This change gives rise to aberrations. The root mean square of the wavefront aberration on the entire surface of the lens is calculated for the holographic lens analyzed experimentally.