I. Pascual

New photopolymer holographic recording material with sustainable design.

Photopolymers that absorb in the visible spectrum are useful for different applications such as in the development of holographic memories, holographic optical elements or as holographic recording media. Photopolymers have an undesirable feature, the toxicity of their components and their low environmental compatibility, particularly if we analyse the life cycle of the devices made with these materials and their interaction with the environment. In this work we developed a new photopolymer with photochemical and holographic features similar to those of the standard material but with an improved design from the environmental point of view.

Comparison of peristrophic multiplexing and a combination of angular and peristrophic holographic multiplexing in a thick PVA/acrylamide photopolymer for data storage

Two different types of multiplexing are used to store 90 holograms at the same location in a polyvinyl alcoholacrylamide photopolymer material. In the first, the 90 holograms are stored using only peristrophic multiplexing, whereas in the second a combination of angular and peristrophic multiplexing is used. The results (diffraction efficiency and dynamic range, M#) obtained with these two multiplexing techniques are compared. With the first, the dynamic range was M# = 13 and with the second M# = 8. An exposure schedule method is used to calculate the exposure time necessary to store the holograms with a more uniform, higher diffraction efficiency.

Overmodulation effects in volume holograms recorded on photopolymers

Abstract Kogelnik’s coupled-wave theory has provided a well established basis for understanding how light propagates inside a volume hologram and gives an accurate approximation of the diffraction efficiency in this type of hologram. In this paper we evaluate the effects of an overmodulation of the refractive index inside the hologram, which results in a particular behavior of the angular response of diffraction efficiency. These overmodulation effects are found in photopolymers with high acrylamide concentration.

Silver Halide (Sensitized) Gelatin in Agfa-Gevaert Plates: The Optimized Procedure

Abstract Silver halide sensitized gelatin (SHSG) is one of the most promising techniques for the fabrication of transmission holographic optical elements, achieving relatively high sensitivity of photographic material with the low scattering and high light stability of dichromated gelatin. In this paper we present the optimized procedure in Agfa-Gevaert plates. Diffraction gratings with a diffraction efficiency up to 80% and a noise level of less than 1% are obtained with a sensitivity 103 times better than dichromated gelatin.

High-efficiency volume holograms recording on acrylamide and N,N'methylene-bis-acrylamide photopolymer with pulsed laser

In order to achieve a better understanding of the mechanisms of hologram formation and higher diffraction efficiencies in volume gratings stored in acrylamide based photopolymers, a crosslinker (N,N′methylene-bis-acrylamide) has been incorporated in the photopolymer to record holograms by pulsed laser exposure. The presence of this component increases the polymerization rate and refractive index modulation. The recording was performed using a holographic copying process. The original was a grating of 1000 lines/mm processed using silver halide sensitized gelatin. First, the effect of the pulse fluence was investigated. When the pulse fluence was optimized, the results obtained using the new composition of material were compared with those using the composition without a crosslinker. Using a pulsed laser at 532 nm the photopolymer without crosslinker presented diffraction efficiencies slightly less than 60%. On the other hand, when the crosslinker was introduced in the photopolymer composition, the diffraction efficiencies achieved were higher than 85%. The non-linearity of the materials response was also studied comparing the energetic sensitivity, diffraction efficiencies and index modulation of gratings recorded with pulsed and continuous laser exposure. This study was performed fitting the angular scan of each grating using Kogelniks theory.

Model for analyzing the effects of processing on recording material in thick holograms

A new model to describe the influences of chemical processing on thick holograms is presented. The model is based on three hypotheses about the behavior of holographic recording material during processing. Thickness variations and shear-type effects that are due to processing are taken into account in this model, and a new parameter, the effective thickness, is introduced. It is possible to use this thickness to express the relation that exists between the components of the grating vector before and after processing. Experimental results obtained with transmission gratings recorded in a bleached silver halide emulsion are presented and discussed.

Linearization of conservative nonlinear oscillators

A linearization method of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force which allows us to obtain a frequency–amplitude relation which is valid not only for small but also for large amplitudes and, sometimes, for the complete range of oscillation amplitudes. Some conservative nonlinear oscillators are analysed to illustrate the usefulness and effectiveness of the technique.

Holographic system for copying holograms by using partially coherent light

A method for copying holographic optical elements with partially coherent light by using a holographic system is presented. The system includes two holographic lenses that are made as thick-phase holograms on silver halide-sensitized gelatin. The geometric conditions during reconstruction of the holographic system with white light are studied and the performance of the system is analyzed by a ray-tracing technique. The spatial and temporal coherence factors for the system are > 0.9, and this indicates that it is possible to obtain good holographic elements with this holographic system. Copies of diffraction gratings and holographic lenses obtained with dichromated gelatin and photoresist as the recording material present good optical quality.

New theoretical matrix formula for intraocular lens calculation using the optimal bending factor.

ABSTRACT By applying Gaussian optics we propose a new matrix formula model for intraocular lens (IOL) calculation that yields not only IOL optical power for a particular eye but also an evaluation of the bending factor of different IOL optical designs. This option improves IOL selection and results in the best possible optical image, a function dependent on the IOLs bending factor. This formula is a new approach to IOL calculation and may be useful in designing IOLs for abnormally hyperopic or myopic eyes. Optimal IOL power and design should both be considered in IOL calculation, which may improve the optical and clinical results of IOL implantation in the aphakic patient. The radius of the cornea is assumed to be spherical, and aspherical curves of the cornea may influence the optimal “bending” or shape factor of a lens.

A two-step method for recording holographic optical elements with partially coherent light

The authors propose a two-step method which enables them to obtain transmission holographic optical elements of high diffraction efficiency as well as a good signal-to-noise relation. By means of a device using partially coherent light, a master holographic optical element can be copied in a second photosensitive material. The results which are obtained in dichromated gelatin and photoresist are comparable to those which are obtained directly.