Rigorous analysis of the propagation of sinusoidal pulses in bacteriorhodopsin films.

The propagation of sinusoidal pulses in bacteriorhodopsin films has been theoretically analyzed using a complete study of the photoinduced processes that take into account all the physical parameters, the coupling of rate equations with the energy transfer equation and the temperature change during the experiment. The theoretical approach was compared to experimental data and a good concordance was observed. This theoretical treatment, can be widely applied, i.e when arbitrary pump and/or signal is used or in the case of the pump and signal beams have different wavelengths. Due to we have performed a rigorous analysis, from this treatment the corresponding two level approximation has also been analyzed for these systems.

An explanation for the non-uniform grating effects during recording of diffraction gratings in photopolymers.

The recent results reported in reference 1 have produced an increased interest in explaining deviations from the ideal behavior of the energetic variation of the diffraction efficiency of holographic gratings. This ideal behavior occurs when uniform gratings are recorded, and the index modulation is proportional to the energetic exposure. As a result, a typical sin(2) curve is obtained reaching a maximum diffraction efficiency and saturation at or below this value. However, linear deviations are experimentally observed when the first maximum on the curve is lower than the second. This effect does not correspond to overmodulation and recently in PVA/acrylamide photopolymers of high thickness it has been explained by the dye concentration in the layer and the resulting molecular weight of the polymer chains generated in the polymerization process. In this work, new insights into these deviations are gained from the analysis of the non-uniform gratings recorded. Therefore, we show that deviations from the linear response can be explained by taking into account the energetic evolution of the index modulation as well as the fringe bending in the grating.

Theoretical approach to photoinduced inhomogeneous anisotropy in bacteriorhodopsin films.

The aim of this work was to perform a complete study of the dynamic and steady-state photoinduced processes of thick bacteriorhodopsin (bR) films, taking into account all the physical parameters and the coupling of rate equations with the energy transfer equation. The theoretical approach was compared with experimental data, and good concordance was found between both sets of data. The theoretical approach shows that the values of the rate constants for solid bR films are about two or three orders of magnitude lower than those observed in solution. It can also be noted that the temperature change during the experiment had a great influence on the final values of transmittance and, consequently, on the inhomogeneous distribution along the coordinate of light propagation. The study shows that, depending on the intensity and wavelength of the pump beam, we can obtain a very inhomogeneous profile of the population densities, which implies an inhomogeneous profile of the birefringence and dichroism. Therefore, this must be taken into account in the applications described for this system.

Matrix method for the study of wave propagation in one-dimensional general media.

A matrix method which relates the field and its derivative is presented for the study of wave propagation in any type of one-dimensional media. The transfer matrix is obtained from the canonical solutions of Helmholtz equations at normal incidence. The method is applied to different optical systems like a Fabry-Perot cavity formed by uniform fiber Bragg gratings, periodic dielectric structures and different quasi-periodic structures based on Fibonacci and Thue-Morse sequences of layers with constant and variable refractive index.

Application of the Fixed Point Theorem for the solution of the 1D wave equation: comparison with exact Mathieu solutions.

A method based in the application of Fixed Point Theorem (FPT) techniques to the solution of the 1D wave equation at normal incidence for materials that present a continuous (real or complex) dielectric constant is presented. As an example, the method is applied for the calculation of the electric field, reflection and transmission spectra in volume holographic gratings. It is shown that the solution obtained using this method agrees with the exact Mathieu solutions also obtained in this paper for volume holographic reflection gratings.

Upper limits of dielectric permittivity modulation in bacteriorhodopsin films.

A theoretical study of light-induced modulation of the dielectric permittivity in bacteriorhodopsin films has been done (including B--> M and B --> Q transitions). Analysis of dielectric permittivity modulation enables us to determine the fundamental limits of BR to be used in a holographic data storage system, together with the optimum experimental and material conditions. In order to carry out this analysis, the macroscopic dielectric permittivity was related to the microscopic polarizability of the three states of BR considered (B, M and Q). This parameter was calculated using a modelization procedure that includes the effect of ASP85, TRP86, and TYR185 amino acid residues (the B3LYP/6-31+ G(*) method was used for the calculations). Good concordance between theoretical calculations and experimental data was found for the linear optical properties (absorption wavelength, transition dipole moment, and dielectric permittivity modulation). The theoretical upper limits of Deltaepsilson at 750 nm (far from the resonance of the molecule) in a randomly oriented material are about 0.01 and 0.012 for B--> M and B--> Q transitions, respectively. The values of Deltaepsilon obtained were used to simulate diffraction efficiencies (eta) of a volume phase hologram recorded in a BR film. The high absorptive losses at low wavelengths (about 625 nm ) cause an interesting behavior, since the highest Deltaepsilom do not produce the greatest eta. The highest eta is produced for a hologram thickness in the range of 900-1000 microm and working wavelength of 700-750 nm.

Anomalous D-Log E curve with high contrast developer Kodak D8 on ultra fine grain emulsion BB640.

D-Log E curves, also known as H-D curves, are used since the XIX century as a tool for describing the characteristics of silver halide emulsions. This curve has a very standard shape, with a linear region, a toe, a shoulder and a solarization region. In this work we present a distortion of the usual curve due to the action of a high contrast developer, Kodak D8, on an ultra fine grain emulsion, BB640\cite{ov04}. The solarization effect is replaced by a linear zone where developed densities increase with increasing exposures, until all silver halide present in the emulsion is reduced by developer D8 to metallic silver. Densities higher than 11 have been obtained.

Acrylamide-N,N'-methylenebisacrylamide silica glass holographic recording material.

In this paper, we describe a photopolymerizable silica glass based on acrylamide (AA) and N,N'-methylenebisacrylamide (BMA) as monomers, triethanolamine (TEA) as coinitiator and yellowish eosin (YE) as photoinitiator. We studied different compositions, analyzing the diffraction efficiency, energetic exposure and effective thickness obtained in the holographic gratings. A diffraction efficiency of 60 % with an energetic exposure of 139 mJ/cm(2) and an effective thickness of 1.1 mm were obtained. Also, by varying the photopolymerizable composition of the material diffraction efficiencies higher than 80 % can be reached with an energetic exposure of 10 mJ/cm(2) and an effective thickness of 113 microm. These values are similar to those obtained in conventional photopolymer systems in polyvinylalcohol and better than the values reached in other sol-gel compositions. Also, 9 holograms were angular multiplexed with diffraction efficiencies between 6 and 12 % and total exposure time shorter than 150 ms, with a dynamic range M/#= 2.4.

Multiplexed holographic gratings for fabricating 3D photonic crystals in BB640 photographic emulsions.

Three multiplexed holographic gratings were used to fabricate 3D photonic crystals without complete band gap using ultra-fine grain holographic emulsion as the storage material. Theoretical and experimental studies were carried out in order to characterize the crystals. Good agreement between theory and experimental results was obtained, showing that it is possible to obtain a band-pass filter for a fixed direction of illumination.

Magnification and visual acuity in highly myopic phakic eyes corrected with an anterior chamber intraocular lens versus by other methods.

PURPOSE: To calculate retinal magnification and visual acuity in highly myopic phakic eyes corrected with anterior chamber intraocular lenses (IOLs) versus correction by other methods. SETTING: Laboratory of Optics, University of Alicante, Alicante, Spain. METHODS: Relative retinal magnification (RRM) was used to study changes in retinal image size induced by different correcting systems. Relative spectacle magnification (RSM) was used to compare these systems with the emmetropic eye. The matrix method was used to calculate RRM, RSM, and visual acuity in 12 theoretical cases of myopia in eyes with axial lengths from 27.0 to 33.0 mm and corneal powers from 42.00 to 48.00 diopters. RESULTS: The RRM, RSM, and visual acuity increased as corneal power increased for a myopic eye of fixed length. Changing the plane of correction from the spectacle or cornea to the intraocular increased retinal magnification, which increased visual acuity. CONCLUSION: Visual acuity in myopic eyes corrected with an IOL will be better than that in myopic eyes corrected by other means because of the retinal magnification induced by the IOL, which increases visual acuity one line or more.

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

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 IOL's 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.

Holographic reflection gratings in photopolymerizable solgel materials.

The recording of holographic reflection gratings with a spatial frequency higher than 5400 lines/mm in photopolymerizable solgel materials is experimentally demonstrated. Diffraction efficiencies near 60% and a FWHM of 2.5 nm centered at 531.5 nm are achieved. Moreover, the effect of the energetic exposure is characterized at different recording intensities.

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.

Analysis of the holographic reciprocity law for dichromated gelatin.

The holographic reciprocity law for dichromated gelatin is investigated experimentally. The results obtained show that this law does not hold true for this material.

Influence of R-10 bleaching on latent image formation in silver halide-sensitized gelatin.

The optimization of the silver halide-sensitized gelatin process is analyzed by considering the bleaching action, the influences of the developer, and the hardening modulation process.

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.

Diffuse-object holograms in silver halide emulsions: influence of the beam ratio on the efficiency and the signal-to-noise ratio.

The influence of the beam ratio between reference and object beam intensities on the characteristics of diffuse-object holograms recorded as volume phase holograms in bleached silver halide emulsion is experimentally analyzed. Measurements of the diffraction efficiency and the signal-to-noise ratio of the holograms are taken. The experimental results presented show that when the beam ratio increases, the diffraction efficiency decreases and the signal-to-noise ratio increases; these two holographic parameters behave in this way no matter what type of processing is used.

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.

Entropy-based study of imaging quality in holographic optical elements.

A method for obtaining the best image plane for holographic optical elements by the use of the concept of entropy is described. This method is applied to in-line holographic lenses with different values of spherical aberration. Numerical results show that for holograms with large aberrations the best image plane (obtained by the use of the concept of entropy) is different from the minimum-aberration-variance plane.