L. Carretero

Optimization of an acrylamide-based dry film used for holographic recording

A study of the optimization and the characteristics of a dry film photopolymerizable recording material is presented. The effects of intensity, the thickness, and the variation of the concentration of each component have been studied. Diffraction efficiencies of 80%, with energetic sensitivities of 40 mJ/cm(2), have been obtained in photosensitive films of a 35-mum thickness with a spatial frequency of 1000 lines/mm.

Theoretical and experimental study of the bleaching of a dye in a film-polymerization process

The quantum efficiency and the molar-absorption coefficients of different phenothiazine dyes are obtained by means of fitting the experimental data of transmittance as a function of time. An analytical expression for the intensity transmitted in a photopolymerizable holographic material is obtained, and good agreement between theory and experience is also achieved. The analysis of these parameters is of fundamental quantities in the photochemical characterization of holographic recording materials.

Nonparaxial diffraction analysis of Airy and SAiry beams

We theoretically analyze Airy beams by solving the exact vectorial Helmholtz equation using boundary conditions at a diffraction aperture. As result, the diffracted beams are obtained in the whole space; thus, we demonstrate that the parabolic trajectories are larger than those previously reported, showing that the Airy beams start to form before the Fourier plane. We also demonstrate the possibility of using a new type of Airy beams (SAiry beams) with finite energy that can be generated at the focal plane of the lens due to diffraction by a circular aperture of a spherical wave modified by a cubic phase. The finite energy ensured by the principle of conservation of energy of a diffracted beam.

Holography as a technique for the study of photopolymerization kinetics in dry polymeric films with a nonlinear response.

A method is reported that makes use of holography to study the kinetics of the radical photopolymerization of acrylamide in a polyvinyl alcohol when the Kogelnik theory is applied. A mechanism of unimolecular termination by the radicals that initiate the polymerization reaction is postulated to calculate the quantum yield, the molar-extinction coefficient, the index of refraction, and the thickness of the film. The conversion percentage of monomers is obtained along with the ratio of rate constants of the mechanism of polymerization from the nonlinear fit of the transmittance curves, their angular response, and the temporal evolution of diffraction efficiency. Compared with previous holographic techniques, this method has the advantage of predicting these chemical parameters using all the data points of the temporal diffraction efficiency variation rather than being restricted to the linear zone of these curves. In this way the whole reaction process, not just the initial process, is taken into account.

Highly sensitive photopolymerizable dry film for use in real time holography

A photopolymerizable holographic material has been obtained and characterized using agent N,N′-dihydroxiethylenbisacrylamide as crosslinking. A sensitivity of 5 mJ/cm2 and a diffraction efficiency around of 70% have been reached for holograms recorded at 633 nm with a spatial frequency of 1000 lines/mm. High sensitivities can be obtained with low intensities, and this is important in applications such as holographic interferometry and the fabrication of holographic optical elements.

The use of partially coherent light to reduce the efficiency of silver halide noise gratings

Abstract The noise gratings recorded in a silver halide emulsion with one or two beams of either coherent or partially coherent light are the subject of this paper. The intensity transmitted through the plates when reconstruction is done with coherent light is measured, and using this intensity as a starting point the efficiency of noise gratings is determined. The experimental results we have obtained show that the efficiency of these scatter grating structures is less when holograms are recorded using partially coherent light than when coherent light is used.

Self-induced phase gratings due to the inhomogeneous structure of acrylamide photopolymer systems used as holographic recording materials

We report the observation of self‐induced gratings or noise gratings in an acrylamide photopolymer for use in real time holography. The possibilities of this noise source as an optimization technique for this type of material are pointed out. Noise gratings in these polymer films were created upon exposure to a He–Ne laser collimated beam at 633 nm without any subsequent processing step. The influence of intensity on recording noise gratings and angular selectivity are reported showing its influence on the recording of this type of noise source in real time holographic materials.

A theoretical model for noise gratings recorded in acrylamide photopolymer materials used in real-time holography

Abstract Among the different sources of noise in holography, noise gratings have been analysed extensively in photographic emulsions owing to the granular nature of these recording materials; however, information about photopolymers is quite scarce. The effect of age on transmittance curves in a photopolymer system, used as holographic recording material, shows the appearance of noise gratings. We present a theoretical model, which explains the results for transmittance as a function of time in the presence of noise gratings recorded in an acrylamide mixture photopolymer. Good agreement between theory and experience has been observed, and the model can be used to obtain an approximate value for the diffraction efficiency of noise gratings, as well as to explain the results of age in transmittance curves.

Le Grand eye for the study of ocular chromatic aberration

In this technical note we study the prediction of ocular chromatic aberration which provides Le Grands complete theoretical eye model. Theoretical computations of the longitudinal chromatic aberration are lower than experimental results. However, we show that experimental results of the chromatic difference of position (CDP) agree with theoretical predictions. The fit of the CDP for this model is practically the same as the one obtained for the Thibos reduced eye.

Theoretical model of holographic grating formation in photopolymerizable dry films in slanted geometry

We present a model describing real-time evolution of diffraction efficiency for a slanted grating recorded in holographic photopolymers when the reading is performed with the same wavelength as the recording. This model combines initiation kinetics of polymerization and the coupled-wave theory, explaining the effects of thickness, intensity and the final modulation index. The model is validated by the fit of experimental curves of temporal diffraction efficiencies recorded at different geometries.