Ricardo Marin Mallavia

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.

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.

Quantum yield and molar absorptivity for a dye photobleaching in a holographic recording material

The quantum efficiency and molar absorption coefficients of dyes are the responsible for holographic efficiency and sensitivity in a photopolymeric holographic recording material. These parameters have been obtained by fitting the experimental transmittance curves as function of time. For this using the mechanism of photo initiation an analytical expression for the transmitted intensity in a photopolymerizable holographic material has been proposed, obtaining good agreement between theory and experience.

Dye sensitization in a highly sensitive photopolymerizable system for real-time holography

The spectral sensitivity and the enhancement of the energetic sensitivity are important points to the optimization of photopolymerizable materials. We have studied a polymeric system based on polyvinylalcohol as binder, monomers as acrylamide and dihydroxyethylenbisacrylamide and a photoinitiator system composed by triethanolamine and methylene blue. This system was irradiated with an Ar+ laser tuned at 514 nm, where this material do not absorb. Obtaining diffraction efficiencies of 55% with an energetic expositions of 500 mJcm-2. A possible mechanism of initiation of the photopolymerization process has been proposed by the presence of semireduced methylene blue that has an absorption band at 520 nm.

Improving energetic sensitivity in holography with a new photopolymer containing a mixture of rose bengal and methylene blue

We present the results of the study as holographic recording material of aphotopolymerizable mixture of polyvinyl alcohol and acrylamide, with a photo initiator system formed by a 1:1 molar mixture of the anionic dye Rose Bengal (RB) and the cationic one Methylene Blue (MB), with triethanolamine as coinitiator. Under irradiation with 514 or 633 nm light and comparative conditions, photopolymers with this photo initiator system give rise to a clear sensitivity enhancement, with regard to the use of any of the dyes alone. Still higher enhancements were achieved using as absorbing component an isolated ion-pair from the 1:1 mixture of both dues, with some different properties than those of the physical 1:1 mixture of dyes. Maximum diffraction efficiencies of 35-64 percent with 30-100 mJ.cm-2, and spatial resolution of ca. 1000 lines.mm-1, could be reached. The photo initiator mechanism using either the mixture RB/MB or the isolated ion-pair RB-MB is likely based on charge-transfer processes from the excited chromophores, that seems to be favored in the case of the ion-pair.

Mechanical behavior of holographic material in high vacuum and with temperature changes

Evaluation of the mechanical properties of films of the materials currently employed for recording diffractive optical elements is very important in order to foresee their mechanical behavior during the photochemical processing following recording of the interference pattern. This will also provide information about the mechanical and thermal stability of holograms recorded on these materials, which may be tested in the different environments in which the final application of the optical elements will be used. For quantitative evaluation of these properties in an acrylamide based photopolymeric system, a study was carried out on layers of films of polyvinylalcohol and polyvinylalcohol mixed with triethanolamine. Layers coated on glass substrate were subjected to both a high vacuum and temperature changes. Real time measurements of optical path variations in the film were performed using a vacuum interferometric measurement system.

Real-time measurements of D/log-E curves in holographic emulsions: experimental results

The response curve D-Log E is the most important method to characterize photographic emulsions. In this work we present the experimental study using a real time technique that can be applied to the improvement of the holographic properties of emulsions. We have exposured an Agfa Gevaert 8E56HD emulsion with an Argon laser tuned at 514 nm. After it, we measured the transmittance curve when the emulsion was into the developer bath function of time at 20 degrees Celsius. This method gives us the possibility of study the dynamics of different developers as a function of the storage energy. It also provides a way to optimize the composition of developers function of the chemical composition, temperature and other secondary factors as superaditivity and non-linear processes.

Optimal composition of a holographic recording material

We study the effect of the addition of a crosslinking agent in a photopolymerizable matrix for real time holography. The optimization of the concentration of this component has been realized attending to the holographic parameters like energetic sensitivity and diffraction efficiency. Diffraction efficiencies near to 80 percent have been obtained with energetic exposures of 12 mJ/cm2.

Holographic photopolymer with pentaerythritol triacrylate

New holographic recording material based on photopolymerizable systems have contributed significantly to recent growth of holographic applications. Previously, we report that on photopolymerizable system with the presence of the difunctional monomer, ethylene glycol dimethacrylate improves the behavior of the system and particularly to elucidate the role played by eosin ester with oxooxime group in the production of amine initiator radicals. This comparative study has been carried out in our laboratory using differential scanning photocalorimetry and holography. The results of the new photosensitive recording material for holography indicate that this system can be used for the formation of very promising photopolymer with better performance. The aim of this work has been changed the crosslinking monomer to decrease the energetin sensitivity and know the rest of the behavior. The new photopolymerizable mixture containing pentaethritol triacrylate in the same relation with the ethylene glycol dimethacrylate mixture. A diffraction efficiency of 80% is achieved with a energetic sensitivity of 3 J/cm2 at 514 nm, and the spatial resolution is up to 2000 l/mm.