Time-delay of transmitted pulses with respect to the incident pulse in bacteriorhodopsin films has been studied without the use of a pump beam. Based on a modified saturable absorber model, analytical expressions of the transmitted pulse have been obtained. As a result, time delay, distortion and fractional delay have been theoretically analyzed for sinusoidal pulses with a low background.
An energetic study of focused ultrashort Gaussian beams was carried out using the Fresnel diffraction formulae
in the frequency domain. Analysis of the encircled energy at the focused plane shows that diffraction spreading
of a focused pulsed beam occurs in the limiting case of a ultrashort pulse by comparing it to a cw beam whose
frequency is ωm which strongly contributes to the diffracted intensity rather than the carrier frequency ω0.
In this work we are going to apply GPU (Graphical Processing Units) with CUDA environment for scientific calculations, concretely high cost computations on the field of digital holography. For this, we have studied three typical problems in digital holography such as Fourier transforms, Fresnel reconstruction of the hologram and the calculation of vectorial diffraction integral. In all cases the runtime at different image size and the corresponding accuracy were compared to the obtained by traditional calculation systems. The programs have been carried out on a computer with a graphic card of last generation, Nvidia GTX 680, which is optimized for integer calculations. As a result a large reduction of runtime has been obtained which allows a significant improvement. Concretely, 15 fold shorter times for Fresnel approximation calculations and 600 times for the vectorial diffraction integral. These initial results, open the possibility for applying such kind of calculations in real time digital holography.
Protein Bacteriorhodopsin (bR) is one of the most promising and widely studied biomaterials for photonic applications
like optical storage, modulation devices and photosynthetic light energy transduction. In this paper, we present the
corresponding experimental results when pH-controlled modifications of bR doped polymeric films are realized in order
to apply these systems to all-optical switching processes and technologies.
In this work, the performance of wild type bR processed in polymeric films with different pH was tested in several series
of experiments by varying the pump beam (532 nm) period of ON and OFF and analyzing the amplitude contrast and
switching time of the probe beam (633 nm). The influence of pH values on contrast ratio and switching time were also
discussed and the optimal value was found by defining a new parameter called "switching speed". As a result, the
variation of pH can be used to obtain different time of response and speed of modulation. Concretely, we find that, in
function of pH, variations of a magnitude order in contrast ratio and time response can be obtained. So, at the red region
of the probe beam, high pH values produce high transmission with flat response in the contrast ratio and a magnitude
order variation in switching time. On the other hand, at medium pH values and when high intensities are used, the
switching time and contrast ratio are better. Moreover, it is demonstrated that as a function of the wavelength of the
probe beam the transmission response curve changes. Absorption response is very important and depends on relaxation
time processes of intermediate species which are function of pH values. Therefore, these results bring the possibility for
controlling the contrast ratio and the switching time in a specific way which could be useful for different applications.
In this work, we present the analysis of a photopolymerizable system based on pyrromethene dye (PM567) acting
as a photoinitiator and HEMA as monomer both of them dissolved in a dry polymeric matrix of PMMA. Previously,
we reported the recording of diffraction gratings in this composition, resulting in diffraction efficiencies
near 60 % with exposures of 1 J/cm2 in materials with thicknesses around 500 microns. Although, the mentioned
response (best) was observed at low intensities but at higher ones lower diffraction efficiencies were reached. Furthermore,
in all the studied cases inhibition periods with asymmetrical angular selectivity curves were obtained.
Since, in order to solve the mentioned drawbacks, the aim of this work is to analyze the effect of the addition of a
crosslinking agent (PETA) in a photopolymerizable holographic material based on a pyrromethene dye (PM567)
acting as a photoinitiator and HEMA as monomer both of them dissolved in a dry polymeric matrix of PMMA.
For this, diffraction gratings were recorded at different intensities and the energetic evolution of the diffraction
efficiency as well as the observed inhibition period were studied as a function of the concentration of crosslinking
agent. Moreover, the experimental angular selectivity curves were theoretically analyzed by the model of Kubota
and Uchida, and as a result information such as the effective thickness, fringe bending and non-uniform index
modulation against the thickness of grating was obtained.
We present a holographic system that can be used to manipulate the group velocity of light pulses. The proposed
structure is based on the multiplexing of two sequential holographic volume gratings, one in transmission and the
other in reflection geometry, where one of the recording beams must be the same for both structures. Analytical
expressions were obtained for the transmittance induced at the forbidden band (spectral hole) and conditions
where the group velocity was slowed down were analyzed. Moreover, the propagation of Gaussian pulses is
analyzed in this system for a fixed reflection grating and three different transmission gratings.
Silver halide materials have occupied an important place in the recording of images. The reason is mainly given
by the high sensitivity of the recording medium, thus permitting the use of minimal levels light and hence easing
the stability problems of apparatus and the need for high powered laser equipment. When the film is exposed in
a holographic process a latent image of a diffraction grating is formed. The developing solution reduces exposed
silver halide grains to silver at a higher rate than the unexposed grains. Among the commercial emulsions,
recently good results have been reported in BB-640 photographic emulsions, since in this work we present the
experimental results related to the response of this emulsion to the interference of pulsed Gaussian beams. For
this, diffraction gratings were recorded by the interference of pulsed Gaussian beams with 120 fs of width,
76 MHz of frequency repetition and central wavelength of 790 nm, where the transmittance of this emulsion
is higher than 99%. As a result, diffraction efficiencies up to 30% were obtained with low sensitivities due to
the low absorption and grain size (18 - 20nm). The thickness of the photographic emulsions and the bleached
process has been analyzed and the sensitivity has been optimized with D8 developer.
The aim of this work is to analyze the effect of the addition or substitution of several components (coinitiator
and photoinitiator) in a photopolymerizable holographic material based on a pyrromethene dye (PM567) acting
as a photoinitiator and HEMA as monomer both of them dissolved in a dry polymeric matrix of PMMA. For
this, diffraction gratings were recorded at different intensities and the energetic evolution of the diffraction
efficiency as well as the observed inhibition period were studied as a function of the component that has been
modified (coinitiator (tert-butyl peroxybenzoate (tBPH)) or photoinitiator PM546 and PM556). Moreover, the
experimental angular selectivity curves were theoretically analyzed by the model of Kubota and Uchida, and as a
result information such as the effective thickness, fringe bending and non-uniform index modulation against the
thickness of grating was obtained. It is observed that when PM546 is used instead of PM567, better responses
for a wide range of intensities are obtained, in particular at high intensity where gratings with low fringe bending
and a relative constant index modulation against thickness is reached. When a coinitiator such as tert-butyl
peroxybenzoate (tBPH) is added to the reference composition, shorter inhibition periods are obtained with low
fringe bending but with lower diffraction efficiencies.
The multiplexing of holographic reflection gratings with a spatial frequency higher than 5400 lines/mm in photopolymerizable
sol-gel materials is experimentally demonstrated. The effect of the angular separation of the
gratings and exposure time is characterized. Moreover, 9 reflection gratings are angularly multiplexed with
diffraction efficiencies between 6 and 12% using an energy of 9 mJ/cm2 in each exposure, resulting in a dynamic
range M/# = 2.8.
Present and future of holography depends on the development of high quality holographic recording media. In
this sense, the improvement of most of the applications associated with holography can be attributed to the
optimization of the recording step in material. In this work we review holographic recording media as silver
halide, photopolymers and sol-gel in which it has been demonstrated the possibility for achieving holographic
storage and holographic optical elements. Photographic emulsions have high popularity in holographic recording,
due to the high exposure sensitivity, the high resolving power and wide range of spectral sensitivity. In this
work, recent advances in BB-640 Colorholographic photographic emulsion will be presented in transmission and
reflection holographic gratings. Moreover photopolymers have been demonstrated as a high potential material
in holographic optical storage. These materials do not need postprocessing, therefore they can be analyzed
in real time. Furthermore, photopolymers have advantage such as the possibilities to be fabricated with high
high thicknesses and with a wide spectral sensitivity range from the red to the blue region. As a result, high
diffraction efficiency with excellent sensitivity can be obtained with the right choice of the monomers. Here we
will present recent results with PVA-acrylamide composition. One of the drawbacks of the photopolymers is
its thermomechanical stability, for this reason, sol-gel materials, a mixture of organic-inorganic material, have
been recently developed. In this review we will present the experimental results in transmission and reflection
holograms.
In this paper we have studied the recording of Fourier holograms in a PVA-AA photopolymer, analysing the influence of beam ratio in the quality of the reconstructed images. As a result, it has been observed that the variation of the beam ratio produces significant changes in the response of the material, showing that there is a range of optimal values that gives the best performance of the photopolymer for the recording of Fourier holograms. Effects on edge enhancement as consequence of spatial filtering on the reconstruction stage has been observed for low values of beam ratio. The best beam ratio obtained from this study has been used for holographic multiplexing of four Fourier holograms.
In recent years the interest shown in dry photopolymer films as holographic recording materials have increased dramatically. The main reasons for this are the special properties of these media, such as high diffraction efficiency, low noise, real-time processing and low cost. Moreover, these materials are an important option for displays, high density data storage, micro-optical elements and other information processing applications. In these materials the hologram formation mechanism has been broadly studied, and it has been proposed that the temporal behavior of the diffracted beams depends mainly on the diffusion processes. Thus, the spatial modulation of the refractive index and its evolution over time is the result of non-uniform polymerization and the diffusion of monomers. In this work an analysis of the proposed models and the effect of the diffusion coefficient on the behavior of polyvinylalcohol-acrylamide-based compositions is realized.
We present the results obtained using two different types of the new panchromatic ultra-fine grain emulsion BBVPan, manufactured by Colourholographics Ltd. The first emulsion type was manufactured by mixing three monochromatic precipitates, so that each silver halide grain is sensitised with one dye only. The second emulsion was obtained by making one single precipitate containing all three dyes mixed together, so that each silver halide grain may be sensitised by the three dyes. Both emulsions have been compared in order to produce multiple band holographic reflection gratings, multiplexed on a single layer of material. Three different laser systems were used: He-Cd (442 nm), frequency-doubled Nd-YAG (532 nm) and He-Ne (632.8 nm). High diffraction efficiencies, of over 52\%, were obtained for each of the three bands, with little wavelength shifting. Tests with diffuse objects have been also carried out, studying colour balance for each of the emulsions.
Holographic techniques have been used for manufacturing multiple band one-dimensional, two-dimensional, and three-dimensional photonic crystals with different configurations, by multiplexing reflection and transmission setups on a single layer of holographic material. The recording material used for storage is an ultra fine grain silver halide emulsion, with an average grain size around 20 nm. The results are a set of photonic crystals with the one-dimensional, two-dimensional, and three-dimensional index modulation structure consisting of silver halide particles embedded in the gelatin layer of the emulsion. The characterisation of the fabricated photonic crystals by measuring their transmission band structures has been done and compared with theoretical calculations.
In this work we have studied the characteristics of reflection gratings recorded with BB640 emulsions from Colourholographics Ltd. processed with a set of different developers and bleaching techniques. Overall diffraction efficiencies evaluated with spectral response curves result in values higher than 70% (80% taking into account reflection losses) for conventional fixation free rehalogenating bleaching processes, with very low scattering.
A slightly lower value was obtained with reversal bleaching techniques, but with lower scattering in the recordings.
For the latter, an analytical analysis of the spectral responses based on the Kogelnik's theory has been performed, leading to anomalous results regarding physical thickness of the hologram and the reply wavelength, a performance that points towards holographic profile distortions. We have also used a completely different processing scheme based on Kodak D8, a developer never used in reflection holography, with a direct bleach rendering 40% diffraction efficiency, a broad bandwidth and a reconstruction wavelength longer than the recording one.
Ion this work we present a distortion of the usual H-D curve due to the action of a high contrast developer, Kodak D8 on ultra fine grain emulsion. This effect has been found for emulsions BB640, with a mean grain size of 20 nm. This anomalous curve shows two different linear zones for two different exposure ranges and no solarization region. Densities higher than 11 have been measured. Superaditivity effects of D8 with different developing agents were studied. Based on obtained result with different holographic bleaching processes, some ideas on the mechanisms involved in the anomaly have been proposed.
Two wave-mixing (TWM) is reported for an acrylamide based photopolymer at a wavelength of 633 nm where the material absorbs light. Measurements of diffraction efficiency where also made at 441. In TWM experiment, transfer of energy from the reference beam to the object beam is showed and the mechanism of the image formation is studied using real time measurements.
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.
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.
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.
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.
Photopolymers have been analyzed as holographic recording materials by measuring their diffraction efficiency in relation to the index modulation that is obtained with these materials, their spatial response and their energetic and spectral sensitivities. However, even though they are considered good recording materials for the storage of information and for the production of holographic optical elements, little information has been offered on the image quality that these recording materials produce. Among the different sources of noise in holography, noise gratings have been analyzed extensively in photographic emulsion due to the granular nature of these recording materials. However, information about photopolymers is quite scare. For material that work in real time, it is the transmittance function which measures the appearance of noise gratings given that the presence of this noise source manifests itself when transmitted light decreases due to diffraction. We present a theoretical model that relates the photopolymer transmittance function response with the noise grating structure. In keeping with the experiments we can say that noise gratings also appear in photopolymers which proves the presence of a certain granular structure in these materials. Their appearance and storage in these materials can be used as a methodology for the optimization of these recording materials.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.