We present our first experimental results of lens irradiation obtained with ultrashort pulse lasers. The irradiation was done with the Ti:Safire laser which irradiates at 800 nm with a repetition rate of 76 MHz. The maximum average intensity used was 300mW, with pulses of 4 nJ. The holographic images obtained have given us information about the focusing process of the lens capsule as well as its rupture, thus indicating the level of penetration in the lens and capsule rupture. The results obtained in these first experiments allow us to establish protocols and techniques to break the capsule of the lenses as well as to carry out possible modifications inside the lens. As the optical system developed works in real time, it is possible to perform dosimetry measurements in the light-lens interaction processes giving quantitative information about the breakdown of the tissue structures. In future projects the possible side effects of thermal action and local modification of the capsule will be analyzed; these are important aspects in the field of noninvasive lens surgery.
Digital Holographic Microscopy (DHM) is a potentially non-invasive new technology which can be applied in many
areas from applied imaging science to biomedical optics. DHM is an interferometric technique that gives us a number of
important advantages such as the possibility to acquire holograms at high speed, to obtain complete information about
amplitude and phase and to use image processing techniques. In this sense, DHM offers rapid 3D imaging with a
theoretically higher resolution than OCT (Optical Coherent Tomography). By this technique optical path measurements
with sensitivities in the nanometer range of reflective and transparent objects can be obtained.
In this work, we use DHM to study the effect of ablation using 4.5 nJ pulses on chicken corneas. For this, a titanium
sapphire laser at 800 nm and 76 MHz frequency (Vitesse, Coherent Inc. USA) was focused to its diffraction-limited spot
size by a 10x objective of 0.3 numerical aperture. The width of the pulse (170 fs) at the sample was measured by spectral
techniques. The average beam power at the sample was 340 mW and all the system was mechanically driven by a XY
synchronization unit that controls the speed of the sample movement. The speed of the sample was varied between 1-50
μm/s.
The studied chicken corneal tissue was previously processed by Trypan dye in order to visualize the irradiated area. The
photodisrupted zone was analyzed by a HDM technique by illuminating it using a laser diode source (λ=683 nm) linearly
polarized in a modified Mach-Zehnder with an off-axis geometry configuration. The reflected object wave by the tissue
surface (specimen) interferes with the reference wave and a CCD camera records the hologram. As a result, the influence
of the speed of photodisruption in the depth of the ablated corneas was analyzed. Therefore, it is possible to analyze
thermal and photoirradiated effects on corneal tissues which allow us the possibility to optimize the interaction of
intratissue and the intratissue target region of interest.
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.
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.
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.
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.
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