Fabrication process of arsenic-sulfide (As-S) and arsenic-selenide (As-Se) optical fibers has been improved to enhance the transmission in the mid-IR region. Typical attenuation spectrum of As-S or As-Se optical fibers shows impurities bands, such as S-H, Se-H, O-H, which limit their operation and cause the increase of the attenuation loss in the mid-IR. Precursors purification methods and glass processing were improved to minimise those impurities bands. Regarding As- S fibers, the attenuation around 2.7 μm is 0.12 dB/m and S-H concentration is lower than 0.3 ppm. In the case of As-Se fibers, the minimum of attenuation located at 6 μm is 0.2 dB/m and Se-H concentration is lower than 0.5 ppm. Efforts have been also made to improve the mechanical properties which are usually affected by several parameters such as drawing conditions or heterogeneous inclusions contained in the glass. The double-crucible method gives high quality core/clad interface and consequently increases the strength of the fiber. Inclusions consist mainly of carbon and silica particles. Those impurities enter the glass from initial precursors and are also formed by interaction with the apparatus material. Thanks to the process improvement, impurities particles are minimized and tensile strengths up to 0.32 GPa and 0.41 GPa are reached for As-Se and As-S fibers respectively.
Multimode PMMA optical fibres with a cladding made from ion-selective membrane were designed, prepared, and
investigated. Some were prepared by direct drawing of membrane-coated preforms and others were overcoated. Results
obtained indicate loss of membrane sensitivity that is attributed to decrease of its ionic permeability. Absorbance of the
fibre follows a modified Beer law as confirmed by rank analysis of series of spectra and explained by significant mode
coupling within the fibre.
We present current work developed at INO on phosphate glass optical fiber for laser and amplifier applications at 1.54
microns. Core and cladding glasses were fabricated by a multi-components melting process which gave an uniform
refractive index core profile. Rod-in-tube method under Argon atmosphere was used to fabricate optical fibers. The
effect of nitrogen atmosphere on hydroxyl groups OH- during glass melting was studied. The absorption coefficient
calculated at 3.42 μm was found to be lower than 0.5 cm-1 which corresponds to less than 70 ppm OH-. Absorption and
emission cross sections were calculated at 1534 nm. Fabrication process allowed us to decrease background losses of
core Er3+ - Yb3+ co-doped fiber between 0.02 and 0.04 dB/cm. Laser power was measured at 1563 nm and a 26% slope
efficiency was achieved with a 22 cm-long single-clad fiber co-doped with 1.1 wt% in Er3+ and 11.1 wt% in Yb3+. For
the same fiber, an internal gain was found to be 20 dB at 1536 nm for a 5-cm-long fiber.
The reversible reaction that takes place in the writable, readable, erasable (WRE) photosensitive materials involving fulgides (ABERCHROM 540 and 670) was investigated with a photochemical and holographic approach. It appeared that the fatigue of the photosensitive material was strongly dependent on the properties of the matrix used as a support. This was precisely established both by spectroscopic monitoring (λmax, absorbancemax, photo-stationary state) and by following the diffraction efficiency η values. There was a nice correlation between the evolution of the spectral features of C isomer and of the η values all along the WRE cycles. This combined approach was applied to four different supports: PVK, PMMA, PEPC/PS and epoxy RESIN. So for both fulgides: (1) PVK, frequently used in optics, appears as being the worst one. The starting fulgides were destroyed after only a few WRE cycles. This was assigned to the intrinsic photoaging of PVK whose absorption in UV domain is far from negligible and leads to the formation of radical species able to attack the fulgide. (2) Holograms recorded in PMMA and PEPC/PS present similar behavior with a loss of ≈10% after 8 cycles. (3) Epoxy RESIN appears to be a very good candidate for these reversible systems; no fatigue was observed after 40 cycles. It has to be attributed to the matrix in which the detrimental rotation process, giving rise to the non photochromic Z isomer, is strongly inhibited.
Dynamic holographic recording was performed on two fulgides (A540 and A670)/Doped films. Maximum diffraction efficiency of 7% and 6% has been achieved on A540 and A670 doped PEPC/PS films. The effects of the matrix, writing intensity and film thickness on diffraction efficiency were studied. Holographic fatigue resistance in polymer matrix and epoxy resin has been investigated. It was found that holographic fatigue of fulgide doped in epoxy resin is closed to zero at least after 40 Write-Read-Erase cycles (WRE).
We report a photosensitive composite structure consisting of chalcogenide glassy semiconductors and copolymeric thermoplastic materials. Our researches were aimed to find out new approaches of using photothermoplastic materials. (PTPM) as two-layered media for holographic and optical data recording. This approach was based on creating the modified PTPM structures with enhanced characteristics as well as on performing the new processes of recording onto PTPM. Some modifications in the recording procedure and equipment setup were carried out. It is established that PTPM systems based on donor-acceptor layers have a photosensitivity of 10-3 to 10-4 J/cm2. The introduction into them an additive of photochromic dye increases the photosensitivity of donor-acceptor systems by 2 - 3 times. The essential growth in photosensitivity is observed in the blue-to-green range of spectrum. A method of photothermoplastic recording of holograms on a PTPM with a photosensitive layer of chalcogenide glassy semiconductors is proposed. Storing the whole data file of holograms followed by their development does the recording of optical information.
Currently organic photochromic compounds have been considered as materials of growing importance for use in optical memory applications. They have been characterized by a set of unique characteristics, and could be easily fabricated in different formats and at low-cost. We studied a new class of photochromic composites consisting of carbazole-contained polymeric hosts with spiropyran-substituted dyes. These composites have been synthesized and experimentally characterized as holographic material for direct high-resolution holographic recording in whole visible spectra. We concluded some general principles of photochromic media design for achievement of high sensitivity and diffraction efficiency while hologram records.
Photochemical characterization and holographic recording of fulgide Aberchrome 670 and 540-doped polymethyl methacrylate (PMMA) were investigated. Upon UV and visible exposure, closed-form absorbency followed first-order kinetic. The real time holographic recording in fulgides doped PMMA films were studied. The effect of dye concentration, thickness of the film and the recording intensity on diffraction efficiency was reported. We used the Langmuir-Blodgett (LB) technique in order to transferring a compact multilayer of fulgide spread on water surface between two thin films of cellulose acetate (CA). The preliminary results of the surface pressure-area isotherms obtained by LB show the transfer of the fulgide between two CA thin films. Finally, the photochromic reaction of fulgide in LB films was investigated.
We report a new photochromic composite polymer consisting of poly-N-epoxypropylcarbazole (PEPC) polymeric matrix with a nitro-brome-substituted spiropyran (BNSP) photochromic dye. The PEPC + BNSP films can be considered as negative photochromic recording media. They are colored in the initial state and bleached upon irradiation within the visible spectra. When we placed the bleached samples to the darkness, they slowly revert to the colored form. This process has strong temperature dependence, so one can either 'freeze'' or accelerate changing of the current coloration state in the PEPC + BNSP. The experimental measurements are evaluated in conjunction with its potential applications for optical holographic recording in the visible spectral range. The real-time holographic recording procedure in PEPC + BNSP films was studied. The diffraction efficiency values reached the maximum of 23 percent at spatial frequency of 1600 line pairs per mm, during direct hologram recording with the 532 nm Coherent VERDI laser irradiation. Light exposures were ranged from 70 to 280 mJ/cm2. The investigated compounds have good perspectives for use in holography, two-photon optical data storage, electro-optics, and optical-limiting applications due to coupling of some unique properties such as high optical non-linearity, well charge transport, short response times, no-limiting resolution ability, etc.
By means of real-time holographic recording, two important classes of photochromic compounds (spiropyrans and
fulgides) have been characterized. For spiropyran molecules, important thickness and writing intensity effects were
observed.
Concerning fulgides molecules, photochemical fatigue resistance in different polymer hosts was investigated. After 10
irradiation cycles, the closed form lost 9, 1 1 , 13 and 35% of its initial absorbance respectively in PS, CA, PMMA and
PVK. For the holographic study, diffraction efficiency in fulgide doped PMMA films was strongly dependent on the
writing intensity: the rise time 'r takes values 25and 7s for respectively 2 and 8 mW/cm2. Optimum fulgide concentration
and writing exposure have been obtained: diffraction efficiency is maximum with a concentration of 2% and an intensity
of 4mW/cm2.
Keywords:Photochromism, photosensitive materials, fulgides, spiropyrans, polymethylmetacrylate, polyvinylcarbazole,
real-time spectrometry, photochemical fatigue resistance, holographic recording.
A comparative investigation of the photochemical behavior of dichromated gelatin
(DCG), dichromated polyacrylic acid (DCPAA) and dichromated polyvinylalcohol (DCPVA)
gives evidence for the similarity of the photochemical behaviour involved when recording
holograms in DCG and DCPVA. Chromium (V), the chromium species resulting from the
photoredox process between the starting chromium (VI) (dichromate) and the polymeric
chain, is stable, likely strongly complexed in gelatin and polyvinylalcohol. The quantum
yields of the reaction are high and similar for both reactions. On the contrary, even though
chromium (V) is also formed during the primary process in DCPAA, this species is quite
unstable and disappears as soon s the irradiation is stopped. The behavior observed in DCG
can be assigned to the presence of CM groups on the polymeric chain, these groups being the
only groups present in polyvinylalcohol.
The photoinduced reversible color change and in-situ recording of fulgide Aberchrome 670 doped polymethyl methacrylate (PMMA), cellulose acetate (CA) and polystyrene (PS) were investigated. Upon UV and visible exposure, closed-form absorbency followed first-order kinetic. The rate constants KUV and KVIS for respectively the coloring and bleaching process were determined. In PMMA matrix KUV equals 1.2 * 10-3 s-1 and KVIS equals 11.1 8 10-3 s-1, in CA matrix kUV equals 2.7 * 10-3 s-1 and kVIS equals 6.4 8 10-3 s-1 and in the case of PS film kUV equals 2.1 * 10-3 s-1 and kVIS equals 11.9 * 10-3 s-1 were obtained. These results show that, KVIS is much larger than KUV for all matrices. Photochemical fatigue resistance in different polymer matrices was investigated. We found a loss of 9, 11 and 13 percent in PS, CA and PMMA respectively, after 10 repeated UV and visible cycles. The real time holographic recording in fulgide doped PMMA films were studied. We have analyzed the effect of the photochromic concentration, the thickness of the film and the recording intensity on the diffraction efficiency. The highest diffraction efficiency is obtained for the concentration of 5 percent of the fulgide dye in PMMA film with an exposure energy of 10 mw/cm2. For the same sample we have not observed any diffraction beam when the sample was illuminated by an intensity of 3 mw/cm2.
Photochromism and real-time holographic recording were characterized for two principal classes of photochromic compounds: spiropyrans and fulgides. For spiropyran molecules, important thickness and writing intensity effects were observed. Concerning fulgide, in PMMA matrix, the closed form presents a maximum of absorption centered at 525 nm upon irradiation at 365 nm. We have determined the photoreaction rate constants kUV and kvis respectively for the coloring and bleaching process: kUV equals 1.2 X 10-3 s-1 and kVIS equals 11.1 X 10-3 s-1. Photochemical fatigue resistance in different polymer matrices was investigated. We found a loss of 9, 11, 13 and 35 percent respectively in PS, CA, PMMA and PVK. Concerning holographic recording, we obtained diffraction efficiency (eta) equals 0.65 percent in PMMA films 30 micrometers thick.
The photoinduced reversible color change in photochromic doped PMMA and PVK films was investigated. Upon UV and visible irradiation, closed form absorbency, in the beginning of the photoreactions, followed first-order kinetic and, then deviated from this order. The rate- constants kuv of the coloring process, and kvis of the bleaching process, were determinated. For the two diarylethenes studied, kuv is much larger in both polymer matrices. However, kvis is stronger in PVK for fulgide Aberchrome 670. Both rates are identical in PMMA. Photochemical fatigue resistance was studied. For fulgide Aberchrome 670 in PMMA matrix, we found 13 percent disappearance after 10 repeated UV and visible cycles.
We have been working on dichromated photosensitive materials for several years. After investigating the photochemical process in various systems, it appears that the chemical structure of the polymeric matrix plays an essential role in the progress of the reaction that takes place upon irradiation by the laser beams. If the primary photochemical process is always the electron transfer from the matrix to the metallic cation giving rise to chromium (V) and a macroradical, the fate of chromium (V) in the system strongly depends on the chemical structure of the polymer. In dichromated poly(acrylic acid) DCPAA, chromium (V) is an unstable species only detectably by ESR spectroscopy upon irradiation: it disappears after stopping the irradiation very fast. On the contrary, chromium (V) is surprisingly stable in poly(vinyl alcohol) and in gelatin. The first spectral evolution corresponds to the only reduction of chromium (VI) into chromium (V) as evidenced by the presence of an isosbestic point. The subsequent reduction of chromium (V) is a very slow process: the complete transformation into chromium (III) is only achieved after several days. As a result, we were able to estimate the UV-visible spectrum of chromium (V) in the matrix and for the first time, it was possible to quantitatively follow the formation of this species and to draw some conclusion about the complexation sites in gelatin.
The photochemical behavior of dichromated gelatin and of different aminoacids-chromium (VI) systems was investigated. The photoredox process that takes place between chromium (VI) (complexed or not) and the organic moiety leads to the formation of chromium (V) which is then reduced to chromium (III) likely complexed in the medium. In chromium (VI)-aminoacids systems, the quantum yield (Phi) , that measures the efficiency of a photon at a given wavelength, strongly depends on the reductive properties of the aminoacid. (Phi) is proportional to aminoacid concentration. In irradiated DCG films, the formation of chromium (V) is observed and this intermediate species appears to be surprisingly stable in the polymeric matrix. For the first time, we were able to quantitatively measure the formation of Chromium (V) in dichromated photosensitive 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.