Carbazol-containing polymers were shown to be good reliefographic photosensitive substrates for holographic
registration. Holographic images with satisfactory properties were obtained with carbazolic copolymers containing
carbazolylethylmethacrylate and octylmethacrylate units and iodoform as sensitizer. The final goal of this study is to find
the best copolymer formulation ensuring large amount of data stored with a high transfer rate and an optimized lifetime
of the hologram and of the host polymer. It is then crucial to elucidate the involved photochemical mechanisms. We first
carried out irradiations at 405 nm (wavelength of the laser diode used for holographic recording) in order to follow the
photostructuration of the doped polymer. Spectroscopic analyses showed that the formation of a charge transfer complex
is observed and its increase of concentration in the polymer could be followed versus exposure time. We also focused
our attention on the durability of the hologram and of the polymeric matrix itself. Under irradiations representative of
natural ageing (λ>300 nm), we have shown that the complex is successively formed and destroyed and that the
photodegradation of the polymer matrix was also observed.
Agar is a natural polysaccharide which, when doped with dichromate ammonium, can be considered as a promising
light sensitive material used for real time hologram recording. The volume transmission gratings were recorded with a
Kypton laser at 413 nm and they were read in real-time with a He/Ne laser at 632.8 nm contrary to dichromated gelatin.
The so obtained holograms formed were phase holograms due to a refraction index modulation. The optimisation of
chemical and physical parameters was investigated in order to form high quality holograms. It was demonstrated the
crucial role played by the remaining water in the final film on the value of the diffraction efficiency. In the optimal
conditions, a maximum diffraction efficiency of 37 % was attained. Both on-off experiments and the storage of the
exposed materials at room temperature and in the dark reveal that the holograms were stable. An attempt to rationalize
the set of results in terms of chemical structure of the polymeric matrix and of its ability to stabilize chromium (V) is
presented.
A comparative investigation of the photochemical behavior of dichromated gelatin (DCG), dichromated polyacrylic acid (DCPAA) and dichromated polyvinylalcohol (DCPVA) gave 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, was stable likely strongly complexed in gelatine and polyvinylalcohol. The quantum yields of the reaction are high and similar for both reactions. On the contrary, even though chromium (V) was also formed during the primary process in DCPAA, this species was quite unstable and disappeared as soon as the irradiation was stopped. The behavior observed in DCG can be assigned to the presence of OH groups on the polymeric chain, these groups being the only groups present in polyvinylalcohol. Actually, the stability and the state of complexation of the different chromium species was completely opposite in the two matrices: the stabilization of chromium (V) resulting from the photochemical charge transfer in DCPVA, by complexation with PVA is in contrast to what was observed in DCPAA where chromium (V) was highly instable. Regarding chromium (III), the final reduction chromium species, it was complexed in PAA and not in PVA. The experiments performed on films of DC (PVA+PAA) with only a few percents of PAA gave evidence for the strong influence of the presence of the carboxylic groups on the photochemical behavior: the rate of the formation and the
stability of chromium species that reflects the chelating properties of the polymeric matrix. The photochemical results were correlated to the results obtained when recording holograms in the corresponding material: a very nice agreement appeared between the two sets of results. An innovative approach combining the monitoring of the structural modification of the polymeric matrix and the fate of the various chromium species ((VI), (V) and (III)) was then implemented. For the first time, it was established that chromium (V) was at the origin of the cross-linking implied in the hologram formation by acting as a bridge between hydroxyl groups of the polymeric chains. A second unanswered question was also elucidated. The improvement brought by ammonium dichromate with respect to potassium dichromate involves amide groups as additional chelating sites for chromium (V) resulting in the increase of the matrix cross-linking.
The photochemical behavior of dichromated polyvinylalcohol (DCPVA) films was analysed upon exposure at 365 nm in connection with the hologram quality recorded in such a photosensitive material. The evolution of both involved species, chromium and polyvinylalcohol, were quantified by implementing an innovative approach. This approach combines the monitoring of the structural modification of the polymeric matrix and the fate of the various chromium species ((VI), (V) and (III)). For the first time, it was established that chromium (V) was at the origin of the cross-linking implied in the hologram formation by acting as a bridge between hydroxyl groups of the polymeric chains. A second unanswered question was also elucidated. The improvement brought by ammonium dichromate with respect to potassium dichromate involves amide groups as additional chelating sites for chromium (V) resulting in the increase of the matrix cross-linking.
Irradiation of dichromated polyvinyl alcohol and dichromated polyacrylic acid DC(PVA-PAA) at 365 nm was
investigated in order to understand the involvement of the polymeric matrix in the reduction process of the Cr(VI)
leading to the formation of the hologram. The photochemical evolution of the matrix was directly correlated to the
disappearance of the absorbing species, chromium(VI). A special attention was paid to the absorption profile of the
films. Due to the impermeability of the polymer, no oxidation proceeded. The reduction of Cr(VI) into Cr(V) induced the
formation of carboxylate species perfectly correlated with the consumption of carboxylic groups. Besides the acido-basic
reaction undergone by the carboxylic groups, the reduction of Cr(VI) provoked the cross-linking of the polymer. Each
polymer appears to play a specific role in the mechanism.
The holographic properties of mixed dichromated [polyvinylalcohol (PVA)/polyacrylic acid (PAA)] were investigated and compared to the pure photosensitive materials DCPVA and DCPAA. It appeared that the addition of 25% in weight of PVA in PAA strongly increase the diffraction efficiency (DE) of the resulting hologram. On the contrary, the addition of PAA in PVA only slightly increases DE values. In the last case, the addition of a complexing agent such as dimethylformamide DMF improves the hologram quality.
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).
Gelatin (G) can be described as a peptidic chain with different pendent groups among which, hydroxy groups-OH, carboxylic groups-COOH and amino groups -NH2. Works performed on polyacrylic acid (PAA), a poymeric chain with only pendent-COOH group and on polyvinyl alcohol (PVA) with only -OH group revelaed the strong influence of the nature of the chemical structure on the photochemical behavior of dichromated photopolymers, DCG, DCPAA and DCPVA. Actually, the stability and the state of complexation of the different chromium species was completely opposite in the two matrices: the stabilization of chromium (V) resulting from the photochemical charge transfer in DCPVA, by complexation with PVA is in contrast to what was observed in DCPAA where chromium (V) was highly instable. Regarding chromium (III), the final reduction chromium species, it is complexed in PAA and not in PVA. The primary proces is identical in DCG and in DCPVA, so PVA appears as a good model of the first step of gelatin behavior. But the material obtained after irradiation and treatment of DCG only contains chromium strongly complexed by gelatin. The experiments performed on films of DC with only a few percents of PAA gave evidence for the strong influence of the presence of the carboxylic groups on the photochemical behavior: the rate of the formation and the stability of chromium species, mainly chromium (V), involved in the process. Chromium (V) appears to play a key role in the photosensitive properties of dichromated materials. The diffraction efficiencies of holograms recorded in DCPAA or DCPVA resemble the profiles of chromium (V) evolution.
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.
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.
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.
Dichromated polyacrylic acid (DCPAA) and dichromated polyvinylalcohol (DCPVA) have been investigated with a double approach: photochemical behavior and holographic results. The study focused on two particular systems: the effect of the addition of nitrilotriacetic acid (NTA) or dimethylformamide to the photosensitive material. From the photochemical mechanism it was possible to assess that the complexing ability of both compounds plays a major role in the optimization of the holographic properties of the material. On the contrary, the presence of an electron donor like NTA in DCPAA is less favorable. A close correlation seems to be present between the photochemical behavior and the results obtained in holography.
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.
Dichromated poly(acrylic acid) (DCPAA) films have been investigated as photopolymer recording material. Thin DCPAA films with dimethylformamide have been used to photofabricate surface relief groups. The formation of these gratings depends on the self-development time in darkness subsequent to the illumination at the wavelength of 442 nm and is obtained without any chemical treatment or wet processing. In this experimental investigation, the effect of light exposure, heat treatment, and pH solution on the holographic characteristics of these gratings is studied.
Photocrosslinkable recording materials are used for long time as one of the best materials to fabricate diffractive optical elements and holographic optics. Dichromated gelatin is the most widely used materials for those applications. Research was done for replacing the dichromated gelatin by some metal doped polymers. We will make a review of materials and applications as well as some results regarding the photophysics and photochemistry of metal doped systems.
Diffraction properties of phase relief gratings which can be photofabricated in dichromated poly(acrylic acid) films have been analyzed. The formation of these gratings which produce multiple diffracted waves takes place in darkness subsequent to the holographic illumination at a wavelength of 442 nm. The holographic surface relief gratings are obtained by self-development and without any chemical treatment or wet processing. Theoretical calculations of diffraction efficiencies and experimental results at a wavelength of 543.5 nm for a seven beam splitter are presented.
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.
Photoinduced holographic surface relief gratings have been fabricate din dichromated poly(acrylic acid) films. These gratings are formed in darkness subsequent to the illumination at 442 nm and they are obtained without any chemical treatment or wet processing. The influence of chemical parameters, such as ammonium dichromate and dimethylformamide concentrations, on the holographic characteristics of these gratings have been investigated. Holographic characteristics of the recording medium such as diffraction efficiency as a function of exposure, ammonium dichromate and dimethylformamide concentrations, and spatial frequency are presented in this paper.
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.
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.
Dichromated poly(acrylic acid) (DCPAA) films with dimethyl formamide (DMF) have ben sued to photofabricate surface relief gratings. The formation of those gratings depends on the self-development time in darkness subsequent to the illumination at a wavelength of 442 nm and is obtained without any chemical treatment or wet processing. The modulation depth of those holographic surface relief gratings and the spatial frequency response of the thin DCPAA-DMF films have been chosen to characterize that self- developing photopolymer system. Those holographic characteristics are presented in this paper.
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 to 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.
Dichromated poly(acrylic acid) films with dimethyl formamide have been investigated as UV photosensitive recording medium for the fabrication of diffractive optical elements. Surface relief structures with large depth modulation have ben formed on these films. Relief depth of surface gratings as a function of exposure time and the spatial frequency of the gratings are presented. Atomic force microscopy 3D views of surface relief gratings are also presented.
Dichromated polyacrylic acid (DCPAA) has been used as real time holographic recording material. We report here the photochemical behavior of DCPAA when irradiated under conditions similar to those used for hologram recording. A photoredox process was observed whose efficiency depends on the presence of an electron donor, dimethylformamide (DMF). By ESR spectroscopy upon irradiation four different species were detected and identified: (1) chromium (V) of thermal origin (in the dark); (2) chromium (V) of photochemical origin; (3) an organic macroradical; (4) chromium (III). DMF appeared to possess a strong influence on the formation of these species.
Metal doped polymers are used as holographic recording material in which the first step is the absorption of the light by the metallic center. The primary mechanism, in most cases an electron transfer in the excited state, is tentatively described for polymeric material doped with chromium(VI) and iron(III).
Dichromated poly(vinyl alcohol)-xanthene dye (DCPVA-XD) systems have been employed as real-time holographic recording materials. In this paper, holographic characterization of dichromated poly(vinyl alcohol) with fluorescein (Fl), eosin Y (EY) and Rose Bengal (RB) is presented. In addition, a systematic ESR spectroscopic investigation was also performed on these systems. The photochemical evolution of Cr(V), Cr(III), polymer radical and dye radical in these systems has been monitored and a comparison is made.
The photoredox process occurring between HCrO4- and a vinyl monomer (acrylamide or acrylonitrile) leads to the formation of chromium(III) and the polymer as final photoproducts. The primary process is a charge transfer between HCrO4- in the excited state and the monomer giving rise to chromium(V) and to an organic radical initiator of the polymerization. The influence of pH, monomer concentration, absorbed light intensity Ia and chromium(VI) concentration on the polymerization rate Rp are reported. Two different domains are detected as a function of chromium(VI) concentration: at low concentration, the process of chain termination occurs by mutual annihilation of the macroradicals whereas at high concentration a process of oxidative termination of the radicals by chromium(VI) is involved. The influence of copper(II) on these different processes is also described.
Dichromated Poly(vinyl alcohol) films with and without dyes and electron donor have been employed for real-time holographic recording and for the fabrication of holographic optical elements (HOEs). The primary photoprocess of the interaction of Cr(VI) with the polymer has been followed under various experimental conditions through esr spectroscopy. The effect of the pH of the coating solution, concentration of dichromate, electron donor and dyes on the evolution of intermediates has been discussed. A suitable mechanism involving the electron transfer from the polymer to Cr(VI) leading to the formation of Cr(V) and polymer radical, which further undergoes reaction to produce Cr(III) and crosslinked polymer matrix, has been suggested.
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.