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Photonics West_2002

Holographic Materials VIII,

Monday 21 January

Hilton Hotel:Almaden Room II3:30 pm

Report 4659-59

Selfdeveloping dichromated gelatin thick layers:

manufacturing and control

Alexander Malova, Nadya Reinhandb, Yury Vigovskyc, Yulia Zagainovaa, Serge Malovd, Igor Bogdand, Irina Semenovae

aIrkutsk State University, Gagarin bul., 20, Irkutsk, 664003, Russia

bInstitute of Mechanical Engineering Problems of the Russian Academy of Sciences,

V.O., Bolshoi pr., 61, St.Petersburg, 199178, Russia

cMeDia Ltd., Novoslobodskaja str. No 31/1, Moscow, 103055, Russia

dLaser Physics Institute of the Siberian Branch Russian Academy of Science, Irkutsk Office,

a/ya 4038, Irkutsk, 664033, Russia

e A.F.Ioffe Physical Technical Institute of the Russian Academy of Sciences,

Politechnicheskaya, 26, St.Petersburg, 194021, Russia

e-mail: malov@physdep.isu.ru

The work was supported by Russian Basic Researches Fond project No 01-02-17141 and European Office of Aerospace Development (USA) project No 2057P.

2002 is the 150-years anivessary of the Talbots discovery of the dichromated gelatin light sensitivity.

In 1968, Shankoff proposed to record hologram using layers of dichromated gelatin (DG) and demonstrated the possibility to produce highly efficient DG holograms through the stage of fast dehydration of a recording layer with propanol. Dichromated gelatin is a practically ideal phase holographic recording material, which makes it possible to approach the theoretical limiting value of the DE and to record more than 1000 superimposed holograms. However, the low photosensitivity of DG photomaterials as compared with silver-halide photoemulsions and the low reproducibility of the results of recording with DG holograms restrict applications of DG media to predominantly the replicating and printing of holograms and diffraction optical elements. Record magnitudes of phase modulation of a relief image, high transmittance, ultralow noise level, and a high resolution that can be achieved with DG layers still keep DG in the row of materials that hold much promise for recording image holograms.

In the middle 1970th Nakashimura, Inagaki and Nishimura are improved the processing of hardened DG by adding a treatment with hydrochloric acid aqueous solution. The HCl processing yelds to the light sensitivity ten times greater than that obtained by the Shankoff-method. Namely, a processing of hardened DG is improved by increasing the dissolution power of a gelatin layer in diluted hydrochloric acid solution, and, as a result, holograms obtain high light sensitivity and high reproducibility. Holograms treated with HCl processing are recorded in the non-linear exposure region of diffraction efficiency and only on the high hardened gelatin layer.

In 1970, Erko and I used the HCl processing for investigation of the recording mechanism in DG layers. For it the hologram in the unhardened DG was treatment with HCl-bath and long time washing in the warm water and vacuum dehidratation of DG layer. The result was the next- fig. 1.

 

Fig. 1. Hologram recording in DG layer.

The latent holographic image DE at spatial frequency equal to 5 lines per mm,

The phase relief of the same hologram on the 0,63 mkm wavelight.

The recording wavelength was the 0,44 mkm.

Fig. 2. The relief parameters of the recording gratings dependce on the recording light intensity for 0,44 mkm wavelength.

1 the exposure nedeed for the phase relief equal to D j =p /3 rad dependence on the recording light intensity (0=mJ/cm2 ; I0=0,5 mW/cm2);

2 the phase relief value for =10 mJ/cm2 divided to maximal phase relief value in dependence on the recording light intensity;

3 the exposure energy for the maximum phase relief dependence on the recording light intensity.

 

The primary photochemical reaction is two channel process, and the each channel is connected with different valency degree of the chromium ions. The relations between this channel is dependce on the spatial frequency and the recording light intensity. After developing process the phase relief has the two maxima form.

 

Fig . 3. Hologram recording in DG layers for 1940 lines per mm.

the latent image DE at spatial frequency equal to 1940 lines per mm;

the DE dependce on the intensity of the first order of the diffraction on the latent image for the testing wavelenght 0,63 mkm: 1 the exposure energy is less than nessesery for the maximum DE of the latent image; 2 - the exposure energy is more than nessesery for the maximum DE of the latent image.

For the high DE hologram recording the best regim is to exposure only up to first maximum for latent image. The DE of the DG holograms depends on the light recording intensity, too/

 

Fig. 4. The hot water vapour development of the DG layer.

h - the diffraction efficiency of the holographic gratings recorded at 0,44 mkm wavelength and spatial frequency 50 lines per mm.

(0-t1 ) the recording process up to h =0,02%.

(t1 -t2 ) the vapour development process up to h max.

(t>t4) the second (postprocessing) vapour develop.

The recording intensity was near 1mW/cm2.

The amplification of a latent holographic image in DG may be achived by means of the hot water vapour development. In this case vapour development leads to modulation of a surface relief (layer thickness is changed) but not to variation of refractive index inside the layer. This circumstancees limits the maximal spatial frequency recorded on the layer by a value of 300 lines per mm. The vapour developing process has the good reproducibility and may be used for a real-time testing of DG layers for holography.

The main distinguishing feature of DG as a polymer is associated with the natural origin of gelatin, which is produced as a result of the denaturation of a collagen whose macromolecules have a structure of a triple hyperhelix (fig. 5). Therefore, the native state of a gelatin macromolecule also has a biohelix-like structure, which makes n possible to prepare DG layers with an initially ordered (helical) molecular structure. In the process of development, a phase transition from the ordered (quasi-crystalline) state to a disordered (quasi-amorphous) state occurs under the action of light and water at all the levels of structure organization of a gelatin layer, which leads to large photoinduced changes in optical characteristics of a DG layer.

 

 

Fig. 5. Transformation of collagen into gelatin in the course of denaturation: (a) triple-helix collagen molecule (hyperhelix), (b) breaking of noncovalent bond in a collagen molecule, and (c) a polypeptide helix transforms into separate glomerules (trimers, dimers, and single gelatin chains).

 

Fig. 6. Secondary structures of the crest of a polypeptide macromolecule: (1) glomerula, (2) a -helix and its notation, (3) b -fold and its notation, and (4) reverse point.

In other words, the synthesis of a DG layer before the recording process is accompanied by the appearance of stresses applied to "springs" representing the helical fragments of gelatin macromolecules (fig. 6). Then, the action of light plays the role of a trigger, which sets these springs free. The energy stored in these springs induces a cascade of phase changes in the state of a gelatin layer. These phase changes give rise to variations in the macroscopic characteristics of a recording medium

E LEVELS OF STRUCTURE ORGANIZATION OF A GELATIN LAYER

Gelatin is a highly asymmetric linear polypeptide polymer of protein nature. Macromolecules of gelatin consist, on the average, of 500-600 amino acid radicals. The molecular mass of gelatin macromolecules ranges from 40 000 to 1000 000. Gelatin is a high-molecular compound characterized by its ability to form various hypomolecular structures.

There are six basic levels in the structure organization of proteins (Fig, 7 ). The primary structure is determined by the composition and the sequence of amino acid radicals in a macromolecule of the polypeptide chain.

The secondary structure is determined by the configuration and relative spatial arrangement of protein macromolecules, which have the shape of helixes, folds, or glomerules (fig. 6).

The hypersecondary structure is determined by the aggregation of secondary-structure elements into a single macromolecule, which is manifested, in particular, as the phase state of the globular nucleus.

The next organization level- the domain structure is determined by external parameters (the thickness of a layer, the degree of adhesion of the layer to a substrate, etc.) responsible for the formation of separate and relatively weakly bonded globular segments of a macromolecule.

The ternary structure is determined by the conformation of protein helixes in the form of fibrils or globules.

The quaternary structure is determined by aggregation of protein fibrils and globules and. similar to the domain structure, is highly sensitive to external conditions (the conformation of a collagen-like triple hyperhelix is the limiting case of the quaternary structure for gelatin macromolecules). Distinguishing between the levels of structure organization of macromolecules, we assume that interactions of different types have distinct boundaries, and nonadjacent elements in the molecular chain or elements of different levels do not interact with each other.

Collagen - a family of natural polymers of protein nature - is a primary aggregate of gelatin macromolecules in living organisms, which provides the starting material for the formation of gelatin. The secondary structure of collagen has a shape of a left-handed hyperhelix consisting of three helical gelatin macromolecules. The chemical composition and physical and mechanical properties of gelatin strongly depend on the prehistory and the ways of transformation of collagen into gelatin. The main stages of transformation of collagen into gelatin involve the breaking of transverse bridge bonds between polypeptide macromolecules, resulting in the formation of tropocollagen, and separation of helical chains in protein (Fig. 5). The molecular mass of gelatin macromolecules is equal to approximately one-third of the molecular mass of initial collagen.

Secondary structures of gelatin

Destruction of a triple helix of collagen is accompanied by the formation of single polypeptide chain macromolecules. In certain cases, monomer (a -component), dimer (b -component), and trimer (g -component) fractions may also arise (fig. 5). The molecular masses of a -, b -, and g -components of gelatin are related to each other as 1 : 2 : 3. The existence of three fractions of gelatin with a considerable difference in their molecular masses indicates the polymolecular nature of gelatin and the nonuniformity of its properties. Gelatin with a higher uniformity is characterized by a higher quality. Monomolecular a -gelatin with a molecular mass of 40 000-100 000 possesses the best properties. To estimate the quality of gelatin in the synthesis of DG layers, one can employ the viscosity coefficient of aqueous solution of gelatin.

The secondary structure of the crest of a polypeptide macromolecule is usually considered as consisting of a glomerule, a -helix, b -fold, and reverse points (Fig. 6). On the average, protein molecules contain 35% of a -helixes, 15% of b -folds, 25% of glomerules, and 25% of reverse points. The mean length of an of a -helix is equal to 17 Å, and the sizes of a of b -fold are usually 20x25 Å. The overall linear size of a macromolecule may reach 30 000 Å with a diameter of 14 Å. The a -helix-glomerule phase transition at the level of the secondary structure occurs within the temperature range of 20-25C.

In the biochemistry of proteins, a - and b -structures are considered as nuclei for the coagulation of protein macromolecules into a compact (globular) conformational state. Reverse points play a passive role in the process of coagulation, forming fragments with minimum resistance to nonvalent forces that tend to bend the chain of a macromolecule as a whole. The functional activity of a protein macromolecule is determined by fragments free of a - and b -structures. Note that a -helixes, which are produced due to interlink hydrogen bonds, are characterized by more local interactions than b -folds. Therefore, chromium ions introduced into a gelatin layer at the stage of preparation of DG films are localized with the maximum probability near glomerate segments of macromolecules and near reverse points.

Hypersecondary and domain structures of gelatin

The formation of secondary a -and b -structures occurs immediately after the biosynthesis of a macromolecule. Next, a -helical cylinders are packed in an energy-favorable manner. A crystal is the state with the minimum free energy for a large number of identical units. The dynamics of coagulation or assembling (packing) of secondary structures can be interpreted as the motion of separate segments of a macromolecule. The introduction of the domain level for the description of the structure of a macromolecule is dictated by the necessity to take into account external parameters, including adhesion to a substrate and limited sizes of a pore where a molecule is located. From the general physical standpoint, the existence of domains within a macromolecule implies that a quasi-crystalline structure can be produced within a separate fragment of a macromolecule.

Ternary structures of a gelatin layer

If the intermolecular interaction of two neighboring protein molecules is stronger than the interaction of separate fragments within a structure unit, then linear fibrillar structures can be produced. In the case when the interaction inside a structure is stronger than the intermolecular interaction, globular forms of protein may arise (Fig. 7). Both of these ternary hypomolecular structures have a monomolecular character. Therefore, native (natural) proteins are divided into fibrillar and globular ones. Conformational transitions between the ternary hypomolecular structures are reversible. The condition for such transitions is a viscous-flow or dissolved state of proteins. Both of the ternary conformations specified above are characteristic of gelatin. The globular form is preferable in dilute solutions. In strong solutions and gels, the considered conformations coexist, but the fibrillar form is predominant. The fibrillar conformation predominates in thin gelatin films on substrates ensuring a high adhesion of gelatin.

Quaternary structures of a gelatin layer

Formation of coarsely dispersed ternary gelatin structures results in the appearance of boundaries between these structures, and the action of surface forces leads to the aggregation of ternary hypomolecular structures, i.e., formation of quaternary structures (Fig. 7). The forces of surface interaction are of the same nature as the forces of intermolecular interaction. The sizes of protein aggregates range from 1 to 10 m m, which allows us to classify these aggregates as colloidal particles. Ternary and quaternary structures of gelatin determine physical and mechanical, viscosimetrical, and surface properties of gelatin films.

CONTROL OF THE STRUCTURE OF A GELATIN LAYER

Macroscopically, in the preparation of a DG layer, gelatin as a polymer system passes through a sequence of different aggregate states. The initial state in this sequence is a dilute solution of gelatin in water, where macromolecules reside in the state of a Gaussian glomerule, or a globule. In the process of DG-layer preparation, as the solution is poured onto a substrate, the interaction of chain macromolecules gives rise to the formation of gel, which may feature properties of a liquid crystal in the case of rigid-chain molecules or properties of a strong solution with equal volume portions of a solvent and a polymer.

As the solvent (water) is evaporated out of the emulsion poured onto a substrate, macromolecules return to the native state, forming a collagen-like triple helical structure. The deformation degree of this structure is determined by conditions of film formation. In the case of gelling, the forces acting from the side of a substrate and conditions of drying lead to the unfolding of macromolecules into linear structures with simultaneous twisting of segments of these structures into helixes. Depending on the thickness of emulsion applied to a substrate, films obtained by molding through gelling on solid substrates feature a planar orientation of their structure elements. Obviously, the state of structure elements in a film depends on the state of these elements in emulsion solution. Specifically, gelatin in a film obtained from solution at a temperature higher than 35 C has a conformation of a Gaussian glomerule and does not display any features of ordering and planar orientation of structure elements. The degree of adhesion of emulsion to a substrate can be controlled with the use of a gelatin sublayer with a thickness of 0.5-1 mkm having a variable degree of hardening or a sublayer of a 5-10% solution of sodium or potassium silicate (liquid glass).

Thus, in synthesizing and pouring DG layers, one can control the structure of a gelatin layer. Below, we describe procedures of such a control.

DG layers with the maximum helicity of the secondary structure

Layers of dichromated gelatin developed with the use of a standard technique or by water vapor were prepared in the following manner.

An aqueous solution of gelatin with a weight content of dry gelatin from 0.5 to 6% was filtered, degasified, and poured simultaneously with cooling down to 30-35 C onto a glass substrate heated to the same temperature. The substrate was placed horizontally on a heated thick glass sample. For gelling, the plate poured with solution was kept in a cooler at a temperature of 5-10C during 4-6 h. The thickness of the DG layer thus prepared mainly depends on the initial concentration of gelatin solution. The DG layer was sensitized in an aqueous solution of ammonium bichromate at a temperature no higher than 20C during 5-7 min. The concentration of ammonium bichromate should not exceed the initial concentration of gelatin solution.

Otherwise, crystal structure may appear in a DG layer, and the intrinsic light scattering coefficient may increase for such a layer.

Preparation of DG layers with the temperature regime specified above ensures gelling with the maximum helicity degree of the secondary structure state. The minimum layer thickness, which can be achieved with low gelatin concentrations, allows one to prepare a gelatin layer with the maximum fibrillarity degree of the ternary structure. The required level of pre-exposure hardening of a gelatin layer is achieved with an appropriate dose of illumination of the prepared and sensitized DG layer with a UV lamp or sunlight.

DG layers with a globular structure

For the preparation of thin gelatin layers with a globular structure, 0.2-1.0% aqueous solution of gelatin was poured onto a substrate cooled down to 5C and then evaporated in a vacuum in accordance with the technique described above. For higher (up to 5%) gelatin concentrations, up to 20-30% of isopropyl alcohol was added to gelatin solution to prevent gelling (the Henderson method]). Then, such a solution was poured onto a substrate and dried in a vacuum.

For preliminary hardening, a 5% alcohol solution of hinone was added to gelatin solution before evaporation, which made it possible to produce a globular layer of nongelling gelatin.

To ensure a high intrinsic photosensitivity with respect to red light, ammonium bichromate (5-100% of the weight of dry gelatin) was introduced into gelatin solution. Upon the addition of ammonium bichromate to gelatin solution, all the procedures were performed under illumination with weak red light.

 

The holograms registered in photosensitive layers of several millimeters thickness have a number of specific properties, the most important of which are extremely high spectral and spatial selectivities. These highly selective gratings are used for the development of modern optical information processing devices, in optical memory systems with multiplex information recording and for interfiber connectors in optical telecommunication networks, for the variety of spectral filters for imaging, etc.Usual holographic materials can not be applied for recording of grating of millimeter thickness, because it is impossible to maintain the material uniformity during the post-exposure processing, Differential shrinkage caused by post-processing leads to the reduction of diffraction efficiency, and besides to the asymmetry and widening of selectivity contour of output signal. Selfdeveloping dichromated gelatin is one of the solutions to overcome these problems because it does not require post-exposure processing.

In the middle of the 1980th we realized new type of DG-system - selfdeveloping dichromated gelatin or gelatin-glycerol emulsion, which is not solid state media unlike ordinary DG. The developed photosensitive medium differs from the wellknown dichromated gelatin by the addition of certain amount of glycerol. Glycerol in these layers serves as the developing component and also as the plastic component. It keeps some amount of water molecules that are carrying out the developing process due to their hydrogen ties. And besides glycerol provides enough plasticity to the material to make layers of millimeter thickness.

However several problems arise at synthesis of superthick (more than 0,5 mm) layers. We have to find the reasonable limit of the emulsion drying time. Very long drying (more than three day) time is preferable, it leads to better gelatination and "ripening" of colloidal medium. However, long time drying is not suitable from the technological point of view. Our attempts to solve this by conventional methods such as ventilation by hot air or alcohol dehydration were not successful, they result in originating of a strong gradient of optical refraction in the layer depth. The processing of colloidal layers by microwave radiation resulted in their flaking from the substrate and to unmonitored change of the conformation gelatin macromolecules status.

Synthesis of selfdeveloping dichromated gelatin layers.

The procedure of the sample preparation is the following:

the gelatin is solved during 1hour in water (1 g of gelatin on 5 ml of distilled water) at temperature 50oC, then glycerol (0.8 ml in 5 ml of water) was added, and the solution was maintained at temperature 40oC within 2 hours.

Then we added ammonium bichromat of necessary concentration (20 % of the weight of dry gelatin or 0.2 g in 5 ml of a water) in the obtained homogeneous solution. Then ammonia for achievement of pH=9.0 was added, then the stain methylene blue (MB) as solution of 10 mg of the stain in 100 ml of water was added.

The prepared emulsion solution filled up the transparent pan with lateral walls of the necessary altitude (from 0.5 up to 3mm), and it was covered by special glass. Gelatination procedure was carried out at the temperature of 25oC within 24 hours. In outcome the layer of the given depth was received.

KCl doped emulsions were tested to investigate the possibility of chemical control of the SD DG structure. KCl was added during the emulsion preparation in the amount of several percent.

We used the gelatin sublayers to investigate the influence of adhesion from substrate. The substrate was covered with 1% gelatin water solution. After drying the sublayer of about 1 micron thickness was obtained. Then it was hardened in the Orwo-400 solution during the various time intervals to achived the sublayer different hardness. It is important to take into account the influence of substrate properties in variety of applications, particularly, for interfiber connectors, where the substrate role is played by bridged fibers.

The water structure and its control by means of the IR laser annealing

The SD DG system contains water in quantity sufficient for the hologram development. The water in such system is held with the help of glycerol and consequently the holographic properties depend on glycerol concentration in a system. This system contains great many of water, and, therefore it is possible to consider it almost as aqueous solution, to which the quasicrystal liquid structure role is essential. The collective character of the water molecule motion is confirmed by the molecular dynamics results.

It is possible to influence on SD DG structure in all volume by means of the laser IR radiation. IR electromagnetic radiation causes molecular rearrangement in the material. This effect consists in the loss of coordinate oscillations stability: the part of molecules does not return in the position with initial coordinates. It is impossible to estimate the optimal radiation wavelength for such annealing because of composite emulsion structure. Therefore, basing on the known data on absorption spectrum of water we chose 1 micron wavelength radiation. Besides it has another advantage that the IR near range radiation passes through the glass substrate and consequently in thicker layer there are no undesirable effects of an interference of IR radiation.

Technique of the laser annealing

After holding the emulsion layer during a day the quasicrystal selfdeveloping dichromated gelatin structure was formed. Then the plate was subjected to IR laser radiation with 1 micron wavelength and with known values of power in the pulse. In order to eliminate the influence of all transition processes, the hologram was recorded 10-12 hours later.

The holographic characteristics measurement.

We illuminated samples with interference pattern constructed by two plane light waves from the He-Ne laser. The spatial frequency of the recorded diffraction grating was hundreds lines/mm. The energy of two beams was 6mW. Diffraction efficiency was measured as the relation of intensity values of diffracted and input beams.

The IR laser annealing results

The variable parameters for the annealing IR pulses are the pulse energy, duration, and shape. It should be mentioned that maximal diffraction efficiency obtained in SD DG layers is about 70%. However when we analyzed the effect of different factors on the diffraction efficiency we were working in the range of 5-10% efficiency in order to eliminate the influence of non-linear properties of medium.

The experimental results for IR laser annealing are shown in Fig. 8 (fig. 1 from the paper) for holographic grating of 600 lines per mm recorded in selfdeveloping dichromated gelatin layer of 1mm thickness by radiation of He-Ne laser. We analyzed the dependence of diffraction efficiency on the amount of IR laser annealing pulses and full pulses energy (Ean) and the best result occurred for six annealing pulses. Figure 8 shows the obtained diffraction efficiency of holograms increasing m=[(DEan DE0 )/DE0 ]100%, where DEan is the diffraction efficiency of the IR laser annealing SD DG test hologram and DE0 is the same for SD DG test holograms without laser annealing. One can see from this figure that there is an area of considerable diffraction efficiency increasing. The best result received at an annealing by six pulses with duration 3 msec at full impulses energy equal to 18-30 J. However, the exact energy level depends on the material thickness, on the concentration of gelatin in emulsion, and on the type and series of gelatin. It should be pointed out that all obtained values of diffraction efficiency for the annealed materials are higher (on average 2-3 times) than they are for the plates not subjected to the annealing. It is visible that the diffraction efficiency curve (Figure 1) has the brightly expressed peak (for annealing energy more than 20 J) at small pulse duration. Further increase of pulse energy leads to considerable diffraction efficiency increasing.

 

Figure. 8. Diffraction efficiency of holograms recorded in selfdeveloping dichromated gelatin layers with different energy of IR laser annealing pulses with 3 msec duration of six annealing pulses.

The pulse irradiation regime for laser annealing is preferable, because it allows to estimate precise energy of effect on the layer structure. The pulse irradiation is to some extent like sharp system shaking, and the necessary macromolecules packing is reached by the following relaxation processes in the system.

In our opinion IR electromagnetic field causes impulsive disturbance of water at the level of collective modules while single water molecules and gelatin squirrels do not absorb radiation of 1 micron wavelength9. Water quasicrystal net rearrangement conducts the change of electromagnetic field affecting gelatin macromolecules. These macromolecules move under of this field action and change therefore tertiary and quaternary conformation status to achieve an energy minimum in new quasicrystal net. Thus spiral segments do not change, and this means that the SD DG system photosensitive properties do not change too. (Our conception consists in the material photosensitivity based on untwisting of spiral segments.)

In general our experiments showed that the variety of pulse parameters affect on the resulting diffraction efficiency value. The main parameter is, of course, the amount of energy absorbed by the material. However, the pulse duration and its shape (this means the sharpness of fronts) as well as the moment of the annealing relatively the emulsion maturing time are also of importance. It is obvious from the experiments that there exist several solutions to reach the maximal diffraction efficiency by combining the optimal pulse energy, shape, duration and amount of pulses. However that concerns the moment of annealing, multiple experiments showed that the optimum is around 24 hours after emulsion pouring on substrate

The influence of adhesion to substrate on the selfdeveloping dichromated gelatin structure

Experiments showed that SD DG layer separation from glass substrate often occurs causing the diffraction efficiency reduction. This effect is called photoinduced collapse of the emulsion at recording. For elimination of this phenomenon we proposed to utilize an additional gelatin sublayer with the hardness higher than it is for the photosensitive emulsion layer. We investigated what optimal value of the sublayer hardness. The dependence of holographic properties of the SD DG layer on the substrate hardness is shown in Fig. 9 (fig. 2 from the paper). One can see from the Figure 9 that the maximal diffraction efficiency was observed for the sublayer subjected to hardening in ORWO-400 during 4.5 munites (corresponds to H=4.5).

Fig. 9. Influence of hardening degree of sublayer on the SD DG exposition characteristics.

SD DG emulsions containing high-molecular-weight polymer

We developed the new version of selfdeveloping dichromated gelatin, in which 50 % of glycerol in emulsion was replaced by natural polymer (polysaccharides similar to stratch) obtained from plants, its molecular mass is about 20,000. The first experiments showed considerable reduction of the layer gelatination time (Figure10 fig. 3 from the paper). The formation of quasi-crystal structure occurs faster in this case compared with initial version of SD DG. Obtained holograms have improved storage time.

Fig. 10. Influence of the gelatination time on the SD DG exposition characteristics for 50% polymer replacement of glycerol.

The SD DG emulsion doped by KCl

We investigated the influence of salt addition to the composition. We used KCl, because it is known that K ions affect the aquacomplex structure. The experimental results are shown in Figures 12(a) and (b) (fig. 4 from the paper). It is found that KCl essentially improves photosensitivity of the emulsion. The shape of the diffraction efficiency contours changes under the influence of KCl, however the character of this change depends on gelatination temperature schedule.

 

Fig. 11. The hologram diffraction efficiency for SD DG doped by KCl in the gelatination time dependence at temperature 24 (a) and at temperature 00 (b).

CONCLUSIONS

We proposed different technologies to control the holographic characteristics (diffraction efficiency, storage time) of selfdeveloping dichromated gelatin material.

It was shown that IR laser annealing before hologram exposure results in increase of diffraction efficiency.

In order to overcome the problem of the photosensitive layer separation from the substrate we proposed to use strongly hardened gelatin sublayers. It was shown experimentally the improvement of diffraction efficiency in this case.

It was shown that the storage time of hologram can be improved by replacement of part of glycerol by natural polymer with high molecular weight.

Addition of salt to the emulsion leads to the increase of the material photosensitivity and to the diffraction efficiency improvement due the influence of ions on water molecules inside the material.

REFERENCES

  1. Erko A.I., Malov A.N. Development parameters optimization of the dichromated gelatin layers for optical information recording. / Scientific and Applied Photography. 1980.- vol. 25 N 3 pp. 185-187.
  2. N.F.Balan, A.I.Erko, V.V.Kalinkin, A.N. Malov. et al, USSR Patent no. 1347757. 1985.
  3. V.P. Sherstyuk, A.N. Malov et al., Some principles for formation of self-developing dichromate media, Proc. SP1E, 1238, pp. 218-223, 1989.
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  5. S.P. Konop, A.G. Konstantinova,A.N. Malov, Mechanism of the hologram recording in self-developed dichromated gelatin layers, Photonics & Optoelectron., 3, 21-29, 1995.
  6. Consnantinova A.G., Malov A.N., Conop S.P. The selfdeveloped dichromated gelatin films for holography. / Proc. SPIE. 1996. - Vol. 2969. - pp. 274-277.
  7. N.Reinhand, Yu.Korzinin, I.Semenova. Very thick holograms: manufacturing and applications, Journal of Imaging Science & Technology, 41, 3, 241, 1997.
  8. Vigovsky Yu.N., Malov A.N., Malov S.N., Konop S.P. Photoinduced Phase Transitions in Hologram Recording in Layers of Dichromated Gelatin. / Laser Physics. 1998.- vol.8 - 4, pp. 901-915.
  9. Vigovsky Yu.N., Malov A.N., Malov S.N., Fetshenko V.S., Konop S.P. New dichromated gelatin technologies for the diffraction optical elements fabrication. / Proc. SPIE. - 1998.- vol. 3347- pp.314-324.
  10. N.Reinhand, Yu.N.Denisyuk, N.N.Ganzherli, I.Maurer, I Pisarevskaya, V.Markov, Application of selfdeveloping dichromated gelatin for holographic data storage, Proceedings SPIE(Photonics West98), 3294, pp.22-30, 1998.
  11. .Yu.N.Vigovsky, S.P. Konop, A.N. Malov, S.N. Malov, Photoinduced phase transitions in layers of dichromated gelatin, Laser Physics,. 8, N 4, pp. 901 - 915. 1998.
  12. L.E. Kruchinin, I.V. Bogdan, Yu.S. Zagaynova, Yu.N. Vigovsky, A.N. Malov. Selfdeveloped colloidal recording media for fiber interconnects and holographic elements fabrications, Proceedings of the First Asia-Pacific Conference on Fundamental Problems of Opto- and Microelectronics APCOM2000, SPIE RFFR: Vladivostok, 2000. pp. 55 59.
  13. L.E. Kruchinin, I.V. Bogdan, Yu.S. Zagaynova, Yu. N. Vigovsky, A.N. Malov, Optoelectronic applications of the selfdeveloped colloidal holographic recording media, Proc. SPIE, 4513, pp. 142 146, 2001.
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