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SOGOKON' A. B.
ON THE LAYERS OF THE BICHROMIZED GELATIN
Are investigated the spectral characteristics of the Lippmann images, obtained on the layers of the bichromized gelatin (BKHZH). It is shown that the color of image depends not only on the wavelength of emission, but also on its intensity. This is connected with the heterogeneous swelling of gelatin and with a change of its structure in the nonirradiated sections with the rapid dehydration.
The uncommon properties of Lippmann photographs on BKHZH can be used for preparing the selective mirrors, for mapping of graphic information, and also for registration and image processing.
Is known  the method of obtaining the colored images, based on the registration of standing waves in the volume of thick transparent photographic emulsion. The period of the registered interference structure is unambiguously connected with the wavelength of that falling to the layer of emission, which ensures the correct color reproduction of the photographed image with the illumination by its white emission. Because of the great technical difficulties in its time this method did not obtain wide application.
The development of holography led to the creation of the fundamentally new technique of experiment and new recording media. Appeared communications about the record of Lippmann photographs on the contemporary emulsions of the type LOI-2 [ 2,3 ] and on the layers of the bichromized gelatin (BKHZH) [ 4,5 ]. Purpose of this work - study of the special features of the Lippmann photographs, obtained on the layers BKHZH, the mechanism of shaping of images and possibilities of their practical application.
Procedure and the results of the experiment
For the preparation is layer BKHZH the basis it is undertaken the method Lina . The holographic plates Of pe-2 and LOI-2 they fixed in the acid fixative, washed in the running water and dried at room temperature. The sensitization of the dried plates was conducted directly before the exhibition. For this plate was immersed on 5-15 min in 1-5%- ache the solution of dichromate of ammonium and after its runoff dried in the jet of hot air or in the cabinet drier at a temperature 100-150°. Duration of drying 3-5 min.
Fig. 1. Installation diagram for the contact printing Lippmann photographs; 1 - luminous source (laser or mercury-vapor lamp), 2 - lens, 3 - negative, 4 - layer BKHZH, 5 - the mirror
The installation diagram for the printing of Lippmann photographs is given in Fig. 1. They direct the extended laser beam to the negative, located before the recording medium, the passed emission is reflected from the flat mirror and, being extended in the opposite direction, is formed in the volume of the recording medium the standing wave, whose amplitude depends on the transmission of negative. As the radiation sources were used the lasers LPM-YY (442) and LIE -21 (337 nm) and mercury-vapor lamp DRSH-2SHCH0 (365, 436 nm). Furthermore, by means of the usual photographic enlarger was achieved the direct projection printing of enlarged images. The regime of working the plates exposed practically was differed in no way from the regime of working BKHZH for obtaining the holograms [ 7 ].
The images, obtained employing the procedure given above, have a number of interesting properties. With the examination of image in the reflected light (a subnormal incidence in the light) different sections of image depending on the density of initial negative acquire different color. Under the transparent sections is obtained the image of dark-blue color, while under the opaque - red. The semitones of negative are transferred by nuances within the limits from the orange to the green. Hence it is possible to draw the conclusion that the period of the interference structure, fixed in the layer BKHZH, depends both on the wavelength of emission and on its intensity.
If we arrange Lippmann imprint on the sheet of black paper and to examine at large angle, then usual black and white image is observed. Under the transparent sections of the negative of gelatin it remains transparent, while under the opaque acquires milk-white tone. In this case the image is constructed not due to the luminous absorption, but due to its scattering, which resembles the properties of images on the vesicular materials . For investigating the dependence of the color of image on the exposure level on one plate they achieved a number of exposures by the uniform collimated laser beam or photographed the image of sensitometric wedge, and then the spectra of the transmission of the obtained images were measured.
Fig. 2. Characteristics of Lippmann the image: and, g - dependence of the spectra of the transmission of the images from the exposure level with the record by the emission heliumcadmium (442 nm) and nitric (337 nm) lasers; b and d - dependence of the density of image on the exposure for the same wavelengths; C - the dependence of the color of the image from the logarithm of exposure (curve 1 - 442, curve 2 - 337 nm); e - dependence of the half-width of the spectra of the transmission of the images from the exposure (1 - 442, 2 -337 nm)
Fig. 2 depicts the spectral characteristics of the images, obtained on the plates Of pe-2, sensitized by the 1%- by the solution of dichromate of ammonium during the exhibition by the emission of lasers LPM-YY (Fig. 2, A) LIE -21 (Fig. 2, g). From the analysis of spectra follows that depending on exposure level the width of reflection spectra (Fig. 2,e) changes, the wavelength of the maximum of reflection (Fig. 2, c), and also the density of image (Fig. 2, b, d). It should be noted that the wavelength of the maximum of reflection with the long exposures does not correspond to the wavelength of the emission of record. This is connected with the fact that in the process of treating the layer an increase in the period of interference structure occurs. The wavelength of the maximum of reflection linearly depends on the logarithm of exposure (Fig. 2, c), which gives the possibility to write down
where - the wavelength of the maximum of reflection with the high energy of exposure (wavelength of saturation), H - energy of exposure, k - constant of proportionality, which can be interpreted as the coefficient of the color contrast.
With the conversion of the color of image occurs a change in its density (Fig. 2, b, d). These dependences are analogous to the characteristic curve of blackening of the usual recording media. However, the photographic latitude of linear section is considerably less, and in the field of the long exposures is observed the especially large spread of experimental points, which it is not possible to explain by error of measurements. It is possible to assume that the dependence of image in the region of saturation bears the oscillitory nature, for example, as shown in Fig. 2, d.
Mechanism of the formation of the images
In the process of the preparation of plates for the sensitization they prolonged time (about 1 h) find in the water. As a result of this gelatin it swells, long protein molecules untwist and they attempt to form the linear arrays. To molecules, which are been located on surface layer, this succeeds to the larger degree than for molecules, which are located in the depth, since they to a lesser degree experience the resistance of adjacent molecules. In the razbukhshem layer is obtained the heterogeneous tanning, which grows from surface layer to the base layer. The surface molecules of gelatin, which formed the linear arrays, no longer can accomplish work, they occupied energetically advantageous position, while molecules, which are located in the depth of layer, they have a certain reserve of potential energy, since interaction of some with others and with the molecules of tanning matter does not make possible for them to be erected into the linear arrays. Tanning can be determined by value, to the inversely proportional work, accomplished by molecules with the working in the water. Layer is not tanned, if molecules realize entire stored potential energy, and it is tanned, if potential energy with the working in the water does not realize. The potential distribution energy along the thickness of the razbukhshego layer can be schematically presented, as shown in Fig. 3, A.
Let us examine the processes, proceeding with swelling of those exposed it is layer. In this case we consider that the photochemical transformations Cr(.VI) into S.r(.III) in the gelatin occur in accordance with the model, described in the work [ 9 ]. The number of photos-seam between the molecules, which were being formed in the antinodes of standing wave, is small with low energies of exposure, summary binding energy between them is also small, and the potential distribution energy of the molecules of the swollen layer takes the form, shown in Fig. 3, b. furthermore, with the prolonged working in the water together with swelling of layer in the knots of standing wave can occur the local dissolution of gelatin, i.e. the hydrated molecules acquire relative freedom, changing the structure of gelatin, but they cannot leave layer because of the tanned sections in the antinodes. In the works [ 10,11 ] it is shown that the structure of gelatin changes both with working of layer in the water and in the process of drying. Therefore with the working by isopropanol a change in the structure of gelatin in the knots and the antinodes occurs differently, i.e. with the rapid loss of water of molecule they do not manage to return to the initial state and they are forced to form the new molecular network, different from that, which is obtained with usual gel-NII - Scientific Research Institute or slow drying. In the knots of standing wave gelatin density decreases due to an increase in the volume of layer, while in the antinodes it increases due to structure change under the action of that forming Of s.r(.III). As a result of gelatin the elasticity loses, and in the layer the increased period of interference structure is fixed. With an increase in the exposure grows modulation of potential energy of the razbukhshego layer. The number of constant-phase surfaces, recorded in the layer, increases (Fig. 3, in, g, d), the width of reflection spectra and displacement into the red region decrease, and diffraction effectiveness rises.
By a change in the structure of gelatin it is possible to explain the formation of black and white image. The destructured sections strongly scatter light, which gives milk-white form to them.
Consideration of the results
Uncommon properties of Lippmann photographs on the layers BKHZH can be used for preparing the selective mirrors, for obtaining the pseudo-colored slides from the black and white negatives, for registration and image processing.
The possibility of using the Lippmann photographs as the selective mirrors directly follows from Fig. 2. The wavelength of reflection and half-width depend on exposure level. In this case the reflection coefficient attains 99%, which makes it possible to use such mirrors in the resonators of lasers, in the Fabri-Perot interferometers, and also as the beam splitters in the holographic devices. The cost of them is considerably lower than interference dielectric mirrors, and in this case is a possibility of preparing the mirrors of practically any sizes and creation of any distribution of spectral characteristics in the plane of mirror.
Fig. 3. Diagram, which elucidates the dependence of the period of the interference structure from the exposure level: and - the distribution of the tanning in the razbukhshem unexposed layer; b, in, g, d - modulation of the tanning in the razbukhshem layer depending on the exposure
The pseudo-colored slides, obtained from the black and white negatives, can be used for mapping of graphic information, for example diagrams, tables, graphs. Slides can be demonstrated both in the transmitted light by usual kadroproyektorom and in that reflected with the application of an epidiascope. The second version should be given preference, since with this more fully is used color range and is reached higher high-contrast image. With the printing from the black and white negatives the value and in equation (1) can be represented in the form
where - the intensity of light, which falls to the negative, the smallest density of negative (density of veil), density of image, time of exhibition. After substituting these values in (1), we will obtain
whence it follows that a change in the color in the Lippmann photograph is linearly connected with the density of negative. Recently increasingly more frequently is used the idea of complex spatial distributions of different physical quantities by means of the conditional it is color, for example, with digital processing of images [ 12 ]. To Lippmann photographs on BKHZH this property is inherent by their nature itself. In this case Lippmann "painting" has the advantage that the obtained image can be subjected to further optical working. Examining the pseudo-colored image through the light filter with the passband , we will observe the details of initial image, which are located in the density range .
By a change in the wavelength of light filter it is possible to separate the image details interesting, and by changing its half-width - range of densities interesting. If the image, observed through the interference light filter, photographed on the contrasting photographic material, then it is possible to obtain the images of the lines of identical density - equidensities. For the illustration is carry ouied processing the image of planet Jupiter. For this from the astro-negative they printed image with an increase by the layer BKHZH. The obtained image they photographed through the interference light filter with = 640 nm and = 90A. Fig. 4, and depicts the photograph of initial image, while on Fig. 4, b, C - to a series of photographs with the different angles of the slope of interference light filter, i.e. with the different and . It is evident that even under the conditions for the incorrectly set experiment (reconstruction of the wavelength of light filter was achieved via its inclination) on the obtained images it is possible to reveal more interesting details, than on the initial negative.
Fig. 4. Isolation of equidensities on the image of planet Jupiter: and - the imprint of siskhodnogo astro-negative; b - photograph of the Lippmann image, obtained with the interference light filter with the different angles of its inclination in the reflected light; C - the same, but in the transmitted light
However, with the two-stage process unavoidably are shown distortions and noise, which appear during the first stage of registration. The granularity of images on Fig. 4, b is caused by the granularity of the material, on which is registered initial negative. Therefore the considerably larger volume of information can be extracted with processing of the Lippmann images, obtained with the direct registration. However, sufficiently small sensitivity it is layer FOR BKHZH it does not make possible to directly record the images of other astros-object, except the sun. The direct registration of Lippmann images possibly in biology. In this case the emission of lamp DRSH-2SHCH0 it is completely sufficient for obtaining the images with increase in 30-100x.
Thus, the Lippmann photographs, obtained on the layers BKHZH with the use of sources of monochromatic light, have properties, substantially different from the properties of usual Lippmann photographs. This is connected with the special features of the recording medium: the period of the fixed interference structure depends not only on the wavelength of incident radiation, but also on its intensity. As a result the possibility of the single-valued conversion of the intensity of light in the color appears. Simplicity of the diagram of obtaining Lippmann photographs, possibility of using the sources with the small length of coherence and high diffraction effectiveness of images open the great possibilities of the practical application of this method.
In conclusion the author considers as his pleasant duty to express appreciation To v. p. sherstyuk and L. ye. mazur for the valuable considerations, in. By a. kaminskoy and By l. ye. nikishinoy for help in conducting of spectrophotometric measurements and V. n. dudinova - for the kindly furnished astro-negatives.
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Kharkov state university im. a. M. of Gor'kiy