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Comparison of the effects of two bleaching agents on the recording of phase holograms in silver halide emulsions
Optics Communications 267 (2006) 356–361 www.elsevier.com/locate/optcom
Comparison of the effects of two bleaching agents on the recording of phase holograms in silver halide emulsions I. Ba´nya´sz
*
Department of Crystal Physics, Research Institute for Solid State Physics, P.O. Box 49, H-525 Budapest, Hungary Received 8 April 2006; received in revised form 20 June 2006; accepted 21 June 2006
Abstract Optical densities before bleaching and final Lin-curves of plane-wave phase holograms recorded in Agfa-Gevaert 8E75HD emulsions were determined for combinations of the AAC developer with a solvent bleach (R-9) and a (fixation-free) rehalogenating bleach (R-10). To characterize the processing, the square root of the diffraction efficiency of the processed holograms was related to the amplitude of the optical density modulation obtained at the development step. Sensitivity, linearity and dynamic range of the processes could thereby be compared directly. 2006 Elsevier B.V. All rights reserved. PACS: 42.40.i; 42.40.Eq; 42.40.Ht; 42.40.Lx; 42.70.Ln Keywords: Holography; Theory of holography; Photographic and recording problems; Holographic instrumentation and techniques; Light sensitive materials
1. Introduction A detailed description of holographic bleaching techniques can be found in the monograph of Bjelkhagen [1]. They can be divided into three main categories: conventional or direct (rehalogenating) bleaching, fixation-free rehalogenating bleaching and reversal (complementary) or solvent bleaching. In conventional bleaching the silver grains are converted into a transparent silver salt after fixation, i.e. the removal of the unexposed silver-halide crystals. In fixation-free rehalogenating bleaching the conversion takes place without a fixation step, so that the unexposed silver-halide crystals remain in the emulsion. In reversal bleaching the developed silver grains are converted into a water-soluble silver complex, which is removed from the emulsion during bleaching, leaving the original, unexposed silver-halide grains in the emulsion. Obviously, there is no fixation step before the reversal bleaching, as otherwise all *
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the unexposed and exposed silver halide grains would disappear after bleaching. Due to the considerable material removal in both conventional and reversal bleaching, the thickness of the emulsion is reduced. Fixation-free rehalogenating bleaching does not lead to emulsion shrinkage. One of the first rehalogenating bleaches used in holography was Kodak R-10, as modified by McMahon and Franklin [2], applied after a fixation step. Van Renesse and Bouts wrote an excellent study of the various bleaching agents used in holography [3]. One of the bleaches used in those experiments was also a version of Kodak R-10 (with fixing). They came to the conclusion that phase variations in the bleached holographic emulsions were determined by the electric polarizability and volume of the molecules of the silver compound formed. Schmackpfeffer et al. [4] studied the optimisation of the generation of high-efficiency holographic gratings in bleached silver halide emulsions. They recorded phase holograms in Agfa 8E70 emulsions, using Kodak HRP developer, fixed in Agfa G334, and bleached with either R-10 or Kodak EB-2 bleaches. They
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
found that Kodak R-10 bleach resulted in the highest diffraction efficiencies. Kumar and Singh [5] also used a modified version of R-10, with a fixation step, along with four other bleaching agents, to try to improve the diffraction efficiency of phase holograms recorded in Agfa-Gevaert 8E75 HD emulsions. They found that bleaching agent R-10 gave the highest diffraction efficiencies over a wide range of bias exposures, together with ferric chloride bleach. As for scattering, R-10 produced somewhat lower levels than the ferric chloride bleach at higher exposures. The fixation-free version of rehalogenating processing was discovered by Hariharan [6]. Crespo et al. [7] recorded high-efficiency (up to 70%) reflection gratings in AgfaGevaert 8E75 HD plates with fixation-free rehalogenating bleaching, using various bleaching agents, including R-10. They too found that it was R-10, which resulted in the highest diffraction efficiencies and lowest scattering. Kumar and Singh [8] obtained holograms with diffraction efficiencies up to 87% at a wavelength of 442 nm in Kodak 649F emulsions, using D-19 developer and a slightly modified R-10 bleach, without a fixation step. Kostuk [9,10] applied a factorial optimisation for the constituents of the R-10 bleach. He recorded reflection gratings in Agfa-Gevaert 8E75 HD and Ilford SP673 emulsions, using a variant of the CW-C1 developer [11] and the modified R-10 bleach, without fixing. He concluded that the best composition of R-10 had a high concentration of rehalogenating agent (KBr) and low concentration of oxidizer and sulphuric acid. It was Kiemle and Kreiner [12] who first applied reversal bleaching to holography. Buschmann [13] studied three bleaching processes, including R-9, with and without fixation step in Agfa-Gevaert 8E75 holographic emulsions at a wavelength of 647 nm, at a spatial frequency of 1545 lp/mm. He related the diffraction efficiency of the final phase gratings to the pre-bleach optical density of the initial absorption gratings. According to his results, R-9 with a previous fixation step gave somewhat higher efficiencies than without fixation, but that processing also resulted in considerably higher (some 2.0 dB) scattering. Hariharan and Chidley published a series of papers on the effects of bleaching agents on the diffraction efficiency and signalto-noise ratio of phase holograms. In the first [14] they recorded plane-wave phase holograms in Agfa-Gevaert 8E75 HD plates at a wavelength of 632.8 nm and interbeam angle of 45. They compared the diffraction efficiencies and scatterings of the holograms obtained using the combinations of a conventional bleach and the R-9 reversal bleach with 5 different developers, with (in case of conventional bleach) and without (in case of R-9) fixing. They found that solution physical development and local hardening of the gelatine during development were the main causes of the considerable differences in diffraction efficiencies and scatterings obtained. In another paper [15] they studied the effects of the type and concentration of the halide used in the rehalogenating bleaches on diffraction efficiency and scattering. They obtained the best results
357
with low concentrations of KI as a rehalogenating agent. The same authors also studied the effects of conventional and rehalogenating bleaches as functions of the spatial frequency of the holographic gratings [16,17]. In spite of the very considerable literature of the field, of which some representative examples were enumerated above, our knowledge about bleached phase holograms is still far from being complete. For example, all the work mentioned above lacks a study of the dependence of the effects of processing on the visibility of the constructing interference pattern; the authors recorded the holograms over a range of bias exposures, but only for a fixed fringe visibility (usually at V = 1.0). However, it is the illumination difference between dark and bright fringes that drives the physical and chemical processes that take place at the development step, and, indirectly, those taking place during bleaching. The author of the present paper and his co-authors extended the study of the processing of both amplitude [18] and phase [19] holograms to the whole range of visibilities of the recording interference patterns. The present work deals with the comparison of the effects of fixation-free rehalogenating and solvent bleaching on the diffraction efficiency of holographic gratings recorded in Agfa-Gevaert 8E75 HD plates over a wide range of bias exposures and fringe visibilities. 2. Experimental procedure Plane wave holograms were recorded on Agfa-Gevaert 8E75HD NAH emulsions on rectangular glass substrates with dimensions of 64 mm · 64 mm · 1.5 mm. A helium– neon laser operating at 632.8 nm was used for recording and reconstruction. The interbeam angle was 45, thus the spatial frequency of the gratings was about 1200 line pairs/mm. For each processing combination, hologram pairs at seven values of fringe visibility, namely at V = 0.2, 0.4, 0.6, 0.8, 0.9, 0.95 and 1.0 were recorded. The corresponding beam ratios were determined from the following equation: pffiffiffi 2 R V ¼ ð1Þ Rþ1 where V is the visibility of the interference fringes and R is the ratio of the intensities of the two beams. The beam ratios were set by adjusting a variable beam splitter and inserting appropriate neutral density filters in the unexpanded object beam. Twelve hologram pairs at exposures ranging from 10 lJ/cm2 to 1.6 mJ/cm2 were recorded at each visibility. The total intensity at recording was maintained constant at 400 lW/cm2 ± 1% throughout the experiments. The first element of each hologram pair was developed and fixed to obtain an absorption hologram and the second was developed with the same developer and bleached, without a fixation step. The AAC developer, the composition of which is given in Table 1, was used throughout, at temperature T = 20 C. All the absorption holograms were fixed in Kodak F24 fixer for 5 min. Bleach-
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
358 Table 1 Composition and use of the AAC developer Name of the compound
Quantity
Ascorbic acid Sodium carbonate Distilled water
18 g 120 g 1l
Developing time Temperature
3 min 20 C
Table 2 Composition of the R-10 and R-9 bleaches Name of the compound
Name of the bleach R-10
R-9
Potassium bromide Potassium dichromate Sulphuric acid (cc.) Distilled water
35 g 2g 10 ml 1l
– 2g 10 ml 1l
ing was also performed at 20 C, and terminated 1 min after the plate became transparent. The composition of R-10 and R-9 bleaches is shown in Table 2. These experiments allowed us to compare the effects of two different bleaches (R-10 and R-9) used with the same developer (AAC). For both bleaches, all the holograms were processed simultaneously. After processing, the optical density of the absorption holograms and the diffraction efficiency of the phase holograms were measured. Care was taken to minimise the effects of stray light. When measuring low intensities (efficiencies below 0.1% and optical densities above 3) the detector was enclosed in a black box that admitted only light coming directly from the hologram, and the intensity of stray light was always checked. Both the optical density and the diffraction efficiency were corrected for reflection losses. In the case of the optical density measurements the intensity of the reflected beam was also measured and subtracted from that of the incident beam. In the diffraction efficiency measurements reflection losses were calculated from the Fresnel-formula instead of measuring the reflected intensity, because the latter proved to be uncertain due to the presence of interference fringes.
is the optical density, E0 is the bias exposure, and t0, E1, j and t1 are fit parameters. The square root of the diffraction efficiency against bias exposure and fringe visibility was fitted by the function [20] rðE0 ; V Þ ¼ f ðE0 Þð1 eV Þe
½V V 0 ðE0 Þ2 w2 ðE0 Þ
ð3Þ
where r is the square root of the diffraction efficiency, E0 is the bias exposure, V is the visibility of the interference fringes and f(E0), V0(E0) and w(E0) are parameter functions of the following form: 2 3 1 ParðE0 Þ ¼ ci01 4 þ ci13 5 E0 exp ci11ci12 þ1 2 3 1 4 þ ci23 5 i21 exp E0cc þ 1 i22 2 3 1 4 ð4Þ þ ci33 5 E0 exp ci31ci32 þ1 where ‘‘Par’’ stands for f, V0 and w, and cixx represents three sets of constants (i = f, V0, w). If E0 is the bias exposure and V the fringe visibility, the minimum (Emin) and maximum (Emax) exposures can be expressed as follows: Emin ¼ E0 ð1 V Þ
ð5Þ
Emax ¼ E0 ð1 þ V Þ
ð6Þ
Consequently, the amplitude of the density modulation at a bias exposure of E0 and visibility of V is: DDðE0 Þ ¼ DðE0 ð1 þ V ÞÞ DðE0 ð1 V ÞÞ
ð7Þ
This expression was used for the calculation of DD from the values of D obtained by fitting Eq. (2) to the experimental data. 4. Results and discussion An example of a D(E0) function fitted to measured data is shown in Fig. 1. The absorption holograms were devel-
3. Model functions The results of the measurements, optical density as a function of exposure and square root of diffraction efficiency as a function of bias exposure and interference fringe visibility, were fitted by analytical functions. The latter functions are also called as Lin-functions or Lin-curves after the name of the researcher who introduced them. The density against exposure curves were fitted by the following function [18]: where D 2 3 t0 6 DðE0 Þ ¼ 2 log 4 j E1 E0
þ1
7 þ t1 5
ð2Þ
Fig. 1. Measured (points) and fitted (solid line) D(E) function for AgfaGevaert 8E75HD, for phase holograms recorded at a fringe visibility of 0.2, and developed by AAC.
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
oped by AAC and fixed by Kodak F24, at V = 0.2. The parameters of the fitted function are t0 = 0.75, E1 = 37.5 lJ/cm2, j = 2.15 and t1 = 0.0075. r(E0, V) functions fitted to experimental data corresponding to the two bleaches are shown in Figs. 2 and 3. Parameters of the r(E0, V) function of the combination of AAC and R-10 are shown in Table 3. The parameters corresponding to the combination of AAC and R-9 can be seen in Table 4. The model is generally in good agreement with the measurements. However, large differences can be found in the case of the rehalogenating bleach (R-10), especially at visibilities V = 0.8 and 1.0 at high exposures (between E0 = 100 and 400 lJ/cm2). The strong dip in r can be attributed to the presence of noise gratings [21–23]. For this reason we used the measured values of r instead of the fitted ones to prepare the r(DD) characteristics. If we compare the above Lin curves, we can see that it is R-9, which gives higher diffraction efficiency, while the combination of AAC with R-10 reaches peak diffraction efficiency at a lower exposure. However, these characteristics provide no direct information on the mechanism of hologram formation.
359
Table 3 Parameters of the r(E0, V) function of Agfa 8E75HD Indices (xx)
cfxx
cðV 0 Þxx
cwxx
01 11 12 13 21 22 23 31 32 33
1.5 42 21 0 280 140 0 11.5 3.0 0
4.0 170 75.0 0.3 20.0 11.0 0.49 70 8.0 0.35
4.0 190.0 75.0 0.3 25.0 8.0 0.49 60 8.0 0.4
Developer: AAC, bleach: R-10.
Table 4 Parameters of the r(E0, V) function of Agfa 8E75HD Indices (xx)
cfxx
cðV 0 Þxx
cwxx
01 11 12 13 21 22 23 31 32 33
1.5 38 32 0 675 300 0 12.5 3.2 0
3.0 72 2.5 0.21 53.5 2.8 0.15 28 1.8 1.64
3.0 20.5 3.0 0.95 700 120 0.27 4 21 0.14
Developer: AAC, bleach: R-9.
Fig. 2. Measured (symbols) and fitted (solid lines) r(E0,V) curves for Agfa-Gevaert 8E75HD, for phase holograms processed by AAC developer and R-10 bleach. Visibilities are indicated in the figure.
Fig. 3. Measured (symbols) and fitted (solid lines) r(E0,V) curves for Agfa-Gevaert 8E75HD, for phase holograms processed by AAC developer and R-9 bleach. Visibilities are indicated in the figure.
Comparison of the r(DD) characteristics, i.e. the square root of the diffraction efficiency against the amplitude of the density modulation before beaching, provides more information about the various processings since it refers to the conversion of the developed absorption grating into a phase one. The r(DD) characteristics obtained by processing the holograms by the combinations of the AAC developer and the R-10 and R-9 bleaches are shown in Fig. 4. The lines connecting the points serve just to guide the eye. Due to the application of the same developer, the density modulations obtained are the same. The slopes of the rising parts of the r(DD) curves are around 0.22 for the R-10 bleach and around 0.3 for the R-9. This results in lower diffraction efficiencies when using R-10. Besides of the higher slope of the r(DD) curves at each visibility, their quasi-linear range is also larger in case of R-9. The falling part of the r(DD) curve goes the closest to the rising one at about V = 0.4 in case of R-10 bleach and at 0.4 and 0.8 in case of R-9 bleach. To better visualize the differences in the r(DD) characteristics corresponding to the two bleaches, the curves corresponding to visibilities 0.6, 0.8 and 1.0 are shown in common coordinate systems in Figs. 5–7. There are considerable differences in the slopes of the r(D) curves for the two bleaches at visibilities V = 0.6 and 0.8, especially in the lower branch of the curves (i.e. at high exposures), while the two curves are quite close to each other at V = 1.0. The effect of the noise grating in case of the R-10
360
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
Fig. 6. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 0.8. (Compiled from Fig. 4.)
Fig. 7. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 1.0. (Compiled from Fig. 4.)
Fig. 4. Square root of the diffraction efficiency of phase holograms recorded in Agfa-Gevaert 8E75HD plates as a function of the amplitude of the before-bleach optical density modulation. All the holograms were developed by AAC. First column corresponds to R-10 bleach, the second one to R-9. Fringe visibility is indicated on the extreme right of each row. Continuous lines just serve to guide the eye.
bleach can be seen clearly in Fig. 6 around D = 2.25. It can be seen in Fig. 7 that there is a considerable difference in maximum values of r, 0.55 for R-10 and 0.75 for R-9. The corresponding values of the diffraction efficiency are 30% and 56%. It is interesting to note that comparison of another rehalogenating type bleaching agent, EDTA with R-9, using the same developer and recording material as here, led to similar results [24], but differences in the maxima of r were lower. 5. Conclusion
Fig. 5. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 0.6. (Compiled from Fig. 4.)
A systematic study of the effects of a rehalogenating and a solvent bleaching agent and a common developer on the diffraction efficiency of phase holograms recorded in AgfaGevaert 8E75 HD emulsion was performed. Relating the square root of the diffraction efficiency to the pre-bleach optical density modulation (with fringe visibility as parameter) of the recorded holographic gratings allowed a quantitative comparison to be made between the two bleaching agents. The presence of noise gratings manifested itself by pronounced dips in these characteristics. The same latent absorption grating was transformed to a higher efficiency phase grating by using R-9 than R-10 bleach. The results presented in this article can be used either for the optimisa-
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
tion of holographic recording or, using an adequate model, for the determination of the physico-chemical processes that take place during processing of phase holograms. Acknowledgment This work has been funded by the National Research Fund of Hungary (OTKA) under Grant No. T 47265. References [1] H.I. Bjelkhagen, Silver-Halide Recording Materials for Holography and their Processing, Springer, Berlin, 1993. [2] D.H. McMahon, A.R. Franklin, Appl. Opt. 8 (1969) 1927. [3] R.L. van Renesse, F.A.J. Bouts, Optik 38 (1973) 156. [4] A. Schmackpfeffer et al., IBM J. Res. Dev. Sept. 1970 (1970) 533. [5] S. Kumar, K. Singh, Optica Applicata 21 (1991) 49.
[6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
P. Hariharan, Opt. Commun. 3 (1971) 119. J. Crespo et al., Appl. Opt. 25 (1986) 1642. S. Kumar, K. Singh, J. Opt. (India) 19 (1990) 108. R. Kostuk, Proc. SPIE 1212 (1990) 55. R. Kostuk, Appl. Opt. 30 (1991) 1611. D.J. Cooke, A.A. Ward, Appl. Opt. 23 (1984) 934. H. Kiemle, W. Kreiner, Phys. Lett. A 28 (1968) 425. H.T. Buschmann, Optik 34 (1971) 240. P. Hariharan, C.M. Chidley, Appl. Opt. 26 (1987) 1230. P. Hariharan, C.M. Chidley, Appl. Opt. 26 (1987) 3895. P. Hariharan, C.M. Chidley, Appl. Opt. 27 (1988) 3065. P. Hariharan, C.M. Chidley, Appl. Opt. 27 (1988) 3852. I. Ba´nya´sz et al., Opt. Commun. 111 (1994) 225. I. Ba´nya´sz et al., J. Mod. Opt. 45 (1998) 881. I. Ba´nya´sz, Opt. Lett. 18 (1993) 658. L. Solymar, G.D.G. Riddy, J. Opt. Soc. Am. A 7 (1990) 2107. A. Fimia et al., Opt. Lett. 19 (1994) 1243. A. Fimia et al., Opt. Eng. 34 (1995) 1108. I. Ba´nya´sz et al., J. Mod. Opt. 46 (1999) 591.
361
Comparison of the effects of two bleaching agents on the recording of phase holograms in silver halide emulsions I. Ba´nya´sz
*
Department of Crystal Physics, Research Institute for Solid State Physics, P.O. Box 49, H-525 Budapest, Hungary Received 8 April 2006; received in revised form 20 June 2006; accepted 21 June 2006
Abstract Optical densities before bleaching and final Lin-curves of plane-wave phase holograms recorded in Agfa-Gevaert 8E75HD emulsions were determined for combinations of the AAC developer with a solvent bleach (R-9) and a (fixation-free) rehalogenating bleach (R-10). To characterize the processing, the square root of the diffraction efficiency of the processed holograms was related to the amplitude of the optical density modulation obtained at the development step. Sensitivity, linearity and dynamic range of the processes could thereby be compared directly. 2006 Elsevier B.V. All rights reserved. PACS: 42.40.i; 42.40.Eq; 42.40.Ht; 42.40.Lx; 42.70.Ln Keywords: Holography; Theory of holography; Photographic and recording problems; Holographic instrumentation and techniques; Light sensitive materials
1. Introduction A detailed description of holographic bleaching techniques can be found in the monograph of Bjelkhagen [1]. They can be divided into three main categories: conventional or direct (rehalogenating) bleaching, fixation-free rehalogenating bleaching and reversal (complementary) or solvent bleaching. In conventional bleaching the silver grains are converted into a transparent silver salt after fixation, i.e. the removal of the unexposed silver-halide crystals. In fixation-free rehalogenating bleaching the conversion takes place without a fixation step, so that the unexposed silver-halide crystals remain in the emulsion. In reversal bleaching the developed silver grains are converted into a water-soluble silver complex, which is removed from the emulsion during bleaching, leaving the original, unexposed silver-halide grains in the emulsion. Obviously, there is no fixation step before the reversal bleaching, as otherwise all *
Tel.: +36 702988539/13922222x1732; fax: +36 13922215. E-mail address: [email protected].
0030-4018/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2006.06.061
the unexposed and exposed silver halide grains would disappear after bleaching. Due to the considerable material removal in both conventional and reversal bleaching, the thickness of the emulsion is reduced. Fixation-free rehalogenating bleaching does not lead to emulsion shrinkage. One of the first rehalogenating bleaches used in holography was Kodak R-10, as modified by McMahon and Franklin [2], applied after a fixation step. Van Renesse and Bouts wrote an excellent study of the various bleaching agents used in holography [3]. One of the bleaches used in those experiments was also a version of Kodak R-10 (with fixing). They came to the conclusion that phase variations in the bleached holographic emulsions were determined by the electric polarizability and volume of the molecules of the silver compound formed. Schmackpfeffer et al. [4] studied the optimisation of the generation of high-efficiency holographic gratings in bleached silver halide emulsions. They recorded phase holograms in Agfa 8E70 emulsions, using Kodak HRP developer, fixed in Agfa G334, and bleached with either R-10 or Kodak EB-2 bleaches. They
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
found that Kodak R-10 bleach resulted in the highest diffraction efficiencies. Kumar and Singh [5] also used a modified version of R-10, with a fixation step, along with four other bleaching agents, to try to improve the diffraction efficiency of phase holograms recorded in Agfa-Gevaert 8E75 HD emulsions. They found that bleaching agent R-10 gave the highest diffraction efficiencies over a wide range of bias exposures, together with ferric chloride bleach. As for scattering, R-10 produced somewhat lower levels than the ferric chloride bleach at higher exposures. The fixation-free version of rehalogenating processing was discovered by Hariharan [6]. Crespo et al. [7] recorded high-efficiency (up to 70%) reflection gratings in AgfaGevaert 8E75 HD plates with fixation-free rehalogenating bleaching, using various bleaching agents, including R-10. They too found that it was R-10, which resulted in the highest diffraction efficiencies and lowest scattering. Kumar and Singh [8] obtained holograms with diffraction efficiencies up to 87% at a wavelength of 442 nm in Kodak 649F emulsions, using D-19 developer and a slightly modified R-10 bleach, without a fixation step. Kostuk [9,10] applied a factorial optimisation for the constituents of the R-10 bleach. He recorded reflection gratings in Agfa-Gevaert 8E75 HD and Ilford SP673 emulsions, using a variant of the CW-C1 developer [11] and the modified R-10 bleach, without fixing. He concluded that the best composition of R-10 had a high concentration of rehalogenating agent (KBr) and low concentration of oxidizer and sulphuric acid. It was Kiemle and Kreiner [12] who first applied reversal bleaching to holography. Buschmann [13] studied three bleaching processes, including R-9, with and without fixation step in Agfa-Gevaert 8E75 holographic emulsions at a wavelength of 647 nm, at a spatial frequency of 1545 lp/mm. He related the diffraction efficiency of the final phase gratings to the pre-bleach optical density of the initial absorption gratings. According to his results, R-9 with a previous fixation step gave somewhat higher efficiencies than without fixation, but that processing also resulted in considerably higher (some 2.0 dB) scattering. Hariharan and Chidley published a series of papers on the effects of bleaching agents on the diffraction efficiency and signalto-noise ratio of phase holograms. In the first [14] they recorded plane-wave phase holograms in Agfa-Gevaert 8E75 HD plates at a wavelength of 632.8 nm and interbeam angle of 45. They compared the diffraction efficiencies and scatterings of the holograms obtained using the combinations of a conventional bleach and the R-9 reversal bleach with 5 different developers, with (in case of conventional bleach) and without (in case of R-9) fixing. They found that solution physical development and local hardening of the gelatine during development were the main causes of the considerable differences in diffraction efficiencies and scatterings obtained. In another paper [15] they studied the effects of the type and concentration of the halide used in the rehalogenating bleaches on diffraction efficiency and scattering. They obtained the best results
357
with low concentrations of KI as a rehalogenating agent. The same authors also studied the effects of conventional and rehalogenating bleaches as functions of the spatial frequency of the holographic gratings [16,17]. In spite of the very considerable literature of the field, of which some representative examples were enumerated above, our knowledge about bleached phase holograms is still far from being complete. For example, all the work mentioned above lacks a study of the dependence of the effects of processing on the visibility of the constructing interference pattern; the authors recorded the holograms over a range of bias exposures, but only for a fixed fringe visibility (usually at V = 1.0). However, it is the illumination difference between dark and bright fringes that drives the physical and chemical processes that take place at the development step, and, indirectly, those taking place during bleaching. The author of the present paper and his co-authors extended the study of the processing of both amplitude [18] and phase [19] holograms to the whole range of visibilities of the recording interference patterns. The present work deals with the comparison of the effects of fixation-free rehalogenating and solvent bleaching on the diffraction efficiency of holographic gratings recorded in Agfa-Gevaert 8E75 HD plates over a wide range of bias exposures and fringe visibilities. 2. Experimental procedure Plane wave holograms were recorded on Agfa-Gevaert 8E75HD NAH emulsions on rectangular glass substrates with dimensions of 64 mm · 64 mm · 1.5 mm. A helium– neon laser operating at 632.8 nm was used for recording and reconstruction. The interbeam angle was 45, thus the spatial frequency of the gratings was about 1200 line pairs/mm. For each processing combination, hologram pairs at seven values of fringe visibility, namely at V = 0.2, 0.4, 0.6, 0.8, 0.9, 0.95 and 1.0 were recorded. The corresponding beam ratios were determined from the following equation: pffiffiffi 2 R V ¼ ð1Þ Rþ1 where V is the visibility of the interference fringes and R is the ratio of the intensities of the two beams. The beam ratios were set by adjusting a variable beam splitter and inserting appropriate neutral density filters in the unexpanded object beam. Twelve hologram pairs at exposures ranging from 10 lJ/cm2 to 1.6 mJ/cm2 were recorded at each visibility. The total intensity at recording was maintained constant at 400 lW/cm2 ± 1% throughout the experiments. The first element of each hologram pair was developed and fixed to obtain an absorption hologram and the second was developed with the same developer and bleached, without a fixation step. The AAC developer, the composition of which is given in Table 1, was used throughout, at temperature T = 20 C. All the absorption holograms were fixed in Kodak F24 fixer for 5 min. Bleach-
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
358 Table 1 Composition and use of the AAC developer Name of the compound
Quantity
Ascorbic acid Sodium carbonate Distilled water
18 g 120 g 1l
Developing time Temperature
3 min 20 C
Table 2 Composition of the R-10 and R-9 bleaches Name of the compound
Name of the bleach R-10
R-9
Potassium bromide Potassium dichromate Sulphuric acid (cc.) Distilled water
35 g 2g 10 ml 1l
– 2g 10 ml 1l
ing was also performed at 20 C, and terminated 1 min after the plate became transparent. The composition of R-10 and R-9 bleaches is shown in Table 2. These experiments allowed us to compare the effects of two different bleaches (R-10 and R-9) used with the same developer (AAC). For both bleaches, all the holograms were processed simultaneously. After processing, the optical density of the absorption holograms and the diffraction efficiency of the phase holograms were measured. Care was taken to minimise the effects of stray light. When measuring low intensities (efficiencies below 0.1% and optical densities above 3) the detector was enclosed in a black box that admitted only light coming directly from the hologram, and the intensity of stray light was always checked. Both the optical density and the diffraction efficiency were corrected for reflection losses. In the case of the optical density measurements the intensity of the reflected beam was also measured and subtracted from that of the incident beam. In the diffraction efficiency measurements reflection losses were calculated from the Fresnel-formula instead of measuring the reflected intensity, because the latter proved to be uncertain due to the presence of interference fringes.
is the optical density, E0 is the bias exposure, and t0, E1, j and t1 are fit parameters. The square root of the diffraction efficiency against bias exposure and fringe visibility was fitted by the function [20] rðE0 ; V Þ ¼ f ðE0 Þð1 eV Þe
½V V 0 ðE0 Þ2 w2 ðE0 Þ
ð3Þ
where r is the square root of the diffraction efficiency, E0 is the bias exposure, V is the visibility of the interference fringes and f(E0), V0(E0) and w(E0) are parameter functions of the following form: 2 3 1 ParðE0 Þ ¼ ci01 4 þ ci13 5 E0 exp ci11ci12 þ1 2 3 1 4 þ ci23 5 i21 exp E0cc þ 1 i22 2 3 1 4 ð4Þ þ ci33 5 E0 exp ci31ci32 þ1 where ‘‘Par’’ stands for f, V0 and w, and cixx represents three sets of constants (i = f, V0, w). If E0 is the bias exposure and V the fringe visibility, the minimum (Emin) and maximum (Emax) exposures can be expressed as follows: Emin ¼ E0 ð1 V Þ
ð5Þ
Emax ¼ E0 ð1 þ V Þ
ð6Þ
Consequently, the amplitude of the density modulation at a bias exposure of E0 and visibility of V is: DDðE0 Þ ¼ DðE0 ð1 þ V ÞÞ DðE0 ð1 V ÞÞ
ð7Þ
This expression was used for the calculation of DD from the values of D obtained by fitting Eq. (2) to the experimental data. 4. Results and discussion An example of a D(E0) function fitted to measured data is shown in Fig. 1. The absorption holograms were devel-
3. Model functions The results of the measurements, optical density as a function of exposure and square root of diffraction efficiency as a function of bias exposure and interference fringe visibility, were fitted by analytical functions. The latter functions are also called as Lin-functions or Lin-curves after the name of the researcher who introduced them. The density against exposure curves were fitted by the following function [18]: where D 2 3 t0 6 DðE0 Þ ¼ 2 log 4 j E1 E0
þ1
7 þ t1 5
ð2Þ
Fig. 1. Measured (points) and fitted (solid line) D(E) function for AgfaGevaert 8E75HD, for phase holograms recorded at a fringe visibility of 0.2, and developed by AAC.
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
oped by AAC and fixed by Kodak F24, at V = 0.2. The parameters of the fitted function are t0 = 0.75, E1 = 37.5 lJ/cm2, j = 2.15 and t1 = 0.0075. r(E0, V) functions fitted to experimental data corresponding to the two bleaches are shown in Figs. 2 and 3. Parameters of the r(E0, V) function of the combination of AAC and R-10 are shown in Table 3. The parameters corresponding to the combination of AAC and R-9 can be seen in Table 4. The model is generally in good agreement with the measurements. However, large differences can be found in the case of the rehalogenating bleach (R-10), especially at visibilities V = 0.8 and 1.0 at high exposures (between E0 = 100 and 400 lJ/cm2). The strong dip in r can be attributed to the presence of noise gratings [21–23]. For this reason we used the measured values of r instead of the fitted ones to prepare the r(DD) characteristics. If we compare the above Lin curves, we can see that it is R-9, which gives higher diffraction efficiency, while the combination of AAC with R-10 reaches peak diffraction efficiency at a lower exposure. However, these characteristics provide no direct information on the mechanism of hologram formation.
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Table 3 Parameters of the r(E0, V) function of Agfa 8E75HD Indices (xx)
cfxx
cðV 0 Þxx
cwxx
01 11 12 13 21 22 23 31 32 33
1.5 42 21 0 280 140 0 11.5 3.0 0
4.0 170 75.0 0.3 20.0 11.0 0.49 70 8.0 0.35
4.0 190.0 75.0 0.3 25.0 8.0 0.49 60 8.0 0.4
Developer: AAC, bleach: R-10.
Table 4 Parameters of the r(E0, V) function of Agfa 8E75HD Indices (xx)
cfxx
cðV 0 Þxx
cwxx
01 11 12 13 21 22 23 31 32 33
1.5 38 32 0 675 300 0 12.5 3.2 0
3.0 72 2.5 0.21 53.5 2.8 0.15 28 1.8 1.64
3.0 20.5 3.0 0.95 700 120 0.27 4 21 0.14
Developer: AAC, bleach: R-9.
Fig. 2. Measured (symbols) and fitted (solid lines) r(E0,V) curves for Agfa-Gevaert 8E75HD, for phase holograms processed by AAC developer and R-10 bleach. Visibilities are indicated in the figure.
Fig. 3. Measured (symbols) and fitted (solid lines) r(E0,V) curves for Agfa-Gevaert 8E75HD, for phase holograms processed by AAC developer and R-9 bleach. Visibilities are indicated in the figure.
Comparison of the r(DD) characteristics, i.e. the square root of the diffraction efficiency against the amplitude of the density modulation before beaching, provides more information about the various processings since it refers to the conversion of the developed absorption grating into a phase one. The r(DD) characteristics obtained by processing the holograms by the combinations of the AAC developer and the R-10 and R-9 bleaches are shown in Fig. 4. The lines connecting the points serve just to guide the eye. Due to the application of the same developer, the density modulations obtained are the same. The slopes of the rising parts of the r(DD) curves are around 0.22 for the R-10 bleach and around 0.3 for the R-9. This results in lower diffraction efficiencies when using R-10. Besides of the higher slope of the r(DD) curves at each visibility, their quasi-linear range is also larger in case of R-9. The falling part of the r(DD) curve goes the closest to the rising one at about V = 0.4 in case of R-10 bleach and at 0.4 and 0.8 in case of R-9 bleach. To better visualize the differences in the r(DD) characteristics corresponding to the two bleaches, the curves corresponding to visibilities 0.6, 0.8 and 1.0 are shown in common coordinate systems in Figs. 5–7. There are considerable differences in the slopes of the r(D) curves for the two bleaches at visibilities V = 0.6 and 0.8, especially in the lower branch of the curves (i.e. at high exposures), while the two curves are quite close to each other at V = 1.0. The effect of the noise grating in case of the R-10
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I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
Fig. 6. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 0.8. (Compiled from Fig. 4.)
Fig. 7. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 1.0. (Compiled from Fig. 4.)
Fig. 4. Square root of the diffraction efficiency of phase holograms recorded in Agfa-Gevaert 8E75HD plates as a function of the amplitude of the before-bleach optical density modulation. All the holograms were developed by AAC. First column corresponds to R-10 bleach, the second one to R-9. Fringe visibility is indicated on the extreme right of each row. Continuous lines just serve to guide the eye.
bleach can be seen clearly in Fig. 6 around D = 2.25. It can be seen in Fig. 7 that there is a considerable difference in maximum values of r, 0.55 for R-10 and 0.75 for R-9. The corresponding values of the diffraction efficiency are 30% and 56%. It is interesting to note that comparison of another rehalogenating type bleaching agent, EDTA with R-9, using the same developer and recording material as here, led to similar results [24], but differences in the maxima of r were lower. 5. Conclusion
Fig. 5. Comparison of the r(DD) characteristics of holograms processed with AAC developer and R-10 (triangles) and R-9 (squares) bleaches. Visibility is 0.6. (Compiled from Fig. 4.)
A systematic study of the effects of a rehalogenating and a solvent bleaching agent and a common developer on the diffraction efficiency of phase holograms recorded in AgfaGevaert 8E75 HD emulsion was performed. Relating the square root of the diffraction efficiency to the pre-bleach optical density modulation (with fringe visibility as parameter) of the recorded holographic gratings allowed a quantitative comparison to be made between the two bleaching agents. The presence of noise gratings manifested itself by pronounced dips in these characteristics. The same latent absorption grating was transformed to a higher efficiency phase grating by using R-9 than R-10 bleach. The results presented in this article can be used either for the optimisa-
I. Ba´nya´sz / Optics Communications 267 (2006) 356–361
tion of holographic recording or, using an adequate model, for the determination of the physico-chemical processes that take place during processing of phase holograms. Acknowledgment This work has been funded by the National Research Fund of Hungary (OTKA) under Grant No. T 47265. References [1] H.I. Bjelkhagen, Silver-Halide Recording Materials for Holography and their Processing, Springer, Berlin, 1993. [2] D.H. McMahon, A.R. Franklin, Appl. Opt. 8 (1969) 1927. [3] R.L. van Renesse, F.A.J. Bouts, Optik 38 (1973) 156. [4] A. Schmackpfeffer et al., IBM J. Res. Dev. Sept. 1970 (1970) 533. [5] S. Kumar, K. Singh, Optica Applicata 21 (1991) 49.
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