Recording system adjustment
(1) Adjust each optical element in the optical path so that the optical path lengths of the object light and reference light from the beam splitter to the dry plate are as equal as possible (the maximum optical path difference should be within the coherence length of the laser used). The intersection angle of the object light and the reference light should not be too large, the maximum is 60 ° ~ 90 °, the illuminated object should be able to be effectively illuminated by light.
(2) Adjust the optical path so that the object light can reach the dry plate effectively, and make the optical path convenient for adjusting the beam balance later. Use an optical power meter to measure the intensity ratio of the object light and the reference light at the dry plate position, and adjust the beam splitter so that the intensity ratio of the two reaches the specified value according to the size and type of the object to be photographed (for example, when shooting a two-dimensional reflection hologram , The intensity ratio is 1: 1 ~ 3: 1) in order to determine the exposure time (for two-dimensional transmission hologram, the intensity ratio is 2: 1 ~ 10: 1).
(3) Due to the vibration of the shutter when it is opened and closed, it is often transmitted to the recording hologram table. Therefore, the shutter should be separated from the plane of the recording hologram table, installed separately or covered with a rubber pad on the recording platform, and the shutter should be fixed on it to reduce vibration.
Determine exposure time
The method to determine the exposure time is to first determine the exposure according to the sensitivity of the dry plate and conduct a preliminary experiment. As shown in Figure 10-55, on a dry plate, the exposure time is divided into several exposures at intervals of 1 to 2s, and then the dry plate is developed. Choose the appropriate exposure time from the results.
During the exposure, after mounting the dry plate on the dry plate frame, due to slight vibration, wait 30 minutes before opening the exposure shutter for exposure. When the operator is operating, do not move the body and gasp so as to avoid air vibration.
Fixing of amplitude hologram
The coating of the holographic dry plate is silver halide latex. During exposure, the metal silver ion Ag + and the halogen element ion Br- are decomposed. Due to the photoelectric effect, the electron e- is knocked out, and the electron e- is neutralized with the metal silver ion to generate metal silver The particles are dispersed in latex. The amount of silver particles forms a latent image with increasing exposure. Through development, the place containing the precipitated silver becomes a reduction center, and a large amount of silver bromide is reduced to metallic silver. Since silver particles with different densities absorb light differently, an image is formed. The role of fixing is to remove the unexposed silver halide in the latex and the remaining silver halide in the exposed part. In this way, after exposure, the holographic dry plate is subjected to development and fixing processes to obtain an amplitude hologram.
The most commonly used developer in the holographic process is Kodak D-19, and the fixing solution is F-5. The operation process is as follows:
â‘ Development According to the type and development time of the developer on the dry plate, under the safety lamp, all the exposed dry plates are quickly immersed in the D-19 developer, with the latex facing upward, and the developer is stirred for about 2min , Optical density is about 0.5 ~ 0.7, take out and wash for 30s.
â‘¡ Stop the display and soak it in SB-1 stop liquid for 30s, and take out the water for 30s.
â‘¢ When fixing, it does not need to be carried out under the safety light. Can be operated under conventional lighting. Immerse in the fixing solution F-5 for 3 to 5 minutes. Stir the fixing solution during the fixing process, during which the photoresist will gradually become transparent. After the dry plate is completely transparent, the fixing should be continued, which is about twice as long as the dry plate is put into the fixing solution until it becomes transparent. When using hard film fixer, it is best to soak for 10 ~ 20min.
â‘£ Rinse in running water for 5 minutes. When washing, pay attention to the water flow to ensure that the dry plates do not overlap to avoid marks on the dry plates. The water temperature of the water flow is not higher than 25oC to prevent the photosensitive film from falling off.
⑤ Remove the sensitizer and soak in methanol or absolute ethanol for 3 minutes.
â‘¥Dry out and dry naturally. If the sensitizer is not removed, it should be washed with distilled water to avoid the contamination of the tap water impurities.
For continuous laser recording, the desensitized latex formulated with 600 mL of phenol safflower red and 1 L of methanol instead of the fixing solution for 3 minutes can improve the quality of the hologram.
Phase hologram development and fixing process
The hologram produced by the holographic dry plate is bleached to obtain a phase hologram. There are two types of phase holograms: relief (thickness modulation) and refractive index modulation. The phase holography of the holographic dry plate after bleaching is mainly based on refractive index modulation with a fixed relief.
There are many types of bleaching, which can be roughly divided into three categories: ordinary bleaching, non-fixing bleaching, and bleaching after fixing.
â‘ Common bleaching The main procedure of common bleaching is to develop and fix the amplitude hologram formed by bleaching, and then bleach to form a phase-type hologram. After bleaching, the metallic silver forms a transparent silver salt. The refractive index of the silver salt is greater than that of gelatin, so that the refractive index modulation occurs, which can be illustrated with FIG. 1. (A) indicates that after exposure, the exposed part of the gelatin contains metallic silver particles through development and fixing; (b) indicates that after bleaching, the silver particles in the exposed part become transparent silver salts (c) indicates the exposed part during drying The surface of the gelatin is deformed due to tanning, forming a surface relief. When the spatial frequency of the hologram is less than 200 lines / mm, the relief is more obvious; when the spatial frequency is larger, the relief is very small. In addition, the relief modulation and refractive index modulation are additive.
The normal bleaching procedure is the same as the amplitude hologram, except that a bleaching procedure and water washing are added after fixing and washing. The bleaching time is generally extended by the same time after rinsing. Changing the subsequent processing can improve the diffraction efficiency.
The processing procedure to improve diffraction efficiency is:
(a) Development D19 developer solution is diluted 1:10 and developed for 2min, washed with water for 30s;
(b) Stop displaying after using SB-1 to stop displaying for 30s, then wash for 30s;
(c) After fixing with F-24 fixing, rinse with running water for 1min;
(d) Bleaching with acid iron bleach after washing in flowing water for 1 min;
(e) Hardening the membrane with alkaline formaldehyde through the hardening fluid and hardening the membrane for 2 minutes and washing with running water for 5 minutes
(f) Swelling and soak in warm water at about 35oC for 10 minutes;
(g) Dehydration is first soaked in 50% isopropyl alcohol for 32 minutes, and then soaked in 100% isopropyl alcohol for 4 minutes;
(h) Drying After removing the dry plate, blow it with hot air immediately, and then blow it with cold wind (to prevent frosting).
Figure 1 Schematic diagram of ordinary bleaching Figure 2 Schematic diagram of reverse bleaching
â‘¡There are two types of unfixed bleaching, one is reverse bleaching, and the other is rehalogenated bleaching.
The process of reverse bleaching without fixing is shown in Figure 2. (A) in the figure shows that after exposure and development, the exposed part in the latex is metallic silver, and the unexposed part is silver halide. (B) indicates that the metallic silver becomes a soluble silver salt during bleaching, which can be removed from the latex, and the unexposed part is still silver halide. This is just the opposite of ordinary bleaching, so it is called reverse bleaching. (C) Relief caused by surface deformation caused by gelatin tanning during exposure. In this case, the effects of surface relief modulation and refractive index modulation are mutually exclusive. The non-fixing bleaching treatment procedure is as follows:
(a) Development with SD-48 for 5min, 24oC, and water washing for 30s;
(b) Stop display, use SB-1 of 21 ～ 27oC to stop display for 30s, and wash for 1min under running water;
(c) Bleaching with R-9 at 21 ～ 27oC for 3min, washing with running water for 5min;
(d) Decolorization: use 21 ～ 27oC S-13A liquid for 1min;
(e) Cleaning: Use S-13B solution of 21 ～ 27oC for 1min, and wash with running water for 5 ～ 10min;
(f) Soak in 50% methanol for 3 minutes for dehydration, and then soak in 100% isopropyl alcohol for 4 minutes;
(g) Drying: Dry naturally at room temperature.
Bleaching fluids without fixing rehalogenation bleach contain alkali metal compounds, such as potassium bromide. It can make the developed metallic silver into silver bromide. The phase modulation is formed because the unexposed part of the silver halide diffuses to the exposed part. The advantage of this bleaching method is that the change in the latex layer is minimal.
â‘¢ Bleaching after fixing Bleaching after fixing utilizes the sensitivity of silver halide latex. After processing, a hologram with the same properties (high diffraction efficiency, low noise) as dichromate gelatin (DCG) is obtained, so it is also called Silver halide-sensitized gelatin hologram (SHSG). This bleaching procedure is:
(a) D-1 developing solution for development, 5mins, 20oC, water washing for 30s;
(b) Stop display, use SB-1 stop display, 30s, wash with running water for 1min;
(c) R-9 reverse bleaching for bleaching, 3min, washing with running water for 10min;
(d) Cleaning with S-13, B liquid, 1min, washing with running water for 5min;
(e) Fixing with F-24 fixation for 3min, washing with running water for 5min;
(f) Soak with distilled water for 2min;
(g) Soak in 50% isopropyl alcohol for 3 minutes, and then soak in 100% isopropyl alcohol for 4 minutes;
(h) Drying: First dry at room temperature for 30 minutes, then put in a desiccator with calcium chloride for 15 hours.
The procedure for fixing after ordinary bleaching is:
(a) DK-20 is used for development for 4 minutes, and rinsed under running water for 1 minute;
(b) Tanning or non-tanning bleaching for bleaching. Wash for 1min after bleaching;
(c) Fixing with F-24 fixing, 3min, washing with running water for 5min;
(d) Swelling and soak in 35oC distilled water for 10 minutes;
(e) Dehydration, soak in absolute ethanol for 2 minutes, and then soak in isopropyl alcohol for 4 minutes;
(f) Drying Drying under 20 <50% RH.
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