Introduction to the hottest color holographic reco

2022-08-18
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Introduction to color holographic recording materials (2)

2. Dichromate gelatin

dichromate gelatin is a good phase recording medium, and its resolution can reach 5000 lines/mm. Dichromated gelatin has the advantages of high diffraction efficiency and high signal-to-noise ratio. The disadvantage is low sensitivity, only (3 ~ 7) j/cm2, which is about one millionth of Kodak 649f. Dichromate gelatin is sensitive to temperature and bacteria, and is sensitive to the temperature and humidity of the environment. It is afraid of humidity. The image is not 4. The projector needs to be kept away from heat sources It is stable and easy to eliminate images, so it should be stored in a closed container. Chromium is poisonous to people

the refractive index of the hardened gelatin of dichromate gelatin can reach 0.08, which is used to record the - H curve of volume holography. Gelatin has two kinds of hardening and non hardening. Unhardened gelatin can be used to make relief holograms; Hardened gelatin is suitable for making refractive phase holograms. Because the part of this material irradiated by light is not black and does not absorb light during hologram reconstruction, its diffraction rate is high, and the diffraction efficiency of the volume hologram made with it can reach 90%

dichromate gelatin and other dichromate colloids are the earliest photographic materials. Gelatin is extracted from the natural protein bone glue of animals. After gelatin is mixed with a small amount of dichromate for sensitization, it is irradiated with short wavelength blue violet light, and the exposed place becomes hard, which is less soluble in water than the unexposed place. After washing, it can be changed into thickness, density or both. Therefore, it can be used as holographic material to produce a phase hologram modulated by thickness or refractive index. The wavelength of dichromate gelatin absorption zone is about 540nm, so it can only be used for FRP/elastic element fatigue life testing machine technical parameters: 514.5nm and 488nm of argon ion laser, or 412nm wavelength of helium cadmium laser. Because the dichromate gelatin dry plate, unlike the silver halide dry plate, has tiny silver particles, its resolution is very high, up to 2000 ~ 5000 lines/mm

if the 632.8nm wavelength of He Ne laser is used, other sensitizing dyes must be added to gelatin. The commonly used dyes are methylene blue and methylene green

3. photoresist

photoresist is a photosensitive organic recording material suitable for recording thin relief phase holograms. This material can be exposed and developed to form relief images. It has two types: positive type and negative type

positive photoresist, the exposed place absorbs light to produce organic acids, which are destroyed and crosslinked to become soluble organic materials, which are dissolved by development; Negative photoresist, the exposed place, due to the absorption of light in the intermolecular shape, the metal price continued to be depressed in 2013, which made the organic material harden and become insoluble. After development, only the unexposed part was dissolved, leaving the hologram of the uneven surface. As a holographic recording material, photoresist can be used to integrate the long material of more than 10mm and the cable wire sample of less than 10mm by centrifugal glue throwing to make a micron scale film. The shrinkage and deformation are very small, and the diffraction efficiency is high. It is a good material for making relief hologram, and the resolution can reach about 3000 lines/mm. However, there are two shortcomings in using it as relief holographic material. One is low sensitivity; The second is the narrow spectral response range. Photoresists are sensitive to blue light and are usually exposed with 441.6nm wavelength of he CD laser. Photoresist is used to record holograms, which requires that it must be well bonded to the substrate. Therefore, only positive photoresist can be selected

photoresist can produce a strong acid under the action of light, and the main resin can undergo photodegradation and photocrosslinking reaction by heating. Because the strong acid produced can be recycled, high sensitivity can be obtained. At present, the widely used photoacid generator is Euonymus salt, such as iodeuonymus salt, thioeuonymus salt, iron Euonymus salt, carbon Euonymus salt, etc. For example, the photosensitive system composed of cresol resin - tert butyl naphthenate - triphenylthiohexafluorophosphor euonyl salt is a positive photoresist, with a photosensitive sensitivity of several mj/cm2

abroad, Shipley's microposit-1350 (az-1350) positive photoresist is widely used. There is BP-212 positive photoresist produced by Beijing No.2 Chemical Plant in China

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