Holographic Photopolymers

Therefore, the diffraction efficiency of transmission holography is decreased. The maximum diffraction efficiency of transmission holography is 6.25%. Since the component of and 1, is negligibly small, the refraction efficiency of reflection holography is higher. The theoretical maximum diffraction efficiency of phase holography is estimated to be 34%, and that of reflection efficiency 100%. Theoretical and diffraction efficiencies of various types of holography are shown in Table 5.2. 

Silver halide is a general recording material for holography. Two-dimensional, three-dimensional, phase, and transmission are applied for holography. Gelatin emulsion of silver halide is coated on glass. Holographic 

Hologram Maximum Diffraction Efficiency % theoretical Experimental Recording Materials 

Black silver is converted to transparent silver by bleaching in phase holography. The SD-48 developing method is relief imaging by silver halide. 

Dichromated gelatin sensitized by methylene blue is sensitive to 400 to 700 nm. Therefore, three laser lights, red, green, and blue, can be exposed to dichromated gelatin sensitized by methylene blue. Full-color holography is thus performed by dichromated gelatin. 

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Gallego S., Ortuno M., Neipp C., Marquez A., Belendez A., Pascual I., Kelly J. Sheridan J. (2005). 3 Dimensional analysis of holographic photopolymers based memories. Optics express, Vol. 13, No. 9, 3543-3557. 

Stabilized radicals, and so on [1]. An unprecedented example is the in situ observation of a light-induced radical pair produced in a crystal of 2,2 -di (p-chlorophenyl)-A,A, 5,5 -tetraphenyl-biimidazole (o-Cl-HABI) by X-ray diffraction, as shown in Scheme 7.1 [2], HABl derivatives are well known as the photo- and thermochromic compounds, the polymerization photo-initiators in imaging materials, and holographic photopolymers since it was prepared in 1960 [3-5], It has been proposed that the photolysis of the H ABI derivatives in benzene solution instantaneously produces a pair of lophyl (triarylimidazoyl) radicals. The lophyl radical has been proposed to be an initiator for the radical polymerization. Despite the intriguing properties of HABI derivatives, there is very few report [6]. 

KEL 05b] Kelly J.V., O Neill F.T., Sheridan J.T. et al, Holographic photopolymer materials nonlocal polymerization-driven diEfusion under nonideal kinetic conditions , Journal of the Optical Society of America B, vol. 22, pp. 407-416, 2005. 

Researchers at DuPont reasoned that differences in refractive index could be created on a submicron scale in dry photopolymer films, that such refractive index differences could function as diffraction gratings, and that lasers could be used to produce these structures. In initial experiments, photopolymers were exposed using lasers beams diffracted by commercial gratings, and polymerized structures in exposed photopolymers confirmed that very high spatial resolution was possible [2]. This work led to the development and commercialization of holographic photopolymer film from DuPont. 

Bis-imidazole photoinitiators are well-suited to photopolymer holographic films because these photoinitiators are sensitive, can be stored indefinitely, can be sensitized to all visible wavelengths, and are readily compatible with binder systems. It was the coincident development of bis-imidazole photoinitiators which catalyzed the rapid growth of photopolymer films in DuPont, holographic films in particular. The ready sensitization of bis-inudazoles has been exploited in a wide variety of holographic photopolymer films sensitized to all major visible commercial lasers, including panchromatic sensitization for the production of fiill-color... 

Photopolymers and photothermoplasts are mentioned only in connection with holographic data storage (see Holography). The classical method of optical data storage in silver haUde films (photographic film, microfiche technique) is not discussed (see Photography). 

Materials. For holographic information storage, materials are required which alter their index of refraction locally by spotwise illumination with light. Suitable are photorefractive inorganic crystals, eg, LiNbO, BaTiO, LiTaO, and Bq2 i02Q. Also suitable are photorefractive ferroelectric polymers like poly(vinyhdene fluoride-i o-trifluorethylene) (PVDF/TFE). Preferably transparent polymers are used which contain approximately 10% of monomeric material (so-called photopolymers, photothermoplasts). These polymers additionally contain different initiators, photoinitiators, and photosensitizers. 

AH attempts to develop photopolymers or photothermoplasts suitable for fast and reversible recording and read-out of volume-phase holograms, however, have not gained commercial appHcation. The most important characteristics of materials for holographic information recording are Hsted in Table 4 (158). 

Systems have now been commercialised, based on holographic elements produced using photopolymers, which utilise wavelength selectivity and controlled spectral bandwidth to use and control the incident light. °... 

In the holographic scanner a series of phase holograms is recorded in a photopolymer film on a glass cylinder (Fig. 7). When the cylinder is rotated, the holograms cause an input beam to scan in the same way as a multifaceted prism would. However, because of the cylindrical symmetry of the device, it does not distort, even at high rotation rates. In addition, the holograms serve as lenses to focus the beam. The output beam quality is sufficient to resolve 1917 spots per scanning line at a rate of 7.76 x 10 spots per second (11). 

Figure 18. Spatial frequency response of a photopolymer (37). The response is measured in terms of the efficiencies of holographic gratings. For the solid curve each efficiency was measured with the sample immersed in an index-matching fluid, so as to eliminate the effects of any modulation of the sample thickness. For the dashed curve the sample was in air. The curves show that for spatial frequencies >100 lines/mm the response of the material is almost entirely a refractive index modulation, while for <100 lines/mm there is little index modulation but there is a substantial thickness modulation.

Various photopolymer systems have also been developed for analog as well as digital holographic memories and photoresists (see Refs. [7, 8] for details). 

L.V. Natarajan, R.L. Sutherland, V. Ton-diglia, T. J. Bunning, W. W. Adams, Photopolymer Materials, Development of Holographic Gratings, in J. C. Salamone (ed.), Concise Polymeric Materials Encyclopedia, CRC Press, Boca Raton, Florida, USA (1999), p. 1052. 

A photopolymer is sandwiched between two glass plates. After holographic exposure, monomes are polymerized at interference fringe the difference in the refractive index between the polymerized part and the monomer part causes a holographic phase shift. Then holographic recording is possible by the photopolymer. 

Nussbaumer, (2005) "Ti02 Nanoparticle-Photopolymer Composites for Volume Holographic Recording." Adv. Fund. Mater., 15,1623-1629. 

S. Martin, P. Leclere, Y. Renotte, V. Toal, Y. Lion, (1995) "Characterisation of an acrylamide-based dry photopolymer holographic recording material." Opt Eng., 33,3942-3946. 

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