Methylene-blue-sensitized gelatin holograms.

Like dichromated gelatin ~DCG!, methylene-bluesensitized gelatin ~MBG! is also a potential holographic recording material1,2 and can be used in forming a hologram with a high diffraction efficiency ~DE! and high signal-to-noise ratio ~SNR!. The addition of methylene blue ~MB! into a gelatin or DCG film renders it effective to record holograms with red light from an inexpensive He–Ne laser, which is the laser most readily available. Two decades of research and development since the first proposal of the use of MB by A. Graube3 has firmly established its status in holographic recording materials, especially when tetramethylguanidine ~TMG!, used as an efficient electron donor for its improved photosensitivity, was found by J. Blyth.4 Solano et al.5 first used a simple postprocessingmethod in which only MB was added in the fabrication of the gelatin film. In this case, the limited solubility of MB in the presence of the dichromate ion ~in DCG! is avoided. Nevertheless, the exposed platemust first be bathed in a dichromate solution and then developed inwater and isopropanol so that a permanent phase grating with a high DE can be obtained. To determine whether the conditions of bathing the plate in a dichromate solution are absolutely necessary, we investigated the effects of different ammonium dichromate concentrations in the film bathing solutions on the DE of the transmission hologram in this Note. The MBG films are fabricated with a method like the one suggested by Solano et al.5 The obtained gelatin film, of a 20 mm thickness, is soaked in a solution of F-5a fixer ~themethod of fabrication of our fixer is listed in Table 1! for 5 min so as to preharden it. Then the films are soaked in sensitizing solutions with different concentrations of MB dye. Some transmission gratings are recorded on the films by the use of different exposure intensities. The steps of the developmentmethod are listed in Table 2. The spatial frequency is;1070 linesymm, themax-