Methylene blue sensitized dichromated gelatin holograms: a new electron donor for their improved photosensitivity

Tetramethylguanidine (TMG) used as the electron donor in conjunction with methylene blue sensitized dichromated gelatin (MBDCG) can produce bright reflection holograms recorded at 633 nm at an exposure level of 50 mJ/cm(2). Thus DCG hologram recording and some independence from suppliers of proprietary holographic recording materials is now open to all those with low power He-Ne lasers. The high alkalinity of the system allows the unexposed coated material to have an effective lifetime at room temperature of weeks rather than days. Its low dichromate content has an environmental advantage over the usual DCG formulations. Replacement of methylene blue by eosin can produce similar photosensitivity to 514 nm. The superiority of TMG over previously reported electron donors used with MBDCG is discussed.