Proceedings PaperLaser-induced M-state holographic gratings of a hydrated D96N bacteriorhodopsin film
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A novel three-laser-beam technique that can be used to investigate holographic diffraction characteristics of an M- type and a transient dynamic hologram of a hydrated D96N mutant bacteriorhodopsin (BR) film is described in this paper. The method in both experiments is to build up molar concentrations in the M-state before holographic gratings are written. Note that the commonality between these two holograms is the M-state holographic gratings. Hence, a B-state absorption light source, a 532-nm doubled Nd:YAD laser, pumps BR molecules from the B-state to the excited M-state, then the M-state absorption beam, a 413-nm wavelength from a Krypton Ion laser, is used to write holographic gratings in that state. Writing with an M-state absorption laser induces a direct phototransition from the excited M-state to the B-state (ground state). This concept capitalizes on the bilevel BR system, i.e., depleting the ground state with a B-state absorption laser creates molar concentrations in the excited M-state, and vice versa. The reading is done with a 680-nm laser, which is far away from the absorption bands to ensure a negligible erasing effect on the gratings written in the film, resulting a pure phase hologram with high efficiency. The experimental results have shown that response times are in the order of milliseconds, and Bragg diffraction efficiency is close to 7% for this sample. Note that this CW holographic technique is a nondegenerate four-wave mixing.