Photoinduced Refractive Index Change Of Bacteriorhodopsin And Application In Holographic Storage

Bacteriorhodopsin (BR) is a kind of unique photosensitive biological material. With the investigation of the molecular structure and properties, BR now can be modified and optimized by modern genetic engineering and biochemical methods to improve its physical and chemical properties, which show a considerable value of application. Optical storage is an important research field of BR. Based on its photochromic property; BR can be used as rewritable recording material. Here, the genetically mutated BR-D96N film is studied as recording material in holographic storage by using the conversion between B-state and M-state. The photochromic reaction of BR results in the photoinduced refractive index change. It is necessary to study the photoinduced absorption change and the photoinduced refractive index change under different wavelengths for holographic application. In this thesis, the photoinduced absorption change and the photoinduced refractive index change of the BR-D96N film are studied. The angularly multiplexed volume holographic recording is realized on the BR-D96N film. Besides, the nonlinear refractive index of the wild-type BR film is also measured by z-scan method. The main research contents includes:(1) Theoretical study of the photoinduced refractive index change of the BR-D96N film. The theoretical relationship between the photoinduced refractive index change and the photoinduced absorption change was deduced from the Kramers-Kronig relationship. By measuring the absorption change spectrum of the BR-D96N film, the spectrum of the photoinduced refractive index change was calculated.(2) Experimental measurement of the photoinduced refractive index change of the BR-D96N film. The refractive index changes were directly measured by the method of Michelson interference at several laser wavelengths (405nm, 488nm, 514nm, 633nm, 650nm). The experimental values were compared with thetheoretical values. They arc roughly consistent.(3) Experimental measurement of the nonlinear refractive index of the wild-type BR film. The nonlinear refractive index (n2) of the wild-type BR at 650nm was measured with the z-scan method. The self-defocusing effect of the BR film in red-light region was observed in the experiment.(4) Study on angularly multiplexed volume holographic recording. The holographic diffraction efficiency spectrum was theoretically calculated from the photoinduced refractive index change spectrum. Because at 633nm wavelength the diffraction efficiency is high and the erasure effect is low, the He-Ne laser (633nm) was used as the recording and readout light. The anglarly multiplexed holographic storage experiment was carried out using BR-D96N film as recording material. Six holograms were recored and reconastructed.