Holographic Storage Based On Plasmon Spectra Regulation In Ag/TiO₂ Composite Films

Nowadays,the society is stepping into information age.It is urgent to develop storage technology with high density,low energy consumption and long life.Holographic storage,using photon as a carrier,records amplitude and phase information,which can reproduce the real three-dimensional and full-color image of the object.Holographic multiplexing technology can realize multi-dimensional storage to meet the requirement of high-density information storage.Optical storage media is an important component of holographic memory device.The design and preparation of high-sensitive optical media are the keys to realize the multiplexing holographic storage.Ag/Ti O₂ composite in nanoscale exhibits multicolor photochromism.The great challenge in this field is how to realize high-density optical storage and color holographic reconstruction on a single medium.It relies on regulating the morphology and size of Ag nanoparticles effectively,enhancing the sensitivity of the composite system at the wavelength and polarization of light,and improving the holographic multiplexing efficiency.In order to resolve the problem,the thesis adopts the methods of visible laser assisted electron donor and dual frequency laser co-reduction.The localized surface plasmon resonance absorption spectra of Ag nanoparticles deposited in Ti O₂ porous films were regulated.Holographic storage and readout were carried out accordingly.The research work is divided into three parts:1.Narrow-band plasmon spectra regulation and its application.The small molecules of tannic acid were introduced into the Ag/Ti O₂ nanocomposite films by immersion method.The electron release efficiency was improved by electron donor effect stimulated by visible light irradiation.The Ag nanoparticles with high concentration and uniform size were obtained by tannic acid reduction in Ti O₂ porous films by laser excitation in visible light band.Resultantly,narrow-band plasmon resonance absorption spectra were formed.In addition,the samples were characterized for the methods of blue-violet laser reduction and tannic acid thermal reduction.Using Lorentz model,the absorption spectra of Ag/Ti O₂ nanocomposite films prepared by different methods were fitted,and the spectral characteristic parameters were obtained.At the same time,combining with the morphology characteristics of Ag nanoparticles for different samples,the important parameters to characterize the spectral narrowing were obtained.By analyzing the dynamic curves of blue light（473 nm）in s-s polarization configuration of samples prepared by different methods,it is concluded that spectral narrowing is the key to improve the holographic storage efficiency and rate at a certain wavelength.Furthermore,in the Ag/Ti O₂ film with narrow-band absorption spectrum,the holographic multiplexing storage in orthogonal circularly polarized configuration was realized.Based on the high correlation between the circularly polarized state and the reconstructed position in the holographic diffraction process,the real colorful reconstruction of the multiplexed hologram was realized by using polarization as the chrominance division channel.2.Surface ion modification and plasmon spectra optimization.On the basis of the first part of the work,the Ag/Ti O₂ nanocomposite films were modified with potassium chloride solution to optimize absorption band of Ag localized surface plasmon resonance.Compared with the photochromic properties of Ag/Ti O₂ obtained in the first part,it was found that the photochromic rate of Ag/Ti O₂ modified by KCl was accelerated due to the presence of chloride ions.The effects of different concentrations of KCl and immersion times of KCl solution on the photochromism of the films were studied.The fitting to spectral hole burning rate was carried out,and the fitting results were analyzed accordingly.Under the irradiation of blue laser（473 nm）,the holographic dynamic curves for different writing light powers in s-s configuration were compared.The response rate and diffraction efficiency of holographic storage were compared and analyzed.At the same time,peristrophic multiplexing dynamic curve and multiple hologram storage were obtained in the Ag/Ti O₂ film modified with KCl for s-s polarization configuration（473 nm）,and the hologram reconstruction was realized.3.Bicolor laser collaborative reduction for polarization sensitive spectral hole burning.Under the co-irradiation of UV and visible laser,anisotropic Ag nanoparticles were reduced from Ti O₂ nanoporous film adsorbed by polyacid molecules.The UV light plays a dominant role in the reduction,and the visible light acts as auxiliary photo-dissolution.Under the influence of the electron acceptor effect of silicotungstic acid,the photo-dissolution is accelerated.Due to the polarization of laser beams,the directional dissolution is formed,thus resulting in the growth of anisotropic nanoparticles.The photochromic properties of the films irradiated by the laser beams of different wavelength（473 nm and 671 nm）were studied.It is concluded that the film has high polarization sensitivity and high holographic diffraction efficiency in orthogonally linear polarization mode.Red light was used as writing light,and different polarization configurations（s-p and s-s）were taken into account.Holographic recordings in single-mode and polarization multiplexing mode were carried out.The optimized multiplexing recording mode and recording time were obtained.Linearly polarized state was used as chrominance division channel to realize holographic reconstruction with adjustable colors.