| Three-dimensional volume holographic storage exhibits strong competitiveness in information storage technology due to its advantages of high storage density,fast data transmission rate,rapid addressing rate,long storage lifetime,and low cost.However,this technology has been limited by its response time.As a result,it has not been popularized in practical application.Therefore,the investigations into fast response volume holographic storage are of great significance and value.Based on two materials,one is the PQ/PMMA photopolymer with phenanthraquinone(PQ)as initiator,in which the ultrafast volume holographic storage under nanosecond pulsed exposure is realized The other is TI/PMMA polymer with IRGACURE 784(TI)as initiator,in which the response of millisecond magnitude in volume holographic storage is realized.Ultrafast volume holographic storage in PQ/PMMA polymer is realized under nanosecond pulsed exposure for the first time.In the experiment,a pulsed laser with 6 ns pulse-width and 532 nm wavelength is used to record the holographic grating in 2 mm thick material under a single pulse exposure.When the dark reaction time reaches 15 min,the maximum grating strength(1 %)is obtained.After that,the maximum diffraction efficiency of the holographic grating is obtained by 32.9 % under 300 cumulative multi-pulse exposures,and the corresponding grating response time is 0.88 ?s.When the cumulative exposure time is 1.5 ?s,the angle multiplexing technology is used to realize the multiplexing storage of five holograms with the dynamic range M# of 0.726.The ultrafast volume holographic storage performance is improved by doping Ag nanoparticles.The experimental results indicate that by doping Ag nanoparticles with a particle size of 80 nm and a concentration of 0.00006 wt%,the diffraction efficiency is enhanced by 18.5 %,while the response time is shortened by 67 % and the dynamic range M# is increased by 70 %.A dynamic model of multi-component mixed modulation induced by Ag nanoparticles is established,and it is proposed that the absorption modulation is generated during exposure due to localized surface plasma resonance(LSPR)of Ag nanoparticles.By doping Ag nanoparticles with a particle size of 80 nm and a concentration of 0.00006 wt%,the maximum absorption modulation of 8.2×10-5 is obtained.Compared with the refractive index modulation(9×10-5),the introduction of absorption modulation enhances the total modulation depth by 91 %.A novel initiator IRGACURE 784(TI)is introduced into polymethyl methacrylate(PMMA)substrates,and TI/PMMA polymer materials are prepared by an improved three-step polymerization method with an optimal initiator concentration of 4.0 wt%.The basic holographic properties of 3 mm thick TI/PMMA and PQ/PMMA polymers are examined under 532 nm exposure.The experimental results indicate that the diffraction efficiency of 74 %,the response time of 20.5 s,and the dynamic range M# of 6.88 are obtained in TI/PMMA polymers with an exposure density of 115 m W/cm2.Compared with PQ/PMMA materials,the diffraction efficiency of TI/PMMA materials is improved by 28 %,while the response time is shortened by 53 %,and the dynamic range M# is improved by 96 %.Under 532 nm exposure,the basic holographic properties of 1-3mm thick TI/PMMMA polymers are experimentally investigated.The 1 mm thick material exhibits faster response time(4.98 s),while the 3 mm thick material owns a higher diffraction efficiency(74 %)and a larger dynamic range M#(6.88).By introducing the thickness-dependent absorption coefficient formula,combining the non-local diffusion model and the photopolymerization rate equation,the grating dynamics model of TI/PMMA polymers in the absorption attenuation process is established,and the theoretical simulation was consistent with that of experimental results.In the experiment,the grating strength changes from weak to strong,and the response time changes from slow to fast with the increment of recording time under pulsed exposure.However,as the recording time is shortened,the response time of holographic grating increases and become much longer than that of recording time,that is,the holographic reciprocity law mismatch occurs.The dark diffusion enhancement process is needed to improve the diffraction efficiency under ultrafast holographic recording.For this reason,a probability calculation of the holographic reciprocity law mismatch is proposed.The analysis exhibits that the effect of reciprocity law mismatch on grating strength can be restrained by increasing the exposure energy density and shortening the polymerization rate.For TI/PMMA polymers,the corresponding matching range of exposure duration in 10-3?102 s is obtained.The dark reaction process of TI/PMMA polymers after a single short-time exposure in milliseconds is experimentally examined.The experimental results indicate that a shorter exposure duration is followed with a smaller original grating strength,longer dark reaction time and higher contribution of the dark reaction process to the diffraction efficiency.The dark reaction process is influenced by the short-time exposure durations,which verifies the applicability of the model.On this basis,the absorption attenuation dynamics model of TI/PMMA polymers under short-time exposure is established,and the optical physical-chemical process in TI/PMMA polymers is theoretically described,which is found to be consistent with experimental results.Based on the theory of polarization holography under the three-order dielectric tensor,polarization volume holographic storage of TI/PMMA polymers are investigated.The experimental results indicate that TI/PMMA polymer has photo-induced birefringence effect,and its maximum modulation is 9.06×10-5.Therefore,non-parallel polarized incident exposure can be used to record the polarization grating in TI/PMMA polymers.In the experiment,the incident beams with different polarization angles,30 °,45 °,60 °,and 90 ° included,is used to record the amplitude,phase,and polarization information.Multi-dimensional(angular-polarization)multiplexing storage of holographic grating is realized under the orthogonal polarization recording,and the dynamic range M# of 1.23 is obtained.It is shown this thesis that PQ/PMMA and TI/PMMA polymers have good volume holographic properties with fast response,which indicates they are two kinds of highly competitive photopolymer materials in the field of volume holographic storage. |
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