Two-photon-induced Polarization Storage And Multidimensional Storage Of Bisazobenzene Polymer

The dissertation includes two parts. Part I are the synthesis of a copolymer containing bisazobenzene chromophores poly[(methyl meth acrylate)-co-4-{(2-methacryloyloxyethyl)oxy}-4'-(4-nitrophenylazo)azobenzene)] (poly(MMA-co-M2BAN)) and the investigation on its two-photon-induced polarization storage property. Part II are the preparation of a multilayered composite film with poly[(2-hydroxyethyl meth acrylate)-co-4-{(2-methacryloyloxyethyl)oxy}-4'-(4-nitrophenylazo)azobenzene)] (poly(HEMA-co-M2BAN)) as recording layer and polyvinyl alcohol (PVA) as spacing layer, and its use for multidimensional optical storage. The main contents and results of three parts are as follows:1. A copolymer containing bisazobenzene chromophores poly(MMA-co-M2BAN) was synthesized and used for two-photon-induced polarization storage as a film. Based on two-photon-induced birefringence resulted from reorientation caused by photoselective isomerization of bisazochromophores, the data were recorded by linearly polarized Ti:Sapphire laser (wavelength: 800 nm, pulse duration: 80 fs, and repetition rate: 80 MHz). The recorded data were read by reflection confocal microscope, transmission microscope, and polarization optical microscope (POM), respectively.As the data were read by reflection confocal microscope, it was found that the recorded bits were dark dots when the polarization of the reading beam was the same as the recording beam, the recorded bits faded completely when the polarization of the reading beam was deviated with an angle of 45°, and the recorded bits became bright dots when the polarization of the reading beam was perpendicular to the recording beam. This polarization characteristic is attributed to photoinduced birefringence and optical anisotropy of the copolymer containing bisazobenzene chromophores by 2PA. Based on this polarization characteristic, polarization-binary storage was performed. That is to say two kinds of data were recorded in the same region of a given layer by separating the two polarization directions of recording beams at an angle of 45°. The relationships between the readout intensity of the recorded bit data and the recording power under two different readout modes were investigated. The results showed that there are two opposite change trends for parallel readout and perpendicular readout, respectively, and the readout threshold value is around 12 mW. Furthermore, the recorded data could be erased by erasing beam with a polarization direction perpendicular to the recording beam, and the data could be rewritten in the same region after erasing.As the data were read by transmission microscope, it was found that the recorded data were bright for parallel readout, the recorded data faded completely for 45°angular readout, and the recorded data were dark for perpendicular readout, which is consistent with the results read by reflection confocal microscope. Based on this, three-level storage was realized. In other words, when the bit data were recorded in different region of a given layer by 0°and 90°polarized beam and then read by 0°or 90°polarized beam, the readout bit data showed both bright dots and dark dots. In addition, the recorded data could be erased by circularly polarized light.As the data were read by POM, it was found that the recorded bits transformed between bright dots and dark dots by rotating the object stage in the bright light field, which coincide with the results read by transmission microscope. However, the recorded bit data presented alternate transformation between brightness and darkness by rotating the object stage in the dark light field.2. A multilayered composite film with poly(HEMA-co-M2BAN) as recording layer and PVA as spacing layer was prepared through alternately stacking. The data were recorded in the multilayered composite film by linearly polarized Ti:Sapphire laser and read by transmission microscope and POM, respectively. Polarization-multipexed and multilayered four-dimensional optical storage were successfully realized, and a storage density of 19.4 Gbits/cm3 was achieved.Comparing both readout results by transmission microscope and POM, it was found that the readout effect by POM was better than that by transmission microscope. Therefore, reading by polarizing microscope is a better readout mode.