Research On Key Technologies Of Femtosecond Laser Multi-dimensional Data Storage

The urgently increasing requirement on data storage capacity makes the super-high density storage technology to be one of the most important research topics. Different from the traditional optical storage technologies which depends on shortening the laser wavelength and decreasing the objective numerical aperture to achieve higher storage density, multi-dimensional data storage introduces other parameters besides the geometric space that can influence the recording and reading process, builds individual coordinates, finally records multiplex information inside the identical space of storage medium. Recorded data can be individually read out. This technology has the advantage of super-high storage capacity and easy to control. It has become a promising candidate for next generation optical storage. In this dissertation, both the high resolution of two-photon absorption and photoinduced isomeric reorientation properties of azobenzene chromophores are combined to develop a novel polarization-multiplexed and multilevel data storage method. Some key issues of the multi-dimensional data storage are theoretically and experimentally investigated.Firstly, the two-photon optical response property and mechanism of azobenzene polymer is introduced, including photoinduced isomerization, reorientation and orientational hole burning; The two-photon isomerization rate equation and reorientation rate equation are described; Furthermore, as the most important anisotropy character, photoinduced birefringence is theoretically analyzed and experimentally measured; Z scan technique, which is wildly used to characterize the material nonlinear optical properties, is introduced and the experimental result is analyzed.Secondly, a femtosecond laser two-photon polarization storage system is built to achieve polarization multiplexed data storage; Transmission polarized light readout configuration, polarizing microscopy, and reflective scanning confocal microscopy setup are respectively used to read out the recorded bits, and the feasibility of erasable and rewritable polarization storage is confirmed; The storage density can reach as high as250Gb/cm3; The influence of exposure dose (e.g. exposure time, power) on the bits intensity and size is also investigated, providing a basis for the optimization of recording parameters. Thirdly, when the exposure dose exceeds one threshold during the polarization recording in poly(M2BAN-co-MMA), dark dots will appear when perpendicular readout. This phenomenon is used to perform polarization multilevel storage; At the same time, nine-level storage is realized by modulating the exposure dose; Some influencing factors are discussed for multilevel storage; The surface deformation induced by polarized femtosecond laser is deeply studied; The optical-field gradient force model is applied to explain the surface deformation; Three-stage recording in polarization storage is discussed.Finally, basic research on three-dimensional parallel recording based on spatial light modulator (SLM) is carried out; The structure and modulation mechanism of SLM are circumstantiated;3D computer generate hologram (CGH) algorithm is designed and multi-layer images reconstruction is performed based on this; The defocus and spherical aberration caused by refractive mismatch are considered and proposed to be compensated in the3D computer generate hologram algorithm; All the work lay a foundation for next step parallel multi-dimensional data storage and dynamic holographic parallel processing technology.