Study On Polarization Holography Image Storage In Azo-containing Polymers

In the past decades, azobenzene containing polymers have attracted considerable interest in optical storage owing to their outstanding photoactive characteristics. It is well known that azo molecules can undergo trans-cis-trans isomerization cycles under the irradiation at the wavelength lying in the absorption region. If the pump light is linearly polarized, the molecules will be oriented perpendicular to the pump polarization direction. This photoinduced orientation results in macroscopic anisotropy, thus the dichroism and birefringence in polymer films. Since azo molecules can be photo-oriented, irradiating with a light field whose polarization is periodically modulated in space can induce the periodical orientation of molecules correspondingly, i.e. polarization holographic recording. The obtained polarization gratings are very useful in fabricating highly functionalized optical devices because they can control both the beam propagation direction and polarization state. This thesis gives a detailed description of the polarization holography and optical image storage in azo polymer films.First of all, the optical properties of azo polymers are introduced. Especially the characteristics of nonlinear optics, photo-isomerization and photoinduced anisotropy are emphasized, because they are crucial for optical storage.Second, on the basis of the characterization of photoinduced anisotropy, polarization holographic recordings are accomplished in the azo-containing liquid crystalline polymer. Pure polarization gratings are recorded by two 532 nm laser beams with orthogonal linear polarizations. Furthermore, the polarization holography in the azo-containing liquid crystalline polymer is extended to two-dimensional (2D) recordings, i.e. polarization gratings overlap at the same place through multiple recordings. The 2D polarization grating in present makes up of two orthogonal 1D polarization gratings, which are written by two orthogonally polarized 532 nm beams (linearly or circularly). The diffraction properties of the 2D gratings are investigated. It is found that the diffraction efficiency of 2D grating is lower than that of 1D grating, and the 2D grating acts as the integration of its componential 1D gratings.At last, we put emphasis on the Spatial Light Modulator(SLM). Based on this optical component, we record polarization holography images storage in an azo ionic liquid crystalline polymer.