Focused Polarization Gratings in an Azobenzene-Based Molecular Glassy Film

Holograms recorded by focused light beams have several advantages over usual plane wave holograms such as reduced size, white light readout possibility and others. Focused polarization grating recording in an azobenzene-based molecular glasy film 5,5,5-triphenylpentyl 4-((4-(2-(4-bis(2-hydroxyethyl)amino)phenyl)-1-cyanovinyl)phenyl)dyazenyl)benzoate (which we shortly denoted as B11) is experimentally studied and compared with such grating recording in other materials. It has been determined that focusing manifests itself differently than in other materials, e.g., as in a-As₂S₃ and a-As-S-Se chalcogenide films. Thus, it reduces the holographic grating recording efficiency independently of recording and readout beam polarizations. It has also been found that recording efficiency with circularly and orthogonally L-R polarized beams is higher than with linearly polarized p-p beams. The highest diffraction eficiency of 26% is achieved with L-R polarized unfocused beams.

Recording efficiency grating period dependences for unfocused beams at 200 J/cm² exposure and at 1000 J/cm² exposure are different with a maxima at 2 μm and 6 μm, respectively. In contrast, recording efficiency grating period dependences for focused beams at 200 J/cm² exposure and at 1000 J/cm² exposure are the same with the maximum at 6 μm.

The obtained results are discussed in terms of trans-cis-trans photoisomerization followed by mass transfer and their light intensity dependence, light electric field gradient force, the photoinduced light scattering and photoelastic forces.