Phase-Type Gratings Formed by Photochemical Phase Transition of Polymer Azobenzene Liquid Crystal. 2. Rapid Switching of Diffraction Beams in Thin Films

Abstract

Dynamic holographic gratings were investigated with thin films of polymer azobenzene liquid crystals by periodic induction of photochemical nematic-to-isotropic phase transition. On irradiation of writing beams (488 nm), multiple diffraction beams of a reading beam (633 nm) were immediately observed. The firstorder diffraction efficiency reached to a maximum value within several tens of milliseconds: the rise time was approximately 50 ms for PM6AB2 films and 30 ms for PA6ABCN films. Quite large modulation in refractive index (∼0.08) was obtained in both polymer films. Studies on effects of temperature and light intensity on the grating formation suggested that photochemical reactions of azobenzene moieties followed by photochemical phase transition in bright fringes of the interference pattern would be responsible for the formation of holographic gratings. By turning on and off the writing beams, the diffraction beams could be switched dynamically without significant fatigue.

Photocontrolled Reversible Dimensional Changes of Microstructured Photochromic Polymers

“…Specifically, most of the gratings with similar thickness as the here presented, are produced after irradiation with interfering beams that cause variation of the refractive index inside the samples mainly consisting of azobenzene polymers and liquid crystals. In these studies the switching procedure in the DE is due to the formation and deletion of the gratings (Yamamoto et al 2001. Moreover, although the thickness of the produced gratings is very small, they exhibit higher DE than most of the volume gratings prepared in this regime (Tong et al 2005, Yamamoto et al 2001.…”

“…In these studies the switching procedure in the DE is due to the formation and deletion of the gratings (Yamamoto et al 2001. Moreover, although the thickness of the produced gratings is very small, they exhibit higher DE than most of the volume gratings prepared in this regime (Tong et al 2005, Yamamoto et al 2001.…”

“…The gradual wettability changes are exclusively based on the photochemical modification of the embedded photochromic molecules caused by the photoisomerization process. In addition, in the case of the diffraction gratings the development was generally done by interference of different polarized laser beams, or by electric-field application, and the modification of their diffraction efficiency is connected with the changes of the refractive index of the photochromic molecules during this procedure (Yamamoto et al 2001. Here we present how the volume changes induced to the photochromic polymers by the photoisomerization of their embedded photochromic molecules, can improve significantly the performance of these two different type of applications, namely the microfluidic devices and the diffraction gratings.…”

Azobenzene Polymers for Photonic Applications

“…In the case of liquid crystal samples, light induces a spatial pattern of nematic and isotropic zones (which have different refractive indices). These holographic phase grating can be rapidly formed, erased, and switched (Yamamoto et al, 2001). …”

New Azobenzene Chromophores as Monomers for Synthesis of Polyesters

“…It is expected that holography is the most promising technique for establishing photonics as a future technology. 3 The possibility of using such types of photochromic polymers for reversible optical storage, holographic or digital was first suggested in 1984. The real interest in the subject started in 1987, when Wendorff demonstrated reversible optical storage properties us-ing liquid-crystalline (LC) polymers.…”