Molecularly oriented surface relief formation and multi-directionally oriented crossed gratings in photoreactive liquid crystalline copolymer films

Abstract

This paper demonstrates formation of surface relief (SR) gratings and crossed SR gratings with molecularly oriented structure using photo-cross-linkable liquid crystalline copolymer films by means of holographic exposure of 325 nm He- Cd laser beams combined with linearly polarized (LP) UV light. For the intensity holography using He-Cd laser, SR gratings were formed after annealing the exposed films, where the molecular migration from the lower to the higherexposed region occurred. The reorientational part and SR height were dependent on degree of the photoreaction. When the exposure doses were low, molecular reorientation at the convex region was generated. In contrast, higher exposing doses resulted in the molecular reorientation at the concave area. The resulting gratings showed polarization sensitivity for diffraction efficiencies of the probe light beam according to the molecularly reorientation direction. Furthermore, multi-holographic exposure yielded crossed SR gratings with reoriented structure according the polarization direction of He-Cd laser beams, which exhibited multi-functional diffractions. Furthermore, when combining the multi-holographic exposure and the unidirectional LPUV light exposure, crossed SR grating with multi-directionally oriented film structure was generated., where the whole area was reoriented.