Determination of liquid crystal orientation in holographic polymer dispersed liquid crystals by linear and nonlinear optics

The liquid crystal alignment imposed during the fabrication process of one-dimensional transmission gratings, holographically formed in a polymer dispersed liquid crystal, is determined by linear optical birefringence as well as rotational second harmonic generation. For a mixture consisting of nematic liquid crystal E7, a pentafunctional acrylate monomer, and a photoinitiator, the director orientation inside the liquid-crystal-rich layer is found to be approximately along the grating direction. We suggest that this molecular orientation is the consequence of the strong flow during the grating formation.