  Polarization dependence of opto-mechanical behavior of monodomain
photochromic glassy liquid crystal (LC) polymers under polarized ultraviolet
light (PUV) is studied. Trans-cis photo-isomerization is generally known to be
most intense at 'parallel illumination' (polarization parallel to LC director),
as light-medium interactions are active when polarization aligns with
trainsition dipole moment. We show that at parallel illumination though cis
isomers are converted from trans the most near surface, they can be the least
below certain light propagation depth. Membrane force, an average effect of
trans-cis conversion over propagation depths, shows a monotonic polarization
dependence, i.e. maximum at parallel illumination, which agrees well with
experiment [1]. However, under strong illumination, cis
fraction/photo-contraction distribution through depths shows deep penetration,
switching over the polarization dependence in photo-moment, which is related to
photo-contraction gradient ---- photo-moment can be maximum at 'perpendicular
illumination' (polarization perpendicular to director) under strong light. We
give both intuitive explanation and analytical demonstration in thin strip
limit for the switchover.
