  Liquid crystal layers sandwiched between a reference plate and a
photosensitive substrate were investigated. We focused on the reverse geometry,
where the cell was illuminated by a laser beam from the reference side. In
planar cells instabilities occurred, static and dynamic ones, depending on the
angle between the laser polarization and the director orientation on the
reference plate. In cells where the molecules were aligned along the normal of
the reference plate, dynamic pattern was observed at all angles of
polarization. A simple model based on a photo-induced surface torque gives
account of the findings. Light scattering studies revealed some basic
properties of the instabilities.
