  Heliconical cholesteric liquid crystals are expected to be more sensitive to
torque induced by light field since their structure allows both bend and twist
in molecular orientations, differently from the conventional cholesterics in
which only twist deformation is involved, requiring much higher fields. We
report here a demonstration of tuning the helical pitch in heliconical
cholesterics induced by an optical torque. Experimental observations are in
agreement with expectations of the classical theory extended to include the
effect of the optical field. A dual control of the helical pitch is achieved
including both the low-frequency electric field applied along the helix axis
and the optical field orthogonal to it.
