DC-field-assisted grating formation and nonlinear diffractions in methyl-red dye-doped blue phase liquid crystals.

We report the observation of enhanced nonlinear optical responses of methyl-red-doped blue-phase liquid crystals by application of a DC field. We have observed strong multi-order nonlinear grating diffractions characterized by a nonlinear index coefficient n(2)∼0.5  cm(2)/W using unfocused CW laser power of ∼1  mW and a DC field of a few V/μm. The underlying mechanisms are crystalline lattice and director axis reorientations by torques exerted by the DC field and photo-excited dye molecules.