Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

ABSTRACT

The field-induced orientational transition in layers of cholesteric liquid crystals with spatially periodic modulation of the surface anchoring is studied by numerical simulations and experimentally. The modulation of the surface anchoring is implemented using high-resolution focused ion-beam treatment of a polymer film providing planar alignment conditions. A specific feature of the orientational transition is that the thermodynamically stable initial planar structure with the helix axis along the normal to the layer transforms under an electric field into an equilibrium structure with a deformed lying helix (DLH) in the plane of the layer. For such a transition to occur the natural pitch of the cholesteric helix must be substantially less than the anchoring modulation period. The appearance of the DLH with a pitch corresponding to the anchoring modulation period results in strongly enhanced first-order diffraction efficiency. The orientational DLH transition is characterised by a rather narrow driving voltage range with a pronounced hysteresis. The waveguide lasing effect with characteristic of the deformed helix spectral modes is demonstrated in a range of the DLH transition.

GRAPHICAL ABSTRACT

KEYWORDS:

• Cholesteric liquid crystals
• diffraction
• electric-field-induced instability
• numerical simulation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work has been supported by Russian Foundation for Basic Research [16-29-11754 ofi_m] and (in part of development and study of the CLC photonic materials) by the Ministry of Science and Higher Education within the State assignment FSRC «Crystallography and Photonics» RAS.