Liquid crystal device

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A tuneable laser device comprises first and second cell walls enclosing a layer of a liquid crystal material having a helical axis substantially normal to the inner surfaces of the cell walls in the absence of an applied field. The liquid crystal contains a fluorescent, phosphorescent, luminescent or rare-earth dye. The device includes electrodes for applying a transverse electric field substantially normal to the helical axis. The invention also provides a method of electrically adjusting the peak wavelength of a photonic band edge laser comprising a chiral nematic liquid crystal material having a helical axis and a fluorescent, phosphorescent, luminescent or rare-earth dye therein and optically pumped by a suitable light source. The method comprises applying an electric field substantially perpendicular to the helical axis so as to deform the helix by means of the flexoelectric effect.