Light tuning of selective Bragg diffraction of the oblique helicoidal cholesteric

It is known that the oblique helicoidal cholesteric structure (Ch$_{OH}$), which is formed in alternating electrical field applied to the chiral nematic phase (N*) at temperatures above the chiral twist-bend nematic phase (N*$_{tb}$), can show selective Bragg reflection in the visible range of spectrum. In this work, we study the effects of AC electric field at different frequencies, as well as UV irradiation on the Bragg reflection of Ch$_{OH}$ structure of the N*$_{tb}$-forming mixture containing a light sensitive chiral azo-compound. It has been found that Ch$_{OH}$ structure shows two sequential states in the tuning of selective Bragg reflection at high and low electrical fields.