The opto-thermal effect on the encapsulated cholesteric liquid crystal

Abstract

In this paper, the transmittance of the micro-encapsulated cholesteric liquid crystal was changed by the pump beam. The opto-thermal effect, induced by the PEDOT absorbing layer, results in the variation of the transmittance on the cholesteric liquid crystal thin films. We discussed the possibility of utilizing this material for the application of flexible electronic papers by evaluating the thickness of cholesteric liquid crystal layer and the PEDOT layer, respectively. The results showed that the patterning effect is better for the sample of 12 μm thick cholesteric liquid crystal layer than that of 25 μm at the same excitation conditions and the same thickness of the PEDOT layer. And the patterning effect is better for the sample of 7.5 μm thick PEDOT than that of 5.5 μm at the same excitation conditions and the same thickness of the cholesteric liquid crystal layer. We also successfully achieved a gray-scale pattern on cholesteric liquid crystal using shutter to control the light excitation time. To explore the reason why the cholesteric liquid crystal appeared a transmittance variation when pumped, two experiments were checked: (1) Under the optical field within the pump intensity range of this experiment, the transmittance of cholesteric liquid crystal were irrelevant to the angles between the pump and probe polarizations. (2) As for the opto-thermal effects, a simple heat-conducting model was proposed to fit with the experimental results. The theoretical and experimental results agree well with this model.