| dc.description.abstract | In this thesis, we mainly investigate the spectral characteristics and their root causes of cholesteric liquid crystals (CLCs) with Helfrich deformation. The research topic includes the following two parts. In the first part, we analyze the influences of different physical parameters on the CLCs with Helfrich deformation. According to the measured transmissive spectra of the CLCs applied with electric fields and the observed images under a polarized optical microscopy, the threshold voltage of the Helfrich deformation in each condition can be confirmed. In addition, we also elucidate the differences between them and the corresponding reasons according to the changes of the reflection bands. Furthermore, by varying the cell gap, alignment film, and concentration of the adopted materials, it is found that the CLCs doped with liquid crystal dimer have a lower threshold voltage of the Helfrich deformation, and the transmission spectrum of each condition possesses the feature of broadening the reflection band width. Besides, the homogenous alignment layer can enhance this effect. In the second part, we analyze the spectral characteristics of CLCs with Helfrich deformation, which differ from those of the previous CLCs. The obtained wavelength bands of the transmission spectra and the reflection spectra are different. The cause of this phenomenon can be verified by the Berreman 4 × 4 matrix simulation, and be concluded to be similar to waveguide effect due to such structures. The CLC structures are divided into three layers for simple discussion, namely the middle layer with the Helfrich deformation structure and the boundary layers closed to the substrates with general planar textures of CLCs. The transmission and reflection between the layers of the structures can be clarified from the simulated spectra. Due to the structural characteristics of the Helfrich deformation, the reflected light is reflected back and forth between the boundary layers and the middle layer, so the wavelength bands of the measured reflection and transmission spectra of CLCs with Helfrich deformation are different. | en_US |