Title : Lasing polarization peculiarities in cholesterics separated by dye doped polymeric layer
Abstract:
Cholesteric liquid crystals (CLC) are the most famous representatives among the one-dimensional (1D) chiral soft photonic crystals. The investigation of liquid crystals (LC) includes a wide range: chemical structure, physical properties and technical applications. In this work, the physical properties and application areas of LCs are investigated. LCs are optically anisotropic materials which means that the speed of light waves in the medium depends on the direction and polarization of light. The property of anisotropy of liquid crystals leads to spatial modulation of refractive index i.e. the material possesses different refractive indexes in different directions. So, the control of light leads to the so-called photonic bandgap (PBG) existence in the medium where the selective reflection of light occurs. LCs are interesting materials also in regard to PBG control via external factors e.g. temperature, light, electromagnetic field, etc. All these properties make them attractive in different applications such as lasers, optical shutters, filters, displays, etc. There are two approaches to induce optical defects inside the CLC structure: either by introducing of iso-tropic/anisotropic defect layer or creating of a phase jump by external factors (induced defects). The CLCs with defect layers inside them have been recently considered in view of generating additional modes in spectra and the possibility of low threshold lasing on these modes. There are many theoretical/experimental results dedicated to the defect modes existence inside the PBG of CLC. In this work we experimentally investigated the lasing possibility from the CLC - dye-doped isotropic polymer layer- CLC threelayered wedge-shaped system and investigated the polarization state of laser modes generated from the defect modes inside the PBG. The information about polarization is important in different applications’ points of view such as information decoding in different polarization states, etc. The defect modes existence for our experimental study also verified theoretically. For our experiment, the wedge-shaped three-layered system was prepared where two CLC layers provide wedge-shape of the cell. Continuously changing the CLC layers’ thickness gives an opportunity to obtain continuous circularly polarized lasing using a linearly polarized excitation beam.
