Spatially tunable emissions of dye-doped liquid crystal lasers between the cholesteric and smectic phases

Spatially tunable lasing emissions from dye-doped heavy chiral concentration liquid crystals (DD-HCCLCs) were investigated in this work. After thermal control of HCCLCs to below the phase transition temperature, the central wavelength of the photonic bandgap (PBG) was sensitively related to the working temperature, which could be tuned widely with the relatively small temperature variation owing to the phase transition from the cholesteric (Ch) to the smectic (Sm) phase. By means of Keating’s theory, the change in helical pitch, obtained from the transmission spectrum, versus temperature can be well fitted to derive the phase transition temperature of the smectic A phase. As the pump beam was focused on different locations of the DD-HCCLC cell with a one-dimensional temperature gradient, we demonstrated spatially tunable lasing peaks over one hundred nanometers from 556 nm to 671 nm. The experimental result regarding the spatially tunable lasing property shows that the DD-HCCLC laser could be a promising light source in display technology.