Simon K. H. Wei

Robust organic lasers comprising glassy-cholesteric pentafluorene doped with a red-emitting oligofluorene

Doped with a red-emitting oligofluorene, fluid and glassy cholesteric liquid crystal (CLC) films are characterized by similar lasing thresholds and efficiencies. With picosecond excitations the output from a glassy CLC laser is temporally stable, but that from a fluid CLC laser decays with time. The difference in stability is attributable to external perturbations on supramolecular structure in the fluid but not the solid state, such as heating through optical pumping, light-induced pitch dilation, and laser-induced flow.

High-damage-threshold static laser beam shaping using optically patterned liquid-crystal devices

Beam shaping of coherent laser beams is demonstrated using liquid crystal (LC) cells with optically patterned pixels. The twist angle of a nematic LC is locally set to either 0 or 90° by an alignment layer prepared via exposure to polarized UV light. The two distinct pixel types induce either no polarization rotation or a 90° polarization rotation, respectively, on a linearly polarized optical field. An LC device placed between polarizers functions as a binary transmission beam shaper with a highly improved damage threshold compared to metal beam shapers. Using a coumarin-based photoalignment layer, various devices have been fabricated and tested, with a measured single-shot nanosecond damage threshold higher than 30 J/cm2.

Spatially resolved lasers using a glassy cholesteric liquid crystal film with lateral pitch gradient

To fabricate spatially resolved glassy cholesteric liquid crystal (CLC) lasers, a lateral pitch gradient was introduced by thermally activated diffusion across the interface of two films comprising nematic and cholesteric oligofluorene doped with a red-emitting oligifluorene. The formation of spatially resolved Grandjean–Cano bands was accountable by strong surface anchoring at substrates and the qualitative chiral concentration profile. Across each band there was a common stop band, and a set of bands produced multiple lasing peaks across the spectral range determined by light-emitter’s fluorescence spectrum. The resultant lasing thresholds, 6.6–7.6 mJ/cm2, and slope efficiencies, 0.2%–1.5%, are superior to those reported to date for gradient-pitch CLC lasers.

Novel Organic Light-Emitting Materials Capable of Variable Charge Injection and Transport

Novel organic materials were designed and synthesized by attaching monodisperse oligofluorenes to a hole- and an electron-conducting core through a flexible spacer. These material class holds promise for the realization of efficient and stable OLEDs. Article not available.