Lasing in cholesteric liquid crystals doped with oligothiophene derivatives

Lasing behavior has been studied in cholesteric liquid crystals (CLCs) doped with three oligothiophene (OT) derivatives such as alpha, alpha'-dimethylquaterthiophene (DMQtT) as laser dyes. CLCs spontaneously form a distributed feedback cavity, in which OT molecules are highly oriented parallel to the local director of CLCs with an order parameter of about 0.65, as studied by polarized emission spectra. Lasing occurs at only the low-energy edge of the photonic bandgap above a threshold input power of about 4.6 mJ/cm(2)/pulse in a DMQtT-doped CLC cell by pulsed (4 ns duration and 10 Hz repetition) excitation. This lasing emission mode selection is attributed to the high order parameter of OT molecules.