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The role of the thermally modulated order parameter in the diffusive laser action observed in dye doped nematic liquid crystals was investigated. Above a given pump energy a randomly distributed series of bright tiny spots appear, giving rise to a strongly fluctuating emission pattern. The spectral analysis reveals discrete sharp peaks (about 0.5 nm) slightly blueshifted with respect to the highest efficiency region of the gain medium. A comparative study was performed in systems having different sizes and confining geometries, corroborating the idea that the random lasing observed in dye doped nematic phase is fluctuation driven through a recurrent multiple scattering process. [ABSTRACT FROM AUTHOR]

Peculiar light emission properties have been observed in cylindrical microcavity hosting dye-doped helixed liquid crystals, which behaves as a fiber-like multidirectional distributed feedback laser. Experimental studies performed for this level of confinement show that laser action is exhibited both axially and radially, indicating a self-organized three-dimensional blue phase-like configuration. Thermal wavelength tunability was observed for both orientations emphasizing two different linear behaviors. The distributed feedback mechanism and the Q factor of the mirrorless resonant cavity result enhanced for axial stimulated emission because of the significant increase in the number of helical periods. In addition, long-lived spectrally narrow defect modes appear within the photonic band gap owing to optical phase jumps which take place in local structural defects. [ABSTRACT FROM AUTHOR]

The trap-assisted electron tunneling in thin insulators has been modeled to explain the apparition of plateaus in the current-voltage characteristics of some existing experimental data. As a consequence of the electron tight confinement in the trap, the charge therein has a steplike variation with the voltage increase, a feature that further translates into wide plateaus of the current-voltage diagrams, in accordance with some experimental data. The temperature dependence of these diagrams has been included into the model and compares well with the experimental evidence. The possibility of quantitatively comparing the model computations with the measured data opens useful insight into trap’s physical properties such as spatial extent or energy depth. [ABSTRACT FROM AUTHOR]