Highly anisotropic films of needle‐like crystallinepara‐sexiphenyl (PSP)—a promising candidate for the electroactive layer in organic light‐emitting diodes (LEDs)—can be produced using hot‐wall epitaxy, as demonstrated here (see Figure). Optical dichroic ratios of ≈11 in absorption and up to 14 in emission are measured, which is of great significance for the development of polarized LEDs.

An opto-chemical in-fibre Bragg grating (FBG) sensor for refractive index measurement in liquids has been developed using fibre side-polishing technology. At a polished site where the fibre cladding has partly been removed, a FBG is exposed to a liquid analyte via evanescent field interaction of the guided fibre mode. The Bragg wavelength of the FBG is obtained in terms of its dependence on the refractive index of the analyte. Modal and wavelength dependences have been investigated both theoretically and experimentally in order to optimize the structure of the sensor. Using working wavelengths far above the cut-off wavelength results in an enhancement of the sensitivity of the sensor. Measurements with different mode configurations lead to the separation of cross sensitivities. Besides this, a second FBG located in the unpolished part can be used to compensate for temperature effects. Application examples for monitoring fuels of varying quality as well as salt concentrations under deep borehole conditions are presented.

We report on the observation of amplified spontaneous emission and random lasing in self-organized crystalline para-sexiphenyl nanofibers. Using subpicosecond excitation, a lasing threshold is observed on the 0-1 emission band near 425 nm at excitation fluences as low as 0.5 J/cm 2 (6 ϫ10 16 cm Ϫ3 equivalent density͒, near the onset of density-dependent recombination processes. The dependence of the nonlinear emission spectrum on both the pump intensity and position of the excitation area are attributed to the interplay between random lasing and amplified spontaneous emission occurring along the nanofibers.

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