Uli Lemmer

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Photograph of a mechanically flexible 2D-DFB laser made from the conjugated polymer MeLPPP. The laser is optically pumped well above the threshold for amplified spontaneous emission. The complex far-field emission pattern (blue-green) results from a large detuning between the resonance wavelength and the gain maximum. • A nearly diffraction limited surface(More)
The photo-Dember effect is a source of impulsive THz emission following femtosecond pulsed optical excitation. This emission results from the ultrafast spatial separation of electron-hole pairs in strong carrier gradients due to their different diffusion coefficients. The associated time dependent polarization is oriented perpendicular to the excited(More)
The use of organic optoelectronic devices such as organic light-emitting diodes and organic photodiodes in micro-optical systems is discussed. Potential applications like optical interconnects and optical sensor systems are examined. Device characteristics including emission spectra, I-V-curves and the dynamic behaviour are analysed. In the combination with(More)
Except where specific reference is made to the work of others, this work is original and has not been already submitted either wholly or in part to satisfy any degree requirement at this or any other university. The picture on the front page shows a true color image of a sample containing gold and silver nanospheres as well as gold nanorods photographed(More)
We demonstrate red-emitting silicon quantum dot (SiQD) phosphors as a low-cost and environment-friendly alternative to rare-earth element phosphors or CdSe quantum dots. After surface passivation, the SiQD-phosphors achieve high photoluminescence quantum yield = 51% with 365-nm excitation. The phosphors also have a peak photoluminescence wavelength at 630(More)
We have realized a 76 MHz white-light differential transmission spectroscopy system. The technique employs a Ti:sapphire laser oscillator and a tapered fiber to generate a white-light continuum spanning almost the full visible to near-infrared spectral range. Using acousto-optical modulation and subsequent lock-in detection, transient relative transmission(More)
Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy, Dielectrophoretic assembly of high-density arrays of individual graphene devices for rapid screening, Defect imaging in single-walled carbon nanotubes by voltage-contrast scanning Controlled fabrication of single-walled carbon nanotube electrodes by(More)
We have investigated the broadband terahertz (THz) optical properties of nanoporous silicon samples with different porosities and the ultrafast carrier dynamics of photogenerated charge carriers in these materials. Following photoexcitation, we observe a fast carrier recovery time consisting of two dominant recombination processes with decay constants below(More)
Lasing mechanisms in organic photonic crystal lasers with two-dimensional distributed feedback, Lasing action in two-dimensional photonic crystal lasers with hexagonal symmetry, Shrinkage precompensation of holographic three-dimensional photonic-crystal templates, Transition between corrugated metal films and split-ring-resonator arrays, Appl. Fabrication(More)