Formulas are presented that provide clear physical insight into the phenomenon of extrinsic optical scattering loss in photonic crystal waveguides due to random fabrication imperfections such as surface roughness and disorder. Using a photon Green-function-tensor formalism, we derive explicit expressions for the backscattered and total transmission losses. Detailed calculations for planar photonic crystals yield extrinsic loss values in overall agreement with experimental measurements, including the full dispersion characteristics. We also report that loss in photonic crystal waveguides scales inversely with group velocity, at least, thereby raising serious questions about future low-loss applications based on operating frequencies that approach the photonic band edge.

Detailed propagation loss spectrum measurements for line-defect waveguides in silicon photonic crystal slabs are presented, which show record low loss values ͑5 dB/cm͒ and complicated frequency dependence. We quantitatively analyze the origin of the loss spectrum shape using a photon Green function theory and obtain a very good agreement, thus providing an explanation of the complex physical mechanisms responsible for the observed propagation loss. In particular, we demonstrate the influence of out-plane, backward, intermode, and in-plane scattering processes on the observed loss spectra, induced by the structural disorder that occurs during fabrication, and highlight the importance of backward and intermode scattering in these waveguides.

Plasmonic resonances in metallic nanoparticles have been used since antiquity to colour glasses. The use of metal nanostructures for surface colourization has attracted considerable interest following recent developments in plasmonics. However, current top-down colourization methods are not ideally suited to large-scale industrial applications. Here we use a bottom-up approach where picosecond laser pulses can produce a full palette of non-iridescent colours on silver, gold, copper and aluminium. We demonstrate the process on silver coins weighing up to 5 kg and bearing large topographic variations (∼1.5 cm). We find that colours are related to a single parameter, the total accumulated fluence, making the process suitable for high-throughput industrial applications. Statistical image analyses of laser-irradiated surfaces reveal various nanoparticle size distributions. Large-scale finite-difference time-domain computations based on these nanoparticle distributions reproduce trends seen in reflectance measurements, and demonstrate the key role of plasmonic resonances in colour formation.

Our molecular dynamics analysis of Xe_{147-5083} clusters identifies two mechanisms that contribute to the yet unexplained observation of extremely highly charged ions in intense laser cluster experiments. First, electron impact ionization is enhanced by the local cluster electric field, increasing the highest charge states by up to 40%; a corresponding theoretical method is developed. Second, electron-ion recombination after the laser pulse is frustrated by acceleration electric fields typically used in ion detectors. This increases the highest charge states by up to 90%, as compared to the usual assumption of total recombination of all cluster-bound electrons. Both effects together augment the highest charge states by up to 120%, in reasonable agreement with experiments.

The interaction of noble gas clusters with intense, VUV radiation is investigated by molecular dynamics simulations. It is shown that the free-electron laser cluster interaction creates a strongly coupled plasma. A new heating mechanism is identified that is more efficient than inverse Bremsstrahlung heating and explains the observation of unusually high charge states in recent experiments at DESY. The heating mechanism is a consequence of the strongly coupled plasma dynamics, in which collisional processes are strongly modified. Energy absorption takes place in the following cycle: many-body collisions, resulting in an enhanced recombination of free electrons to exited states, and subsequent reionization.