Johannes Boneberg

Temperature dependence of optical properties for amorphous silicon at wavelengths of 632.8 and 752 nm

The temperature dependence of the optical properties for amorphous silicon is studied at wavelengths of 632.8 and 752 nm. Both the refractive index and extinction coefficient increase linearly with temperature for 752 nm, while the refractive index decreases and the extinction coefficient increases for 632.8 nm. The rate of increase of the extinction coefficient at 632.8 nm is twice as much as that for 752 nm.

Characterization and applications of plasmon fields in metal nanostructures

The excitation of plasmons in metallic nanostructures by light can give rise to pronounced local optical field enhancement with respect to the incident electromagnetic field. The details of these optical near fields depend sensitively on the properties of the nanostructures (material, size and shape), on the light wavelength and polarization, and also on the substrate. In this article we discuss several of these aspects influencing the near-field distribution for a given object and the resulting surface ablation by optical near fields. To this end we use both experimental and simulation techniques. Additionally we will present first results of experiments investigating the light emitted during nanoscale ablation. Finally, we will present an example how plasmon-mediated near-field effects act on the conductance of atomic-size contacts.

Laser cleaning of oxidized metallic materials: role of the optical properties of the oxide films

In the present work, the effects of nanosecond pulsed laser irradiation on oxidized metallic surfaces were investigated, in order to estimate the possibility of using laser techniques for cleaning applications. After oxidation, the oxide layer developed on the metallic surfaces depends on the composition of the substrate and also on oxidation conditions. In this study a modeling system: pure Fe oxidized at 500 degrees C, has been investigated. The influence of the optical properties of the oxide films on the removal mechanisms and the cleaning efficiency of the laser technique was illustrated by performing specific electrochemical treatments.

Dynamics of the optical parameters of molten silicon during nanosecond laser annealing

The behavior of the reflectivity of a Si single crystal during irradiation with two successive Nd:YAG pulses is investigated with ns resolution. The first pulse melts the surface, and therefore the reflection coefficient increases to the value of the metallic liquid at the melting temperature. Upon further heating of the surface with the second pulse, we observe a decrease of the reflection coefficient, resulting from the temperature dependent dielectric function of the molten Si. The largest decrease in the reflectivity that could be reached before damaging the surface amounted to 9% for both wavelengths 633 nm and 488 nm.