Institute of Technical Physics

shown that the latter systems are necessarily dispersive in contrast to the former ones. In the end we discuss a published example where the mixing of expressions of both versions of Maxwell's Equations leads to unphysical conclusions. The presentation demonstrates for students how flexible can be the work with different versions of electrodynamics but also how carefully one has to be thereby.

This paper reports the micromachining results of di erent materials (Al, Si, InP and fused silica) using a Ti : sapphire laser at the wavelength of 800 and 267 nm with variable pulse lengths in the range from 100 fs to 10 ps. The hole arrays with a diameter up to a few m through microdrilling are presented. We discussed how an e ective suppression of the thermal di usion inside the ablated materials and an e ective microablation could be realized. If the laser uence is taken only slightly above the threshold, a hole array can be drilled with diameters even smaller than the wavelength of the laser. Some examples are presented in the paper.

An experimental and theoretical investigation of ultrashort pulse damage thresholds of Si and Ge semiconductors has been carried out. As the source of laser radiation, a commercial sub picosecond Ti:Sapphire laser system has been used. It produces laser pulses of 0.5 mJ pulse energy at 1 kHz repetition rate at a wavelength of 775 nm, providing a Gaussian-like beam profile. Compressor tuning allowed for varying the pulse duration from 150 fs to 5.5 ps. The laser damage thresholds were measured in air and for this pulse duration range. The experimental results supported for both materials an asymptotic temporal behaviour in the sub picosecond regime. For 200 fs pulses, a threshold of 0.17 J/cm^2 and 0.10 J/cm^2 was found for Si and Ge, respectively. The results of our theoretical description for Si were consistent with the experimental findings. The damage morphologies were investigated with various microscopic inspection techniques like Nomarski DIC, atomic force and white light inte...

Die Resistenz optronischer Komponenten gegen hochintensive Laserstrahlung ist in der Wehrtechnik und auch im zivilen Bereich von zunehmender Bedeutung. Untersuchungen zur Strahlungsschädigung optronischer Komponenten erfolgen am Institut für Technische Physik im Hinblick auf die spätere Verwendung der entsprechenden Komponenten und unter Berücksichtigung internationaler Standards der Zerstörschwellenmessung. Neben der Bestimmung von Schädigungsschwellen werden auch Schädigungsmorphologie und die zugehörigen Prozesse analysiert. Insbesondere der Einsatz eines Ultrakurzpulslasers ermöglichte die experimentelle Untersuchung des zeitlichen Skalierungsverhaltens der Schädigungsschwellen von kristallinem Ge und Si im Small-Spot Verfahren (1 / 1; s / 1). Als Laserquelle wurde ein kommerzieller Ti:Saphir Laser eingesetzt, dessen Pulsdauer im Bereich von 150 fs – 5.5 ps variiert werden konnte. Bei beiden Materialien konnte ein asymptotisches Verhalten bei Verkürzung der Pulse festgestellt we...

Based on two versions of Maxwell's Equations we investigate the Poynting vector, the energy transport and the dispersion relation both for right-and left-handed systems. Furthermore, it is shown that the latter systems are necessarily dispersive in contrast to the former ones. In the end we discuss a published example where the mixing of expressions of both versions of Maxwell's Equations leads to unphysical conclusions. The presentation demonstrates for students how flexible can be the work with different versions of electrodynamics but also how carefully one has to be thereby.

A model is proposed describing the interaction of short laser pulses with metals. It is shown that a generalized nonlocal heat flow in time leads to an equation of heat conduction with additional terms involving the time derivative of both the laser intensity and the coupling of the electrons to the phonons. The importance of the coefficient of heat exchange for the temperature distribution in metals and the different influence of its main parts, the electron phonon coupling and the averaged square phonon frequencies, is pointed out. For a laser pulse length of I ps the electron and phonon surface temperatures for Al, Cu. Nb and Pb are evaluated using a double temperature model with a nonlocal heat flow. This is compared with the results of a local heat flow approach and with the conventional theory.

In this paper, we report on the growth of high quality GaN films by a laser assisted process, optimized for the growth of epitaxial nitrides. Growth mode and film thickness were controlled in situ by the measurement of infrared-radiation Ž. transmission intensity IR-RTI oscillations. In the case of a light absorbing film, these oscillations are damped. A model is presented to fit the experimental data and to determine the free carrier concentration during deposition. Comparison with Ž. room temperature RT values from Hall measurements showed a satisfying agreement.