Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the laser light to the material properties for optimal processing quality. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss and cooling mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to efficient material removal and reduction of the residual damage. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show, that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.
A significant improvement in the quality of ultrafast laser micromachining of brittle dielectrics is demonstrated by using temporally shaped pulse trains with sub-ps separation, synchronized with the material specific relaxation times. The individual material response to laser radiation depends on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to the efficiency of material removal and reduction of the residual damage. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process.
Dielectric materials exposed to ultrashort laser radiation have evidenced individualized paths to deposit the energy into the lattice. Electronic and thermal mechanisms competing in the process of material removal depend on the efficiency of the electrostatic energy accumulation on the surface due to photoionization, as well as on the lattice heating which follows the electron-phonon coupling. The electrostatic surface break-up is a fast, sub-picosecond process, while thermal mechanisms start to dominate on a longer, picosecond time scale given by the electron-lattice equilibration and phase transformation time. The Coulomb- explosion induced ion ejection due to surplus charge accumulated on the surface during the photoionization process is significant only in dielectrics while in semiconductors and metals an efficient neutralization occurs. The significance of the different channels in dielectric materials can be reduced or enhanced by using laser pulses which are modulated on a time scale characteristic for the above mentioned mechanisms. Thus, amplified temporally-shaped pulses, double peaks, or pulse trains with a separation below 1 ps can have a significant effect on the quality of micromachining of transparent materials. The energy deposition can be modulated in such a way that the first pulse of properly chosen energy leads to a softening of the material associated with the onset of heating, thus changing the coupling conditions for the next pulses. This leads to less residual stress accumulation, cleaner structures, and opens the way for a material dependent optimization process.
WS1134: Effective Scientific Writing
Whether you are starting or established - successful publishing is crucial for any scientist's career. This course is intended as an introduction into all the elements that, in the end, make a great scientific paper. You will learn the basics of scholarly communication followed by lessons on structuring a paper, proper use of English and new ways of publishing. You will get insights to bibliometric tools and learn how to find the right platform for your publication among Open Access platforms, conventional journals and B2B-magazines. Textbooks for further reading will also be recommended.