In the recent years high-power laser beams with radial polarization have attracted an increasing interest because of their
interesting properties in material processing. We present an overview of the current activities and different techniques to
generate such beams in CO<sub>2</sub> and solid-state lasers. With a polarising end-mirror which comprises a resonant grating on a
dielectric multilayer Bragg-structure we recently demonstrated a 3-kW radially polarised CO<sub>2</sub> laser. Current
investigations are also focused especially on the application of this technology to thin-disk lasers. The specific
requirements and the whole development from the design and fabrication to the characterization and test are illustrated
with the example of a multilayer polarizing grating mirror developed to generate a radially polarised beam in an
Yb:YAG thin-disc laser resonator. The potential of this kind of beams are discussed with a number of first application
results, which largely confirm the predictions presented by Niziev et al1.
Drilling holes with pulsed Nd:YAG lasers is well researched and state-of-the-art within a variety of industrial applications. Surgical needles in the medical field, turbine blades for the aviation industry, and gas filter for the automotive industry are just some examples that come to mind. Similar to other industrial developments over the last century this market asks for higher throughput, smaller diameter, higher aspect ratios, and of course within a minimum of tolerances. New laser sources and specially developed processes are entering the market to move the mere drilling to the next level of micro drilling. It is crucial to understand the application and the influence of the process parameters to develop a suitable, stable, and repeatable work process. Commonly used pulses within the microsecond-regime show a significant thermal side effect which is unacceptable if used e.g. in combustion nozzles. Reducing the thermal load by shortening the pulse length into the nanosecond-regime could be a compromise to bridge the gap between quality and production speed in high precision laser drilling. However, depending on the relation between pulse energy, pulse repetition rate, and "helical speed" a reduced, but existent, thermal effect is inevitable. The scope of this paper is to show the influences of the process parameters in helical drilling with a new developed nanosecond pulsed Nd:YAG laser at its fundamental wavelength of 1064 nm. A variation of drilling-optic principles in different materials are studied and the advantages as much as the disadvantages are discussed.
Radially polarized radiation shows some very interesting properties and has therefore gained interest in recent years. An overview of the advantages and the various applications where radially polarized modes are beneficial is given. In addition the different known methods to generate radial polarization are reviewed. In our work we developed a method to generate radially polarized laser beams by means of a polarization selective resonant grating mirror. The undesired polarization is coupled to a mode of the dielectric multilayer of the resonator end mirror and experiences severe losses while the radial polarization is not affected and oscillates in the laser resonator. Fundamental and higher-order radially polarized modes of high polarization purity and powers of more than 100W have been demonstrated.