Ultrashort pulse lasers have been established as precise and universal tools for the micromachining of solid materials (cutting, texturing …). For these applications the quality of the cutting cross-section is important. The use of a Gaussian beam profile and linear polarization leads to tapered cutting sidewalls. It is possible to change the polarization orientation in order to machine a material for obtaining straight and vertical sidewalls. For this purpose a specific polarization converter was used. The transformation of the polarization distribution from linear to radial and azimuthal is done by a subwavelength, binary grating creating a π phase shift between the TE and TM transmitted waves. In this paper we report on investigations on the influence of laser polarization (radial, azimuthal, circular, linear) on the ablation characteristics of molybdenum and PZT using an Yb doped crystal laser (500 fs) and compare these results with previously published results.

In this study, we worked on the formation of micro through holes in multi-component glass substrates using laser-assisted etching, in which mixed aqueous solutions of hydrofluoric acid (HF) and nitric acid (HNO 3 ) were used for the etching. Glass samples modified by femtosecond laser irradiation were immersed for 10 minutes in aqueous solutions containing 2% HF and between 0 and 32% HNO 3 . The subsequent optical microscope observations and measurements showed that the highest etch selectivity, which was 21, was obtained with an etch solution containing 6% HNO 3 . Furthermore, through holes with diameters approaching 20 μm were successfully formed in a 100 μm thick glass substrate without any cracks using the mixed solution.

A compact tunable waveplate based on negative dielectric liquid crystal photonic bandgap fibers is presented. The birefringence can be tuned electrically to work as a quarter-wave or a half-wave plate in the wavelength range 1520nm-1580nm.

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We describe two test benches that were designed and constructed to perform a set of acceptance tests for about 1200 Photomultiplier Tube (PMT) units to be installed in the surface scintillation detectors of AugerPrime. Besides possessing robustness, long-term reliability, and low power consumption, each PMT-unit requires a dynamic range wide enough to cover signals ranging from a single to more than 20,000 minimum ionizing particles with not more than 5 % deviation from linear response. This posed a particular challenge which was met by combining a specially selected 1.5" PMT type with a custom made Cockcroft Walton type base. The characteristics of the PMT units and qualification results obtained for a large quantity of tested units will be presented and discussed. Besides measuring the gain and linearity for each PMT-unit for different supply voltages, in a sub-sample of about 10 %, we also measured the quantum-efficiency of the photocathode as a function of wavelength as well as its homogeneity across the full photocathode area with 1 mm spatial resolution. The latter is of importance because of the fiber-optical readout of the scintillation detectors.