Surface structuring by remelting with laser radiation is a new approach to shape metallic surfaces (“WaveShape”). In this structuring process, surface material is reallocated in its molten state instead of being removed, because the process is based on the new active principle of remelting. The surface structure and the microroughness result from a laser-controlled melt pool due to surface tension. Basic research has been conducted with promising results, especially for the hot work steel 1.2343. Since remelting is a thermally driven process, significant differences between metallic materials were expected due to their thermophysical properties such as thermal conductivity, absorption coefficient, viscosity, heat capacity, etc. Therefore, the presented research soughed to expand the spectrum of processable materials. Within the framework of our investigation, we compared the achieved structure height as well as melt pool dimensions for six different materials. Furthermore, we successfully tested new structuring strategies such as not linearly shaped scanning vectors to create innovative surface structures on all materials investigated. The biggest structures were achieved on the titanium alloy Ti6Al4V and the nickel based super alloy IN718. Finally, an approach of reverse structuring was investigated in order to erase existing structures and achieve a smoothed rewriteable metallic surface. The results show that surface structuring by laser remelting is well suited to process a wide range of different metals and to achieve a broad variety of different structures as well as to effectively erase existing surface structures such as milling marks.

We present significantly improved performance data of a diode-pumped $Q$-switched Alexandrite laser in single longitudinal mode operation developed as a beam source for resonance lidar systems. The average output power of the laser—operating at the potassium resonance at 770 nm with a linewidth below 10 MHz—could be increased by a factor of five to the Watt-level by means of an optimized resonator design and pump scheme. The pulse energy is 1.7 mJ with a beam quality of ${\mathrm{M}}^2\le 1.1$ in both spatial directions at a repetition rate of 500 Hz.

We present the design of a longitudinally diode-pumped Alexandrite laser in continuous-wave operation and resulting performance data. A laser power of 6.5 W in fundamental mode operation was measured, which is, to the best of our knowledge, the highest laser power in fundamental mode operation yet reported. The laser crystal was pumped by two diode modules emitting at 637 nm. The pump radiation was polarization-combined and spatially symmetrized. The laser operates at an output power of 6.5 W with an optical-to-optical efficiency of 26%, temporally stable output with stability of 8% on ms timescale, a beam quality of M-2 = 1.1 in both spatial directions and emission of an output wavelength of 752 nm. Measurements of the thermal dioptric power at pumping intensities up to 9.5 kW/cm(2) support the appropriate approach of the design. Based on our results, we estimate the potential and show our concept for future scaling of the output power. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Converting single photons from one wavelength to another is of fundamental interest for future quantum communication and computing. Using commercially available lasers and a multimode PPLN waveguide a DFG scheme was set up. Phase-matching was shown in the fundamental transverse mode of the waveguide for wavelengths between 851 nm and 862 nm. The setup is capable of converting up to 87% of photons from 856 nm to 1526 nm in transverse fundamental mode. Simulations were performed showing that the quantum conversion efficiency at 856 nm is representative for powers down to thousands of photons per second.