We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaBO (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 g without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.
Cooling and detection schemes using laser cooling and methods of quantum logic can contribute to high precision CPT symmetry tests in the baryonic sector. This work introduces an experiment to sympathetically cool protons and antiprotons using the Coulomb interaction with a 9 Be + ion trapped in a nearby but separate potential well. We have designed and set up an apparatus to show such coupling between two identical ions for the first time in a Penning trap. In this paper, we present evidence for successful loading and Doppler cooling of clouds and single ions are presented. Our coupling scheme has applications in a range of high-precision measurements in Penning traps and has the potential to substantially improve motional control in these experiments.
The finite element method is a powerful tool for the design and optimization of hot forming processes. In order to obtain high accuracy in simulation results, exact knowledge of the process conditions is required. Due to the fact that friction in the contact area has a significant impact on the material flow during the forming process, a realistic description of this boundary condition in the FE simulation is important for the usability of the simulation results. The most important influencing factors are the contact pressure, the roughness of the contact surfaces, the sliding velocity and the flow behavior of the material. Currently, only constant friction coefficients are considered in commercial finite element systems for the simulation of bulk metal forming processes. However, this description does not represent the state of the art in tribology. A new friction model is developed, taking into account the sliding velocity between tools and workpiece. This is confirmed by experimental and numerical investigations on model experiments and industrial process.
In hot forging processes the complex heat transfer and friction conditions are significantly influenced by the local effects occurring at the contact interface between the tool and workpiece. These effects basically include the prevailing normal stress and shear yield stress of the workpiece material, the temperature and surface roughness of the tool and workpiece as well as the relative sliding velocity. Hence, these effects were considered for the extension of the heat transfer and friction models. Two representative forging tests were carried out; the forming load and surface temperature distribution were recorded. By means of this data, the models were appropriately extended and adjusted using the software FORGE ®. The application of the extended models allows for a more accurate description of the interaction at the contact interface. Thus FE computations of hot forging processes deliver more realistic results.
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