2021, Schröder, Mirjam, Rauber, Daniel, Matt, Clemens, Kay, Christopher W. M.

Testing and calibrating an experimental setup with standard samples is an essential aspect of scientific research. Single crystals of pentacene in p-terphenyl are widely used for this purpose in transient electron paramagnetic resonance (EPR) spectroscopy. However, this sample is not without downsides: the crystals need to be grown and the EPR transitions only appear at particular orientations of the crystal with respect to the external magnetic field. An alternative host for pentacene is the glass-forming 1,3,5-tri(1-naphtyl)benzene (TNB). Due to the high glass transition point of TNB, an amorphous glass containing randomly oriented pentacene molecules is obtained at room temperature. Here we demonstrate that pentacene dissolved in TNB gives a typical “powder-like” transient EPR spectrum of the triplet state following pulsed laser excitation. From the two-dimensional data set, it is straightforward to obtain the zero-field splitting parameters and relative populations by spectral simulation as well as the B1 field in the microwave resonator. Due to the simplicity of preparation, handling and stability, this system is ideal for adjusting the laser beam with respect to the microwave resonator and for introducing students to transient EPR spectroscopy. © 2021, The Author(s).

2021, Davenport, John J., Diab, Momen, Deka, Pranab J., Tripathi, Aashana, Madhav, Kalaga, Roth, Martin M.

We present a detailed method of tapering and drawing photonic lanterns using a filament glass processing system. Single-mode fibers (SMFs) were stacked inside a low refractive index, fluorine-doped capillary, which was then heated and tapered to produce a transition from single-mode to multi-mode. Fabrication parameters were considered in four categories: method of preparation and stacking of SMFs into a capillary, heat and filament dimensions of the glass processor, capillary ID, and the use of vacuum during tapering. 19- and 37- fiber lanterns were drawn, demonstrating good fusion between SMF claddings, a clear differentiation between core and cladding in the multimode (MM) section, and well-ordered arrangements between SMFs, which is controlled during the tapering process. The transmission efficiency of a 19-fiber photonic lantern, compared to an MMF with the same core diameter and NA, has a relative transmission efficiency of 1.19 dB or 67.1%. The steps and parameters provided in this paper form a framework for fabricating quality photonic lanterns.

2020, Wegner, Th., Geiger, B., Foest, R., Jansen van Vuuren, A., Winters, V. R., Biedermann, C., Burhenn, R., Buttenschön, B., Cseh, G., Joda, I., Kocsis, G., Kunkel, F., Quade, A., Schäfer, J., Schmitz, O., Szepesi, T.

Coated glass targets are a key component of the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of these glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with μm thick films. In addition, nm-thin layers of Ti are used as an interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5%, being optimal for laser ablation processing. With this method, a short (few ms) and well defined pulse of impurities with about 1017 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with a velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X. © 2020 Author(s).