2017, Obst, Lieselotte, Göde, Sebastian, Rehwald, Martin, Brack, Florian-Emanuel, Branco, Joao, Bock, Stefan, Bussmann, Michael, Cowan, Thomas E., Curry, Chandra B., Fiuza, Frederico, Gauthier, Maxence, Gebhardt, Rene, Helbig, Uwe, Huebl, Axel, Hübner, Uwe, Irman, Arie, Kazak, Lev, Kim, Jongjin B., Kluge, Thomas, Kraft, Stephan, Löser, Markus, Metzkes, Josefine, Mishra, Rohini, Rödel, Christian, Schlenvoigt, Hans-Peter, Siebold, Mathias, Tiggesbäumker, Josef, Wolter, Steffen, Ziegler, Tim, Schramm, Ulrich, Glenzer, Siegfried H., Zeil, Karl

We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.

2020, Boni, Anisuzzaman, Wünsche, Hans-Jürgen, Wenzel, Hans, Crump, Paul

Electrons and holes injected into a semiconductor heterostructure containing quantum wellsare captured with a finite time. We show theoretically that this very fact can cause a considerableexcess contribution to the series resistivity and this is one of the main limiting factors to higherefficiency for GaAs based high-power lasers. The theory combines a standard microscopic-basedmodel for the capture-escape processes in the quantum well with a drift-diffusion description ofcurrent flow outside the quantum well. Simulations of five GaAs-based devices differing in theirAl-content reveal the root-cause of the unexpected and until now unexplained increase of theseries resistance with decreasing heat sink temperature measured recently. The finite capturetime results in resistances in excess of the bulk layer resistances (decreasing with increasingtemperature) from 1 mΩ up to 30 mΩ in good agreement with experiment.