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- ItemGeneration of millijoule few-cycle pulses at 5 μm by indirect spectral shaping of the idler in an optical parametric chirped pulse amplifier(Washington, DC : Soc., 2018) Bock, Martin; Grafenstein, Lorenz von; Griebner, Uwe; Elsaesser, ThomasSpectral pulse shaping in a high-intensity midwave-infrared (MWIR) optical parametric chirped pulse amplifier (OPCPA) operating at 1 kHz repetition rate is reported. We successfully apply a MWIR spatial light modulator (SLM) for the generation of ultrashort idler pulses at 5 μm wavelength. Only bulk optics and active phase control of the 3.5 μm signal pulses via the SLM are employed for generating compressed idler pulses with a duration of 80 fs. The 80-fs pulse duration corresponds to less than five optical cycles at the central wavelength of 5.0 μm. The pulse energy amounts to 1.0 mJ, which translates into a peak power of 10 GW. The generated pulse parameters represent record values for high-intensity MWIR OPCPAs.
- ItemThe thermal stability of epitaxial GeSn layers(Melville, NY : AIP Publ., 2018) Zaumseil, P.; Hou, Y.; Schubert, M.A.; von den Driesch, N.; Stange, D.; Rainko, D.; Virgilio, M.; Buca, D.; Capellini, G.We report on the direct observation of lattice relaxation and Sn segregation of GeSn/Ge/Si heterostructures under annealing. We investigated strained and partially relaxed epi-layers with Sn content in the 5 at. %-12 at. % range. In relaxed samples, we observe a further strain relaxation followed by a sudden Sn segregation, resulting in the separation of a β-Sn phase. In pseudomorphic samples, a slower segregation process progressively leads to the accumulation of Sn at the surface only. The different behaviors are explained by the role of dislocations in the Sn diffusion process. The positive impact of annealing on optical emission is also discussed.