Regensburg 2022 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 4: Semiconductor Lasers
HL 4.3: Vortrag
Montag, 5. September 2022, 10:00–10:15, H33
Field-resolved high-order sub-cycle nonlinearities in a terahertz quantum cascade laser — •Josef Riepl1, Jürgen Raab1, Pavel Abajyan2, Hanond Nong2, Joshua Freeman3, Lianhe H. Li3, Edmund H. Linfield3, A. Giles Davies3, Andreas Wacker4, Tim Albes5, Christian Jirauschek5, Christoph Lange6, Sukheep S. Dhillon2, and Rupert Huber1 — 1University of Regensburg, Germany — 2Université de Paris, France — 3University of Leeds, UK — 4Lund University, Sweden — 5Technical University of Munich, Germany — 6TU Dortmund University, Germany
Employing ultrafast electron dynamics in quantum cascade lasers (QCLs) holds enormous potential for intense, compact mode-locked terahertz (THz) sources, squeezed THz light, frequency mixers, and comb-based metrology systems. Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs. Here, we perform the first ultrafast two-dimensional high-field spectroscopy of a free running THz QCL. The detected strong incoherent and coherent nonlinearities up to eight-wave mixing do not only reveal extremely short gain recovery times, but also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time. A density-matrix approach reproducing all nonlinearities and their ultrafast evolution, allows us to map the coherently induced trajectory of the Bloch vector. The observed nonlinearities benefit from resonant enhancement in a regime of negative absorption and bear potential for various future applications, ranging from efficient intracavity frequency conversion and mode proliferation to passive mode locking.