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Start date: 2010 × DDC: 530 × Type: Text × Subject: Layered semiconductors × WGL Institute: MBI ×

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    Sub-cycle valleytronics: control of valley polarization using few-cycle linearly polarized pulses
    (Washington, DC : OSA, 2021) Jiménez-Galán, Álvaro; Silva, Rui E. F.; Smirnova, Olga; Ivanov, Misha
    So far, it has been assumed that selective excitation of a desired valley in the Brillouin zone of a hexagonal two-dimensional material has to rely on using circularly polarized fields. We theoretically demonstrate a way to control the valley excitation in hexagonal 2D materials on a few-femtosecond timescale using a few-cycle, linearly polarized pulse with controlled carrier–envelope phase. The valley polarization is mapped onto the strength of the perpendicular harmonic signal of a weak, linearly polarized pulse, which allows to read this information all-optically without destroying the valley state and without relying on the Berry curvature, making our approach potentially applicable to inversion-symmetric materials. We show applicability of this method to hexagonal boron nitride and MoS2.
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    Few-cycle 65-µJ pulses at 11.4 µm for ultrafast nonlinear longwave-infrared spectroscopy
    (Washington, DC : Optical Society of America, OSA, 2022) Fuertjes, Pia; Bock, Martin; Grafenstein, Lorenz von; Ueberschaer, Dennis; Griebner, Uwe; Elsaesser, Thomas
    Low-energy excitations can provide insight into the basic ultrafast nonequilibrium dynamics of condensed matter. High-energy femtosecond pulses in the long-wavelength infrared are required to induce such processes, and can be generated in an optical parametric chirped pulse amplification (OPCPA) system comprising three GaSe stages. A femtosecond Cr:ZnS laser serves as the front-end, providing the seed for the 2.0-µm pump and the 2.4-µm signal pulses without nonlinear conversion processes. The OPCPA system is pumped at 2.05 µm by a picosecond Ho:YLF regenerative amplifier at a 1-kHz repetition rate. The recompressed idler pulses at 11.4 µm have a duration of 185 fs and an unprecedented energy of 65 µJ, corresponding to a pump-to-idler conversion efficiency of 1.2%. Nonlinear transmission experiments in the range of the L2 infrared band of liquid water demonstrate the potential of the pulses for nonlinear vibrational spectroscopy of liquids and solids.