Wednesday, December 17, 2014
Tuesday, December 16, 2014
P. González de Alaiza Martínez, I. Babushkin, L. Bergé, S. Skupin, E. Cabrera-Granado, C. Köhler, U. Morgner, A. Husakou, J. Herrmann
(Submitted on 16 Dec 2014)
Broadband ultrashort terahertz (THz) pulses can be produced using plasma generation in a noble gas ionized by femtosecond two-color pulses. Here we demonstrate that, by using multiple-frequency laser pulses, one can obtain a waveform which optimizes the free electron trajectories in such a way that they reach the highest velocity at the electric field extrema. This allows to increase the THz conversion efficiency to the percent level, an unprecedented performance for THz generation in gases. Besides the analytical study of THz generation using a local current model, we perform comprehensive 3D simulations accounting for propagation effects which confirm this prediction. Our results show that THz conversion via tunnel ionization can be greatly improved with well-designed multicolor pulses.
J. Phys. Chem. A, Just Accepted Manuscript
Publication Date (Web): December 16, 2014
Copyright © 2014 American Chemical Society
N. Kamaraju, W. Pan, U. Ekenberg, D. M. Gvozdić, S. Boubanga-Tombet, P. C. Upadhya, J. Reno, A. J. Taylor, R. P. Prasankumar
We have used terahertz (THz) magneto-optical spectroscopy to investigate the cyclotron resonance in high mobility two-dimensional electron and hole systems. Our experiments reveal long-lived (~20 ps) coherent oscillations in the measured signal in the presence of a perpendicular magnetic field. The cyclotron frequency extracted from the oscillations varies linearly with magnetic field for a two-dimensional electron gas (2DEG), as expected. However, we find that the complex non-parabolic valence band structure in a two-dimensional hole gas (2DHG) causes the cyclotron frequency and effective mass to vary nonlinearly with the magnetic field, as verified by multiband Landau level calculations. This is the first time that THz magneto-optical spectroscopy has been used to study 2DHG, and we expect that these results will motivate further studies of these unique 2D nanosystems.