Abstract-Optimization of carrier density in graphene via terahertz pulse shaping

Denis Gagnon, Joey Dumont, François Fillion-Gourdeau, Steve MacLean

(Submitted on 26 Oct 2017)

https://arxiv.org/abs/1710.09889

Pulse shaping calculations for the control of photo-excited carrier densities in graphene are presented. A spectral parametrization of the incident pulse using B-splines is used in order to obtain experimentally realistic pulses of bandwidth ∼ 3 THz. Optimization of the spectral shape is performed numerically via differential evolution, using the B-splines expansion coefficients as decision variables. Using this high-level optimization procedure, we find that it is possible to change the carrier density in graphene by a factor of 4 for a fixed pulse energy. The selective suppression of multi-photon absorption features in reciprocal space is also discussed, as well as the application of this theoretical work to the control of scattering mechanisms in graphene.

Abstract-Terahertz pulse shaping through propagation in a gas of symmetric top molecules

K. Hamraoui, P. Babilotte, F. Billard, E. Hertz, O. Faucher, L. H. Coudert, D. Sugny, and B. 
Lavorel

https://journals.aps.org/pra/accepted/35076NdeR1b1dc1467c928231c6a30bb745e593d5

Symmetric-top molecules of methyl iodide are irradiated with a terahertz pulse generated by a two-color plasma and shaped by a short propagation in air. A free-induction decay is emitted by the excited molecular sample and then propagates in air before detection. The experimental data show that the input terahertz pulse undergoes strong reshaping through absorption and dispersion. This leads to narrow wave packets at revival times due to the excitation of high rotational energy levels. Typically a THz burst of duration \simeq 15-20 ps is produced periodically, with a central frequency of \simeq 1 THz and a width that can be as narrow as 60--80 GHz. Pulse shaping based on propagation can be useful for quantum control in molecules. We provide a theoretical description of this wave propagation based on the Maxwell-Bloch equation. The observed experimental signal is in good accordance with the numerical simulations.