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Terahertz radiation driven by two-color laser pulses at near-relativistic intensities: Competition between photoionization and wakefield effects
Author(s) -
Pedro González Martínez,
Xavier Davoine,
A. Debayle,
L. Grémillet,
Luc Bergé
Publication year - 2016
Publication title -
scientific reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.24
H-Index - 213
ISSN - 2045-2322
DOI - 10.1038/srep26743
Subject(s) - photoionization , physics , atomic physics , laser , ionization , plasma , terahertz radiation , ponderomotive force , transverse plane , photocurrent , electron , femtosecond , optics , ion , nuclear physics , quantum mechanics , structural engineering , engineering
We numerically investigate terahertz (THz) pulse generation by linearly-polarized, two-color femtosecond laser pulses in highly-ionized argon. Major processes consist of tunneling photoionization and ponderomotive forces associated with transverse and longitudinal field excitations. By means of two-dimensional particle-in-cell (PIC) simulations, we reveal the importance of photocurrent mechanisms besides transverse and longitudinal plasma waves for laser intensities >10 15  W/cm 2 . We demonstrate the following. (i) With two-color pulses, photoionization prevails in the generation of GV/m THz fields up to 10 17  W/cm 2 laser intensities and suddenly loses efficiency near the relativistic threshold, as the outermost electron shell of ionized Ar atoms has been fully depleted. (ii) PIC results can be explained by a one-dimensional Maxwell-fluid model and its semi-analytical solutions, offering the first unified description of the main THz sources created in plasmas. (iii) The THz power emitted outside the plasma channel mostly originates from the transverse currents.

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