Ring and unimodal angular-frequency distribution of THz emission from two-color femtosecond plasma sparkстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Аннотация:We study angular and frequency-angular distributions of the terahertz (THz)
emission of the low-frequency region (0.3–3 THz) from a two-color femtosecond plasma
spark experimentally and in three-dimensional numerical simulations. We investigate the
dependence of the angular shapes of the THz radiation on focusing conditions and pulse
durations by using two laser facilities (pulse durations 35 and 150 fs) for different focusing
geometries. Our experiments and simulations show that decrease in the numerical aperture
from NA ≈0.2 to NA ≈0.02 results simultaneously in (I) squeezing of the THz angular
distribution and (II) formation of the bright conical emission in the THz range. The moderate
focusing NA ≈0.05, which forms the relatively narrow unimodal THz angular distribution, is
identified as optimal in terms of angular divergence. Numerical simulations with carrier wave
resolved show that bright THz ring structures appear at the frequencies ≥ 2 THz for longer
focuses (NA ≈0.02), while for optimal focusing conditions NA ≈0.05 the conical emission
develops at THz frequencies higher than 10 THz.