Directional intense terahertz radiation driven by abruptly autofocusing lasers in air
arxiv(2024)
摘要
Two-color laser induced plasma filamentation in air could serve as tabletop
sources of broadband terahertz (THz) pulses. Ubiquitous air in the earth
facilitates its widespread utilities, particularly, in wireless communication
and remote sensing, exploiting the unique advantage of the air-based scheme
that the THz sources can be delivered over standoff distances via the pump
laser propagation in air. However, the THz emission pattern inevitably has a
conical angular profile with a dip in the propagation axis, therefore, THz
energy concentration, propagation directionality, and accuracy of signal
demodulation are significantly impaired, greatly limiting its direct
applications. Here, we successfully eliminate the unfavorable conical profile
by experiments and meanwhile enhance THz directionality and intensity by 17
folds by use of abruptly-autofocusing laser beams. Our theory and simulations
show that these observations are attributed to efficient suppression of the
dephasing effect appearing in previous investigations with ordinary Gaussian
laser beams. This scheme is easily accessible since the abruptly-autofocusing
beam can be achieved by imposing a spatial light modulator on the input
Gaussian beam. This study solves a long-standing problem in the two-color laser
scheme and clarifies the underlying physics of the conical angular profile
formation.
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