Conical versus Gaussian terahertz emission from two-color laser-induced air plasma filaments
Résumé
We demonstrate that the far-field terahertz beam generated from a Ti:Sapphire two-color laser-induced filament can exhibit a conical or Gaussian distribution depending on the filtering experimental conditions. Using both an incoherent Golay cell detector and a twodimensional coherent electro-optic detection covering the 0.2-3 THz spectral range, in our experimental conditions, we provide evidences that the conical emission is due to photoinduced carriers in the silicon filter typically used to block the remaining pump laser light. Moreover, the terahertz beam retrieves an almost TEM 00 Gaussian spatial distribution when the silicon filter is preceded by a large bandgap ceramic filter, which stops the pump beam preventing carriers generation in the silicon filter.
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