Abstract

In this Letter, we demonstrate that the far-field terahertz (THz) 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 two-dimensional coherent electro-optic detection covering the 0.2–2.6 THz spectral range, in our experimental conditions, we provide evidence that the conical emission is due to photo-induced carriers in the silicon filter, typically used to block the remaining pump laser light. Moreover, the low-frequency THz beam retrieves an almost $ {{\rm TEM}_{00}} $ Gaussian spatial distribution when the silicon filter is preceded by a large bandgap ceramic filter, which stops the pump beam, thus preventing the carrier generation in the silicon filter.

© 2020 Optical Society of America

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