Observation of forward propagating THz mode emitted from a two-color laser-induced air plasma
Knowledge about the spatial properties of the optical beam is important for most free-space optical experiments including THz spectroscopy and imaging. THz generation from a two-color laser-induced air plasma is a new, but already well-described technique for generation of broadband THz light [1, 2]. However, the spatial properties of the THz beam emitted from the plasma have not until recently been investigated in detail [3, 4]. Off-axis conical THz emission has both been predicted theoretically [5, 6] and demonstrated experimentally [3, 4, 5, 6, 7], but also an on-axis forward propagating component of the THz emission has been suggested [4, 6]. In this letter we report an experimental observation of this weak forward propagating THz mode by spatially eliminating the much stronger off-axis conical THz emission. The characteristics of this additional THz beam component emitted from the plasma are important for the understanding of the ultrafast dynamics in the plasma, as well as in a...
KeywordsIntensity Image Vertical Projection Conical Emission Effective Focal Length Borate Crystal