Optimum Pulse Duration for THz Yield from the Air-Based Plasma

Among the terahertz (THz) sources, a two-color femtosecond filament in gases provides the coherent THz emission with the most broadband spectrum, which spans up to several tens of THz. Optical to terahertz conversion efficiency in the gas-based plasma reaches ~0.01% for the near infrared (800+400 nm) or up to 1% for the mid-infrared pump [1]. By positively chirping the initial pulse, one can increase the optical to THz conversion efficiency by an order of magnitude [2]. The THz yield depends strongly on the relative phase between the fundamental and the 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> harmonic radiation. Recently it was found that the relationship between THz pulse energy and chirp changes with variations in the specific phase difference between the first and second harmonics, and that the maximum THz energy might be attained not only for positively, but also for the negatively chirped pulse [3].