Abstract

Terahertz (THz) sources have attracted an increasing interest for applications in time-domain spectroscopy and security screening for many years [1]. Recently, two-color laser filaments were reported to be efficient tools for the remote generation of THz radiation over long distances in gases [2]. Despite numerous experimental results, there is, however, no clear understanding of the dominant physical mechanism driving THz generation in filamentation regime, i.e., either rectification by four-wave mixing (FWM) or plasma currents generated by tunnel ionization. Here, we examine THz generation by two-color filamentation in argon by means of fully three-dimensional (3D) numerical simulations for different pump pulse energies, durations and central wavelengths. Evaluating the THz spectra from either Kerr or plasma sources reveals that photocurrents are dominant in THz generation during filamentation at clamping intensity. Our numerical results reproduce several experimental features, such as the growth of the THz yield with the pump pulse energy or with the pulse duration.

© 2013 IEEE