Abstract
Over the past decade, the increasing potential of terahertz (THz) radiation in many societal areas has stimulated intensive efforts to develop efficient low-frequency sources based on nonlinear optics or laser-created plasmas. By letting an ultrashort laser field with one or several colors ionize a noble gas, intense THz pulses can be produced. For strong laser intensities between 1014 Wcm−2 and 1017 Wcm−2, the observed THz radiation has recently been explained by a 1D fluid-Maxwell model [1] and shown to be mainly triggered by two mechanisms: the plasma current oscillations and the ionization-induced photocurrents [2]. For practical applications a key issue is to understand how the THz pulse energy increases with the laser and material parameters. So far, most theoretical studies have considered either hydrogen or singly ionizable gas targets, while experiments routinely employ molecular or noble gases whose shell structures are not limited to one extractable electron. Here, we examine theoretically and numerically the dependence of the laser-driven THz radiation on the laser intensity in the context of multiple ionization of helium and argon for non-relativistic intensities up to 1017 Wcm−2.
© 2015 IEEE
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