Abstract

Over the past decade, the increasing potential of terahertz (THz) radiation has stimulated intensive efforts to develop efficient emitters based on the ionization of gases by ultrashort laser pulses [1]. In order to properly calibrate dedicated experiments, nonlinear propagation codes have to be particularly accurate to describe the low-frequency part of the pulse spectrum. Usually, solving full Maxwell models accounting for multiple ionization processes as well as optical and plasma nonlinear effects is computationally expensive when simulating long propagation ranges. Therefore, reduced models such as the Unidirectional Pulse Propagation Equation (UPPE) [2] are often preferred, assuming that the forward propagating component conveys the major part of the laser energy. So far, no detailed numerical comparison has been performed to confirm the validity of this UPPE approach, which is widely used in the scope of laser-driven THz generation [3]. Here, we examine by means of 1D simulations the differences occurring in the THz pulse spectra and fields when these quantities are described either by a full Maxwell-fluid (MAXFLU) model, encompassing both backward and forward propagations, or by its UPPE approximation, modeling only the forward propagating wave.

© 2017 IEEE