Abstract-Multiple ionization events that non-monotonically increase laser-driven THz emissions

A. Debayle, P. González de Alaiza Martínez, L. Gremillet, and L. Bergé

https://journals.aps.org/pra/accepted/db073Ya2M8f1304801a5128200fd1e10a4fcaf694

Highly-charged states created through multiple ionization of gases are shown to enhance THz generation by intense, single- or two-color femtosecond laser pulses. A one-dimensional, non-propagating fluid model reveals the main conversion processes up to 1017\,\mathrm{Wcm}-2 laser intensities, namely, ionization-induced photocurrents and plasma current oscillations. For increasing intensities, we demonstrate a cyclic growth in the THz signal associated with the different binding energies of argon and helium. This behavior is confirmed by direct particle-in-cell and unidirectional pulse propagation simulations. Changes in the forward and backward THz spectra owing to multiple ionization are discussed.