Abstract-Terahertz Pulse Generation in Underdense Relativistic Plasmas: From Photoionization-Induced Radiation to Coherent Transition Radiation

J. Déchard, A. Debayle, X. Davoine, L. Gremillet, and L. Bergé

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.144801

Terahertz to far-infrared emission by two-color, ultrashort optical pulses interacting with underdense helium gases at ultrahigh intensities ($>{10}^{19}W/{\mathrm{cm}}^2$) is investigated by means of 3D particle-in-cell simulations. The terahertz field is shown to be produced by two mechanisms occurring sequentially, namely, photoionization-induced radiation (PIR) by the two-color pulse, and coherent transition radiation (CTR) by the wakefield-accelerated electrons escaping the plasma. We exhibit laser-plasma parameters for which CTR proves to be the dominant process, providing terahertz bursts with field strength as high as $100\mathrm{GV}/m$ and energy in excess of 10 mJ. Analytical models are developed for both the PIR and CTR processes, which correctly reproduce the simulation data.

• 
• 
• 
• 

Abstract-Sequential terahertz pulse generation by photoionization and coherent transition radiation in underdense relativistic plasmasp

J.Déchard, A. Debayle, X. Davoine, L. Gremillet, L. Bergé

(Submitted on 14 Sep 2017)

https://arxiv.org/abs/1709.04639

Terahertz (THz) emission by two-color, ultrashort optical pulses interacting with underdense helium gases at ultrahigh intensities (>1019W/cm2) is investigated by means of 3D particle-in-cell simulations. The THz field is shown to be produced by two mechanisms occurring sequentially, namely, photoionization-induced radiation (PIR) by the two-color pulse and coherent transition radiation (CTR) by the wakefield-accelerated electrons escaping the plasma. For plasmas of atomic densities >1017cm−3, CTR proves to be the dominant process, providing THz bursts with field strength as high as 100GV/m and energy in excess of 1mJ. Analytical models are developed for both the PIR and CTR processes, which correctly reproduce the simulation data.

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.