Abstract-Coherent Transition Radiation from Relativistic Beam-Foil Interaction in the Terahertz and Optical Range

W. J. Ding, F. Y. Li, S. M. Weng, P. Bai, Z. M. Sheng

https://arxiv.org/abs/1902.04716

Coherent transition radiation (CTR) from relativistic electron beam interaction with an overdense plasma foil is investigated by making use of two-dimensional particle-in-cell simulations. Well-defined single electron beam either of uniform profile or having substructures is considered for various beam-plasma parameters. The main purpose is to mimic the complicated beam-plasma conditions that is often found, for example, in intense laser plasma interactions. Key properties of the CTR concerning their temporal, angular and spectral profiles are identified. Several saturation effects due to the beam energy, size and foil density are found for the CTR energy, and the dependences vary for different spectral components such as in the Terahertz (THz) and optical range. The detailed substructure of the beam also affects greatly the radiation generation, leading to distinctive high harmonic components. Electrons with kinetic energy from sub MeV to tens of GeV are explored. For few MeV electron beams, the effects of the foil plasma on the beam dynamics and associated CTR generation, resembles closely the CTR from hot electrons produced in intense laser-plasma interactions. These results may find important applications in beam diagnostics either in laser-plasma based acceleration or conventional accelerators. They may also be employed to design novel THz radiation sources using tunable electron beams.

Abstract-Below gap optical absorption in GaAs driven by intense, single-cycle coherent transition radiation

J. Goodfellow, M. Fuchs, D. Daranciang, S. Ghimire, F. Chen, H. Loos, D. A. Reis, A. S. Fisher, and A. M. Lindenberg  »View Author Affiliations

Optics Express, Vol. 22, Issue 14, pp. 17423-17429 (2014)
http://dx.doi.org/10.1364/OE.22.017423

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-14-17423

Single-cycle terahertz fields generated by coherent transition radiation from a relativistic electron beam are used to study the high field optical response of single crystal GaAs. Large amplitude changes in the sub-band-gap optical absorption are induced and probed dynamically by measuring the absorption of a broad-band optical beam generated by transition radiation from the same electron bunch, providing an absolutely synchronized pump and probe geometry. This modification of the optical properties is consistent with strong-field-induced electroabsorption. These processes are pertinent to a wide range of nonlinear terahertz-driven light-matter interactions anticipated at accelerator-based sources.

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