Temporal and Spatial Characterization of Ultrafast Terahertz Near-Fields for Particle Acceleration

Abstract

Terahertz generation by optical rectification in LiNbO 3 using the tilted pulse front method is a powerful technique that is routinely used to generate THz pulses with energies in the tens of micro-joules and field strengths above 1 MV/cm. THz-frequency accelerating structures that utilize these fields could provide the accelerating gradients needed for next generation particle accelerators with compact, GV/m-scale devices. However, accelerator applications are limited by significant losses during transport of THz radiation from the generating nonlinear crystal to the acceleration structure. In addition, the spectral properties of high-field THz sources make it difficult to couple THz radiation into accelerating structures. A better understanding of the THz near-field source properties and how they are affected by changes in the generation setup is necessary for the optimization of THz transport and coupling. We demonstrate a technique for robust spatial and temporal characterization of single cycle strong field THz pulses in the near-field of a LiNbO 3 source using electro-optic sampling. Using this technique we have reconstructed the full temporal 3D THz near-field close to the LiNbO 3 emission face. Our results will help to inform designs of novel structures for use in THz time domain spectroscopy, THz particle acceleration, and ultrafast beam manipulation.