Ticking terahertz wave generation in attoseconds
  We perform a joint measurement of terahertz waves and high-order harmonics generated from noble atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase-delay of the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft-collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in HHG processes, dominant THz wave generation as well but in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics. 
Dongwen Zhang, Zhihui L\"u, Chao Meng, Xiyu Du, Zhaoyan Zhou, Zengxiu   Zhao, Jianmin Yuan
physics.atom-ph