Zhihui Lü, Dongwen Zhang, Chao Meng, Xiyu Du, Zhaoyan Zhou, Yindong Huang, Zengxiu Zhao and Jianmin Yuan
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zhao.zengxiu@gmail.com jmyuan@nudt.edu.cn
Department of Physics, National University of Defense Technology, Changsha 410073, People's Republic of China
Department of Physics, National University of Defense Technology, Changsha 410073, People's Republic of China
Argon atom ionizing in the ultrafast two-colour field has been used to investigate the physical mechanism of terahertz (THz) generation. We measured simultaneously pulse energies of THz and high-harmonics as the phase delay between the fundamental and its second harmonic was varied. The optimal phase delay of THz generation is determined according to the inherent attochirp of the emitted high-harmonics. The dynamic analysis of the tunnelling electron wave packet driven by the Coulomb–laser coupling shows that laser-assisted soft collisions of the electron wave packet with the atomic core play a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way.
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