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We perform a joint measurement of terahertz waves and high-harmonics generated from argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase delay between 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 high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics.

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The presented tooth segmentation method can be used to segment tooth contours from CT images accurately and efficiently.

Terahertz radiation from tunneling ionization of gaseous atoms and molecules in the two-color laser fields with various polarizations has been investigated. We experimentally demonstrate that the efficiency of terahertz emission in the circularly polarized laser fields with the same helicity is 5 times higher than that with linearly polarized two-color femtosecond pulses in high laser intensity. By solving time-dependent Schrödinger equation, this enhancement is well explained based on the analysis of electron tunneling ionization and subsequent dynamics.

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.

Terahertz ͑THz͒ emissions of an isolated atom in an ultrashort ͑100 fs͒ laser field are simulated by solving the time-dependent Schrödinger equation. From numerical calculations with one-and three-dimensional hydrogen atom models and a short-range shallow potential model, it can be concluded that continuum THz emissions occur more readily following transitions involving intermediate states above rather than those well below the ionization threshold of the system. Line-shaped THz emissions from transitions between high-lying Rydberg states are also found. The models are also used to describe the observed enhanced terahertz emissions with a superposed second-order harmonic laser field or a spatially constant electric field. The dependence of the THz field strength on the intensities of the fundamental laser field and the superposed field is also examined. Strong field approximation is extended to analyze the general features of THz emissions resulting from continuum free-free transitions of an electron in strong laser fields. These calculations contribute to an understanding of the THz emission processes when strong laser fields interact with atomic and molecular systems that have larger ionization potentials and where multiphoton processes are involved in order to generate THz emissions effectively.

Understanding the evolution of molecular electronic structures is the key to explore and control photochemical reactions and photobiological processes. Subjected to strong laser fields, electronic holes are formed upon ionization and evolve in the attosecond timescale. It is crucial to probe the electronic dynamics in real time with attosecond-temporal and atomic-spatial precision. Here, we present molecular attosecond interferometry that enables the in situ manipulation of holes in carbon dioxide molecules via the interferometry of the phase-locked electrons (propagating in opposite directions) of a laser-triggered rotational wave packet. The joint measurement on high-harmonic and terahertz spectroscopy (HATS) provides a unique tool for understanding electron dynamics from picoseconds to attoseconds. The optimum phases of two-color pulses for controlling the electron wave packet are precisely determined owing to the robust reference provided with the terahertz pulse generation. It is noteworthy that the contribution of HOMO-1 and HOMO-2 increases reflecting the deformation of the hole as the harmonic order increases. Our method can be applied to study hole dynamics of complex molecules and electron correlations during the strong-field process. The threefold control through molecular alignment, laser polarization, and the two-color pulse phase delay allows the precise manipulation of the transient hole paving the way for new advances in attochemistry.