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We propose an IR-pump-XUV-probe scheme to investigate multi-electron-hole coherence. Using the laser-induced ionization as a gate for XUV excitation of core electrons, it provides us the opportunity to probe both the core and valence electron dynamics.

The experimental results of SrTiO3 from 0.3THz to 6THz shows that an analytic continuation of the complex reflection can reduce the impact of limited spectra so that a more accurate correction can be acquired.

We experimentally demonstrate that the optical-to-THz conversion efficiency in circularly-polarized two-color laser fields is higher than that in linearly-polarized two-color system.

Quantum dynamics are theoretically pivotal and challenging for the non-equilibrium processes in warm dense matter. Here, the electron-ion relaxation in warm dense hydrogen is investigated by molecular dynamics (MD) simulation with Electron Force Field method (eFF). Quantum collisions are therefore included since the electrons are treated as Gaussian wave packets, and the Coulomb Catastrophe in classical MD can be avoided. The results of eFF show that the temperature relaxation time can be up to 4.1 times longer than that from current popular models and classical MD. The analyses of particle distributions, kinetic and potential energies, mean free path show that quantum degeneracy, delocalization, and cross sections of electrons with coupled ions are the intrinsic physics for the extremely low energy exchange rates in large-angle collisions and quantum electrons dominated warm dense matter.

Terahertz (THz) emission of crystal ZnO in a strong laser field and its second harmonics are simulated by solving the semiconductor Bloch equations (SBEs), which describes the coupled interband and intraband dynamics in two-band model. Due to the two-color laser field breaks the dynamic symmetry of the electronic wave packed, the THz yield is highly enhanced. The calculations show that the THz emission in solid is contributed by the directional current, which is named intraband mechanism. It can be seen that the even-harmonics oscillate two times, while THz shows a two-time oscillation in one fundamental cycle, and the optimal phase delay of THz pulse is 0.5 π. Also the dependence of THz amplitude on the amplitude of the fundamental beam is quite different from the atomic transient plasma current PC model. The dependence shows different region due to the different dynamics in solid structure. It is meaningful to investigate the channel closing during the Landau-Zener tunneling and the degree of asymmetric of the intraband current.

In this work, two kinds of THz absorption are identified from the polar molecule-formed plasma, namely, the broad band resonant absorption induced by the separation of electrons and ions within plasma, and the rotational transitions between different rotational states. Interestingly, we observe the enhanced THz absorption of the rotational transition lines within the resonant absorption frequency range. Gas pressure is varied to show that the enhanced THz absorption lines are related to the plasma frequencies. This work is not only a new observation on the THz absorption within plasma, but also a glimpse of the coherent nature of laser-prepared plasma.

Recent study on high harmonic generation(HHG) from oriented CO have shown the generation of pure even harmonics because of the permanent dipole moment in linearly polarized laser fields. In order to make it sure if permanent dipole moment results in the generation, we investigate the HHG of nonpolar molecular N2 in two-color field using time-dependent Hartree-Fock theory. The molecular axis is directed along the z axis. If linear laser fields are polarized along the y axis, there is no harmonic generation from z-axis direction. However, adding a static field (or THz) to the z axis, pure even harmonics are generated from the z-axis direction miraculously (shown in Fig.1). the results reveal the permanent dipole moment indeed results in the generation of pure even harmonics. From this, a deeply research about the influence of permanent dipole moment on HHG is necessary and it may enlighten us to generate shorter attosecond pulse in the future.

We study the ionic excitation of helium system in strong laser fields. The simulation results show that the interplay of the electron-electron correlation, singly and doubly ionization and rescattering dynamics.

We experimentally studied the dissociative double ionization of Ar2 in femtosecond laser fields of different light intensity. The experimental results show a significant regulatory effect of light intensity to dissociative double ionization of Ar2.