Sun Jia-Zhong

Harmonic Enhancement Mechanism of a Superposition State Atom Irradiated by Short Pulses

We investigate the high-order harmonic generation (HHG) of a model atom whose initial state is prepared in a superposition of its ground state and an excited state irradiated by different duration laser pulses. Compared to the HHG generated from an atom whose initial state is in its ground state, its conversion efficiency obtains some enhancement. The enhancement originates from the higher ionization rate (rather than the ionization yield) of the atom with superposition initial state.

Ultrahigh Harmonic Generation from an Atom with Superposition of Ground State and Highly Excited States

We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.

Electronic structure and crystalline electric field in RCo5 (R = Y, La, Ce, Pr, Nd, Sm, Gd, and Tb)

Self consistent charge and spin-polarized local spin density approximation functional theory calculations based on the discrete variational method have been performed for RCo5 (R = Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) compounds. The partial density of states of the Pr atom in the PrCo6Co12 cluster is established to be strikingly similar to that of the Ce atom in the CeCo6Co12 cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii r4f and r4f2 of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthanide contraction. The crystalline electric field (CEF) parameter A20 at the R site is calculated using a real charge distribution ρ(R) in the cluster, except for Pr and Nd, and is in agreement with that evaluated based on the single-ion model. This result shows that the CEF parameter A20 is mainly determined by the near electronic structure. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitals in some single-electron-molecular-orbitals, which are near the Fermi energy level and occupied by electrons. For light rare-earths the R-4f electrons in RCo6Co12 (R = Y, La, Ce, Pr, Nd, and Sm) clusters are not localized entirely and a small amount of the R-4f electrons have itinerant properties.