Dipole THz radiation from a single cluster irradiated by high intensity and short pulse laser*

THz radiation from laser produced plasmas has been studied as an application for strong energy and compact radiation sources. Among them, high intensity THz radiation had been experimentally observed from cluster media. However, the detailed mechanism of THz radiation from the cluster has not yet been clarified theoretically. Thus, it is difficult to optimize the THz radiation by changing the laser intensity and the size of the cluster.

From the results of PIC simulation, we found that THz radiation results from the electron oscillation around a cluster driven by the laser ponderomotive force which pushes the electrons to the laser direction. After the laser irradiation, electrons oscillate by the electrostatic force from the cluster core and radiate the dipole electromagnetic field. The oscillation frequency, which corresponds to the radiation frequency, decreases to THz regime due to the decrease of the cluster density with the Coulomb expansion. We found that high emission is realized when the cluster density is kept above the cutoff density during the laser-plasma interaction. These results indicate the key process for describing the THz radiation from multi-body cluster media in the experimental system.