Terahertz radiation pattern of argon cluster irradiated with intense femtosecond laser pulses

We have investigated the angular distribution of the terahertz radiation from the argon cluster targets irradiated with the intense femtosecond laser pulses in order to study the radiation mechanism from laser produced plasmas. The relatively strong radiation was observed in the directions at 45 and 135 degrees. In those directions, the horizontally polarized radiation was much stronger than the vertical component. In order to interpret the experimental results of the angular distribution and laser polarization dependence of the radiated THz wave qualitatively, a mechanism based on the radiation from time-varying quadrupoles produced by the ponderomotive force is proposed.