Sub GV/CM terahertz radiation by coherent transition radition in ultrashort laser-solid interaction

We achieved broadband terahertz radiation with extreme high peak power by femtosecond laser interaction with thin solid foil via particle-in-cell simulations. The angular distribution, temporal profile and spectra of the radiation are studied and reveal that it is coherent transition radiation emitted by hot electrons which are produced in laser plasma interaction and crossing the target surfaces. The THz radiations are emitted to the broad space, strongest along the target surface and weakest in a direction between the target normal and specular reflection direction. Under laser with different peak intensities from 1017 to 1019 W/cm2, the angular distribution of the radiations does not change much. Intensity of the THz radiation is explored and shows close correlation to the target and laser parameters. Conversion efficiency of the THz radiation can be as high as a few times of 10−3. A theory model is given, as well as comparison with recent experimental observations.