Terahertz Radiation From Metal Surfaces, Cu₂O/Metal Interfaces And Silicon Surfaces

So far, high efficient terahertz emitter is still the key point and the bottle-neck of terahertz research and application. This thesis mainly studied terahertz radiation from metal surfaces, Cu₂O/Metal interfaces and silicon surfaces. Through different experimental manners, we discussed the possible mechanisms of terahertz radiation from these surfaces.In our experiment, a special mechanical framework was used to study terahertz radiation from metal surfaces. In comparison with pre-works, we conclude that when the energy of single laser pulse is small and surface plasmons aren't excited, terahertz radiation can't be generated from metal surfaces.During the study of terahertz radiation from metal surfaces, we accidently found relatively stronger terahertz radiated from Cu₂O/Metal interfaces. Then we fabricated a film of Cu₂O/Au. And terahertz field from this film is about a tenth of that from InAs. If we can optimize the parameters of this film, it's possible that a film that radiates stronger terahertz could be made.Terahertz radiation from silicon surface is very weak. In our experiment, terahertz field from silicon surfaces is about 1/500 of that from InAs surfaces. Measuring the azimuthal dependence of terahertz field from silicon surface, we observed a fourfold azimuthal dependence. Several years ago, researchers have found this azimuthal dependence of SHG from silicon surface, which is the same as what we observed. Therefore, the physical mechanisms of the azimuthal dependence of terahertz from silicon surfaces should be similar to that of SHG. That‘s to say, they both stem from the electric quadrupole-magnetic dipole. Then we also found that terahertz intensity from roughed silicon was about 25 times stronger than that from polished silicon. And the terahertz intensity was strongly dependent on the roughed direction.