Mechanisms of Terahertz Generation under Femtosecond Pulses propagation in Nanocomposites

Terahertz (THz) generation has a high potential for study vibrational and rotational transitions, dynamics of free carriers and phonon resonances, as well as applications for lasing, security systems, spectroscopy, biomedicine, ultrafast switching and controlling of magnetic domains, molecular alignment, particle acceleration, THz-enhanced attosecond pulse generation [1] . The challenge is to produce a compact intense THz- source, for that a development of schemes and devices providing high efficiency of frequency conversion is important. For the moment, it may reach a few percent in different schemes such as optical rectification, laser-solid interaction, two-color gas-plasma scheme, laser pumped liquid-plasma [2] . Prospective media for these aims are nanocomposites (NC) due to their large nonlinearities bringing wide set of the possibilities. Large value of permanent dipole moment (PDM) is revealed (~10 2 - 10 3 Debye) in nanostructures, in particular, semiconductor quantum dots (QDs) of ZnO, ZnS, CdSe what is comparable with values of transition dipole moments between the exciton states. As well, the additional transitions between exciton states allowed due to PDM may play a significant role in the nanoparticle response, in particular for the generation of new frequencies in the THz range.