Tunable terahertz generation at quasi-phase matching structures using femtoscond laser pulses

We demonstrated tunable and narrow-band terahertz generation around l~3 THz via difference frequency generation (DFG) using femtosecond (fs) pulses in a periodically poled lithium niobate (PPLN) crystal and periodically poled stoichiometric lithium tantalate (PPSLT) crystal. Two different types of terahertz radiation, forward and backward, could be generated in the quasi-phase matching (QPM) structures by the DFG process. A broadband fs optical pulse contributes to the DFG process, which occurs between two different frequency components set of an ultrashort optical pulse within the frequency range and a terahertz frequency at the QPM structure. We observed a backward terahertz radiation at approximately 1.3 THz at PPLN crystal and the frequencies of terahertz radiations are easily controlled by varying the domain structures.