Broadband and high power terahertz pulse generation beyond excitation bandwidth limitation via chi2 cascaded processes in LiNbO3.

We proposed a novel THz generation technique beyond the limitation of the input optical pulse width, based on phase modulation via cascaded chi((2)) process. When intense THz electric field generated by optical rectification lies in electro-optic (EO) crystal, emitted THz field gives phase modulation to the optical excitation pulse. The phase modulation causes excitation pulse narrowing and consequently gives rise to the enhancement of conversion efficiency and THz wave bandwidth broadening. We experimentally realize this generation technique with high chi((2)) EO crystal LiNbO(3) and with subpicosecond pulse from Yb-doped fiber laser. It opens new concept of THz technologies.