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Parametric generation of terahertz wave pumped by picosecond Ti:sapphire laser with MgO-doped LiNbO3 installed in external enhancement cavity

We developed parametric generation of terahertz (THz) wave based on noncollinear phase-matching condition in 5 mol% MgO-doped LiNbO3 (MgO:LN) crystal synchronously pumped by a low-power mode-locked picosecond Ti:sapphire laser whose average output power was less than 1 W in simple external enhancement cavity. Considering the idler (Stokes) light made an angle of approximately 1 degree with the pump light corresponding to the noncollinear phase-matching condition, we built the extremely-simple doubly-resonant cavity, which composed of only four mirrors, in which the idler light was resonated as well as the pump light simultaneously without any feedback systems for the idler light to reduce the pumping threshold of the THz wave parametric process. As a result, we obtained a broad output THz wave at around 0.9 THz confirmed by Michelson interferometer and achieved the pumping threshold of peak intensity of 50 MW/cm2. This threshold is, to the best of our knowledge, the lowest value of externally pumped THz wave parametric oscillation.