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We have succeeded in developing tunable picosecond terahertz (THz)-wave parametric oscillators (ps-TPOs) by employing a noncollinear pump-enhanced signal-resonant cavity. As a parametric gain medium, we use two different shapes of unpoled, 5 mol% MgO-doped lithium niobate (MgO:LiNbO3) crystal: 1) a rectangle for Si-prism output-coupler technique and 2) a trapezoid for surface-emitted configuration. Unlike conventional nanosecond TPOs (ns-TPOs), these ps-TPOs are synchronously pumped by a mode-locked 1.5-ps Ti:sapphire laser operating at 780 nm. To overcome the high pump threshold due to the strong absorption by MgO:LiNbO3 in the THz region, we employ a pump-enhanced cavity which is carefully designed for the noncollinear dual resonance of both pump and signal waves. By slightly translating the position of one of the ps-TPO cavity mirrors, we experimentally find that the THz-wave peak frequency is continuously tunable from 0.9 to 3.3 THz, approximately, with the average output power of dozens of nanowatts. In all the above tuning range, especially above 2 THz, the THz-wave output of the surface-emitting ps-TPO using the trapezoidal MgO:LiNbO3 crystal is enhanced several times more than that of the Si-prism-coupled ps-TPO using the rectangular MgO:LiNbO 3 crystal due to the suppression of the absorption loss in MgO:LiNbO3. [ABSTRACT FROM PUBLISHER]

We reported a high-efficiency second harmonic generation (SHG) of a low-power mode-locked picosecond Ti:sapphire laser, whose average output power was less than 1 W, using a BiB3O6 (BiBO) nonlinear crystal installed in an external enhancement cavity. Ultraviolet (UV) coherent light at 389 nm with the maximum average power of 506 mW was obtained with the input average power of 805 mW using the external cavity. Considering the reflective loss of the output coupler of the 389-nm light, we could estimate the intrinsic conversion efficiency of 70%. This value, to the best of our knowledge, is the highest conversion efficiency for SHG using a BiBO crystal, even at the relatively low fundamental power. [ABSTRACT FROM AUTHOR]