Expansion of the tuning range of injection-seeded terahertz-wave parametric generator up to 5 THz

In this paper, we report the improvement of the frequency tuning range of an injection-seeded terahertz (THz)-wave parametric generator (is-TPG). A significant previous limitation was the high absorption coefficient in the higher-frequency region of a MgO:LiNbO3 crystal. Here, we inclined the crystal slightly, so that a fraction of the pump beam was internally reflected at the THz-wave exit surface of the crystal. In this configuration, it was easier for a higher-frequency THz wave to reach the crystal surface, because the center core region of the pump beam was closer to the exit surface. As a result, the upper limit of the frequency tuning range increased from 3.0 to 5.0 THz.