摘要
In the far-infrared spectrum between 20 and 60 µm, the free-electron laser (FEL) is the only wavelength-tunable coherent radiation source capable of generating kilowatt to megawatt peak powers with a linewidth of the order of 1%. Here, we report the detection of >70 kW radiation power at about 52 µm in a <94 ps pulse width from a KTiOPO <sub>4</sub> (KTP) off-axis terahertz (THz) parametric oscillator at room temperature, when pumping it with 11.9 mJ energy in a 450 ps pulse from a single-frequency Nd:YAG laser and seeding it with a 14 µJ, 40-GHz-linewidth Stokes pulse from a synchronously pumped KTP parametric generator. When limiting the radiation to a linewidth of ~8 × 10 <sup>-4</sup> , we measured >45 kW radiation power for the far-infrared radiation. With 63% coupling efficiency of the silicon prism atop the KTP crystal, the measured >70 and >45 kW far-infrared radiation correspond to >111 and >71 kW powers extracted from the KTP crystal of the seeded off-axis THz parametric oscillator. The radiation source accomplished in this work has great potential to become a tabletop and economical alternative for the bulky and expensive far-infrared FELs in national facilities.