Ultrafast terahertz (THz) spectroscopy is a potent tool for studying the fundamental properties of matter. Limitations of current THz sources, however, preclude the technique being applied in certain advanced configurations or in the measurement of, e.g., strongly absorbing samples. In response to this problem, here we demonstrate the generation of 1.38 mW broadband THz radiation at 10 MHz repetition rate by combining the highly efficient nonlinear organic crystal HMQ-TMS with ultrafast pump pulses generated using a simple and stable external pulse compression of a high power, near-infrared (NIR) femtosecond ytterbium-doped fiber (Yb:fiber) laser. Utilizing spectral broadening in a large core, polarization maintaining photonic crystal fiber and a pair of SF11 prisms, we achieve a tenfold pulse compression of the Yb:fiber laser, yielding compressed 0.35 µJ pulses with a full-width at half maximum pulse duration of 22 fs, exerting a peak power of 13.8 MW at a repetition rate of 10 MHz. THz generation through optical rectification of the NIR pulses is explored in two distinct thicknesses of the organic crystal, leading to a maximum conversion efficiency of ∼5.5 · 10⁻⁴, an order of magnitude higher than that achieved with inorganic nonlinear crystals, e.g., gallium phosphide, for similar pump parameters. The focused THz beam has a peak on-axis field strength greater than 6.4 kV cm⁻¹ in unpurged atmosphere. We believe that our moderately strong-field THz source is well suited to a variety of applications in ultrafast THz spectroscopy, in particular THz-enabled scattering-type near-field, and scanning tunneling spectroscopy, where multi-MHz repetition rate sources are required.

中文翻译：

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在有机晶体中以MHz重复频率产生大功率几个周期的THz

超快太赫兹（THz）光谱学是研究物质基本性质的有效工具。但是，当前太赫兹源的局限性使该技术无法应用于某些高级配置或例如强吸收样品的测量中。针对此问题，在此我们通过结合高效的非线性有机晶体HMQ-TMS和使用简单而稳定的大功率外部脉冲压缩产生的超快泵浦脉冲，演示了以10 MHz重复频率产生1.38 mW宽带THz辐射，近红外（NIR）飞秒掺y光纤（Yb：fiber）激光器。利用大芯中的光谱加宽，保偏光子晶体光纤和一对SF11棱镜，我们实现了Yb：光纤激光器的十倍脉冲压缩，µ J脉冲具有最大宽度的一半，最大脉冲持续时间为22 fs，以10 MHz的重复频率施加13.8 MW的峰值功率。在两种不同厚度的有机晶体中探索了通过近红外脉冲的光整流产生的太赫兹，导致最大转换效率约为5.5·10 ^-4，比无机非线性晶体（例如镓）的转换效率高一个数量级。磷，用于类似的泵参数。聚焦的太赫兹光束的峰值场强大于6.4 kV cm ^-1在纯净的气氛中。我们相信我们中等强度的太赫兹源非常适合超快太赫兹光谱的各种应用，特别是需要太赫兹重复频率源的太赫兹散射型近场和扫描隧道光谱。