We report on efficient THz generation in DAST by optical rectification of intense mid-IR pulses centered at (i) 3.9 μm and (ii) its second harmonic at 1.95 μm. Suppression of multi-photon absorption shifts the onset of saturation of the THz conversion efficiency to pump energy densities, which are almost an order of magnitude higher as compared to conventional pump schemes at 1.5 μm. Despite strong linear absorption at 3.9 μm, DAST exhibits a high optical-to-THz conversion efficiency, which we attribute to resonantly enhanced nonlinearity and advantageous phase matching of the THz phase velocity and group velocity of the driving pulse. At 1.95 μm, we find that low linear and multi-photon absorption in combination with cascaded optical rectification lead to record optical-to-THz conversion efficiencies approaching 6%. The observed high sensitivity of the THz generation to the parameters of the mid-IR driving pulses motivates an in-depth study of the underlying interplay of nonlinear wavelength- and intensity-dependent effects.

中文翻译：

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通过对DAST中的IR脉冲进行光整流来高效生成THz

通过强烈的中红外脉冲光整流我们高效的THz产生在DAST报告居中位于（i）3.9  μ m和（ii）该二次谐波在1.95  μ米。多光子吸收的抑制转移的太赫兹转换效率饱和的开始到泵的能量密度，这是几乎一个更高比在1.5传统的泵方案量级 μ米。尽管在3.9强线性吸收 μ米，DAST表现出高的光到太赫兹的转换效率，这是我们归因于共振增强非线性和太赫兹相速度的有利相位匹配和驱动脉冲的群速度。在1.95  μm，我们发现低线性和多光子吸收与级联的光整流相结合，导致记录的光到太赫兹转换效率接近6％。观察到的THz产生对中红外驱动脉冲参数的高度敏感性，促使人们深入研究非线性波长和强度相关效应的潜在相互作用。