In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.
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机译：在这项研究中，我们对块状Ge进行了800-nm抽运和超高分辨力（70（fs）的超宽带中红外（MIR）探针光谱分析。通过将时间分辨差反射光谱[ΔR（ω）/ R（ω）]与Drude模型拟合在200–5000 cm -1 区域中，可以得到随时间变化的等离子体频率和散射率已经获得。通过计算，我们可以进一步得到与时间有关的光激发载流子浓度和载流子迁移率。俄歇复合基本上控制了100 ps内光激发载流子的快速弛豫，然后由于扩散而缓慢弛豫。另外，在2000 cm −1 附近的时间分辨差反射光谱中，特别是对于高泵浦注量，它清楚地发现了一种新的振荡特征，由于库仑力的作用，洛伦兹振荡持续约20 ps。兴奋之后。
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