黑磷中的中红外自发与受激发射动力学
Mid-infrared spontaneous and stimulated emission dynamics in black phosphorus
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中文总结 AI 辅助
本研究开发结合波长上转换与超导单光子探测的时间分辨中红外发射显微镜，揭示黑磷在约70K时的发射类型转变及泵浦阈值以上的受激发射现象，阐明其载流子动力学并确立相关研究方法。
中文摘要 AI 辅助
黑磷（BP）因具有直接且厚度可调的带隙能量、高度各向异性的光学跃迁，以及潜在受抑制的俄歇复合，作为面向中红外（MIR）光子学的发光层状半导体受到关注。然而，由于中红外区域的时间分辨发射光谱测量颇具挑战，黑磷中由载流子复合主导的自发与受激发射动力学仍未被探究。本研究开发了一种结合波长上转换与超导单光子探测的时间分辨中红外发射显微镜，该方法可在约4.6μm波长下，以低于100皮秒的时间分辨率观测光激发黑磷的发射动力学。温度依赖测量显示，在约70K时存在从激子发射到电子-空穴等离子体发射的转变，这一结论得到了特征转变温度、泵浦通量依赖关系以及中红外发射的上升和衰减动力学的独立结果支持。在悬浮黑磷结构中，进一步观测到发射强度在明确的泵浦阈值以上呈非线性增长，且阈值以上出现光谱窄化和强皮秒发射脉冲，为法布里-珀罗腔光学反馈辅助的受激发射提供了确凿证据。这些结果阐明了黑磷中的超快载流子动力学与光学增益形成机制，并确立了时间分辨上转换光谱作为研究中红外光子学材料与器件的强大手段。
英文摘要
Black phosphorus (BP) has attracted attention as a light-emitting layered semiconductor for mid-infrared (MIR) photonics owing to its direct and thickness-tunable bandgap energy, highly anisotropic optical transitions, and potentially suppressed Auger recombination. However, spontaneous and stimulated emission dynamics governed by carrier recombination in BP have remained unexplored because time-resolved emission spectroscopy is challenging in the MIR region. Here we develop a time-resolved MIR emission microscope combining wavelength upconversion with superconducting single photon detection. This approach enables observation of emission dynamics in photoexcited BP at a wavelength around 4.6 μm with sub-100-ps temporal resolution. Temperature-dependent measurements reveal a crossover from excitonic to electron-hole plasma emission at around 70 K, supported by independent results in the characteristic transition temperature, pump-fluence dependence, and rise and decay dynamics of MIR emission. In a suspended BP structure, we further observe a nonlinear increase in the emission intensity above a well-defined pump threshold. Spectral narrowing and intense picosecond emission pulses appear above the threshold, providing solid evidence of stimulated emission assisted by optical feedback from a Fabry-Pérot cavity. These results elucidate ultrafast carrier dynamics and optical gain formation in BP and establish time-resolved upconversion spectroscopy as a powerful approach for investigating MIR photonic materials and devices.
