Tanghe Ivo, Butkus Justinas, Chen Kai, Tamming Ronnie R, Singh Shalini, Ussembayev Yera, Neyts Kristiaan, van Thourhout Dries, Hodgkiss Justin M, Geiregat Pieter
Photonics Research Group, Ghent University, Gent 9000, Belgium.
Physics and Chemistry of Nanostructures, Department of Chemistry, Ghent University, Gent 9000, Belgium.
Nano Lett. 2022 Jan 12;22(1):58-64. doi: 10.1021/acs.nanolett.1c03181. Epub 2021 Dec 29.
Two-dimensional (2D) semiconductors are primed to realize a variety of photonic devices that rely on the transient properties of photogenerated charges, yet little is known on the change of the refractive index. The associated optical phase changes can be beneficial or undesired depending on the application, but require proper quantification. Measuring optical phase modulation of dilute 2D materials is, however, not trivial with common methods. Here, we demonstrate that 2D colloidal CdSe quantum wells, a useful model system, can modulate the phase of light across a broad spectrum using a femtosecond interferometry method. Next, we develop a toolbox to calculate the time-dependent refractive index of colloidal 2D materials from widely available transient absorption experiments using a modified effective medium algorithm. Our results show that the excitonic features of 2D materials result in broadband, ultrafast, and sizable phase modulation, even extending to the near infrared because of intraband transitions.
二维（2D）半导体有望实现各种依赖光生电荷瞬态特性的光子器件，但对于折射率的变化却知之甚少。相关的光学相位变化根据应用的不同可能是有益的或不理想的，但需要进行适当的量化。然而，用常规方法测量稀释二维材料的光学相位调制并非易事。在这里，我们证明了二维胶体CdSe量子阱，一个有用的模型系统，可以使用飞秒干涉测量方法在很宽的光谱范围内调制光的相位。接下来，我们开发了一个工具箱，通过使用改进的有效介质算法，从广泛可用的瞬态吸收实验中计算胶体二维材料随时间变化的折射率。我们的结果表明，二维材料的激子特性导致宽带、超快和可观的相位调制，甚至由于带内跃迁而延伸到近红外。
