Rydberg Exciton Interaction Dynamics

里德堡激子是相当于里德堡原子的固态激子，它们有许多令人着迷的性质，例如相互之间的巨大相互作用，直到里德堡阻塞点。它们也可以用来作为探测自由载流子存在的敏感探针，这种自由载流子会产生类似的封锁效应，称为等离子体封锁，其密度已经低于每立方微米0.01个电子-空穴对。对于旨在利用里德堡封锁的后续试验，能够区分这两种封锁机制并确定它们是至关重要的。与里德堡原子相比，半导体环境导致了更快、更复杂的载流子和布居动力学，这需要首先详细了解。例如，预计自由载流子可能很快形成束缚激子态，而激子可能通过与声子的相互作用而电离，所以在很长一段时间内，通常情况下这两种阻塞机制都是可能的。因此，本项目的主要目的在于通过时间分辨和空间分辨光谱来更深入地了解复杂的布居动力学。为此，该项目旨在借助一种定制的调制器来研究时间分辨里德堡阻塞，该调制器可以产生持续时间约为500 ps到1 ns的傅立叶受限脉冲。这将使我们能够进行泵浦-探测实验，这将有助于揭示等离子体中激子的形成速度、里德堡激子的电离率、它们向低能态的松弛以及副激子在俄歇辅助下形成等离子体的过程。此外，我们将重点研究传输效应和阻挡效率的空间分辨测量，以更深入地了解里德堡激子之间相互作用势的空间相关性，并了解不同主量子数极化子的传播速度引起的色散效应是否会导致相互作用在晶体内部的不同位置或不同时间发生变化。最后，我们还将研究偶极禁能激子对其光学活性激子的影响。这里，我们将集中讨论S激子和D激子，它们的波函数与P激子的波函数有很大的不同，这意味着相互作用势可能相当复杂。在这里，我们将进行双光子吸收和二次谐波光谱，以故意激发由于改变了双光子吸收的选择规则而产生的偶极禁戒态。总之，本项目的主要目的在于详细了解Cu2O中几个激子态和自由载流子态的布居动力学及其相互作用。

Rydberg excitons are the solid state equivalent to Rydberg atoms and share many of their fascinating properties, for example huge interactions among each other up to the point of Rydberg blockade. They may also be used as sensitive probes for the presence of freecarriers, which cause similar blockade effects termed Plasma blockade already at densities of less than 0.01 electron-hole-pairs per cubic micrometer. For subsequent experiments aimed at harnessing Rydberg blockade, it is of fundamental importance to be able todistinguish between these two blockade mechanisms and to create them deterministically. In comparison to Rydberg atoms, the semiconductor surrounding causes faster and more complex carrier and population dynamics which need to be understood in detail first.For example, it is expected that free carriers may form bound exciton states quickly, while excitons may be ionized e.g. by interaction with phonons, so for long times, in general a mixture of both Blockade mechanisms is expected. Therefore, the main aim of the presentprojct lies in gaining a deeper understanding of the complex population dynamics via time-resolved and spatially resolved spectroscopy. To this end, this project aims at investigating timeresolved Rydberg blockade with the help of a tailored modulator that creates Fourier-limited pulses with a duration of approximately 500 PS to 1 ns. This will allow us to perform pump-probe experiments, which will shed light on the rate of exciton formation from plasma, theionization rate of Rydberg excitons, their relaxation towards lowerenergy states and the Auger-assisted formation of plasma from paraexcitons. Further, we will focus on propagation effects and spatially resolved measurements of blockade efficiency to gain a deeper understanding of the spatial dependence of the interaction potential between Rydberg excitons and to understand whether dispersion effects resulting from varying propagation velocities ofpolaritons with different principal quantum numbers result in interactions that vary at different positions inside the crystal or at different times. Finally, we will also investigate the influence of dipoleforbidden excitons on their optically active counterparts. Here, we willfocus on S- and D-excitons, which have wavefunctions with a shape that differs significantly from that of P-excitons, which implies that the interaction potential may be rather complicated. Here we will perform two-photon absorption and second-harmonic spectroscopy todeliberately excite the dipole-forbidden states due to the altered selection rules for two-photon absorption. In summary, the main aim of the present project lies in gaining a detailed understanding of the population dynamics of the several exciton and free-carrier states inCu2O and their interactions.