Probing polariton condensation dynamics by multiquantum coherent spectroscopy in organic optical microcavities

“塑料”激光器的前景令人兴奋，因为每个组件都由聚合物或分子组成，因为这些可以简单地从溶液中加工，大大降低了制造成本，而且因为塑料的灵活性为构思柔性激光器提供了机会。此外，每个元件的光学特性可以综合调谐；这些材料可以设计成在可见光谱的红色、绿色或蓝色区域非常有效地发光。然而，实现商业上可行的塑料激光器面临许多挑战，主要是因为这些材料的激发态强烈吸收波长接近发射波长的光，因此高激发态密度是诱导激光效应所必需的。然而，一种有希望的替代方法已经被提出并证明使用传统的半导体，即所谓的极化激光器。这些装置利用光与电子的强相互作用，产生了新的准粒子，这些准粒子可以被认为是部分光子和部分电子。这些准粒子被称为极化子，它们具有非常特殊的性质，即所谓的玻色子。实际上，这意味着两个或两个以上的极性可能占据相同的量子力学状态。如果玻色子密度足够高，其中很大一部分占据最低量子态，此时量子效应（相干性；就像一群合作的溜冰者在聚光灯下表演精美的舞蹈）在宏观尺度上自发地变得明显，即极化子波函数在大的长度尺度上空间重叠。极化子的强光子特性使得这种相干性在一定程度上对激子（受激电子）来说是一个挑战，激子是“脏”玻色子，在高密度下经历相互湮灭。在极化激子激光器中，自发相干是激光的起源，脱离自发相干态的光泄漏是激光的来源。在这个项目中，我们将开发一个实验装置，以前所未有的细节探测产生自发相干的极化之间的相互作用。

The prospect of 'plastic' lasers, in which each component is composed of polymers or molecules, is exciting because these can be processed simply from solution, reducing significantly their cost of fabrication, and because the flexibility of plastics presents opportunities to conceive flexible lasers. Furthermore, the optical properties of each component can be tuned synthetically; these materials can be designed to emit light very efficiently in the red, green or blue regions of the visible spectrum. However, implementing commercially viable plastic lasers presents many challenges, primarily because excited states of these materials absorb light strongly at wavelengths close to the emission wavelength, and thus high excited-state densities are necessary to induce laser effects. However, a promising alternative approach has been proposed and demonstrated using traditional semiconductors, so-called polariton lasers. These devices exploit the strong interaction of light and electrons, in which new quasi-particles that can be considered to be part photons and part electrons, are generated. These quasi-particles are termed polaritons, and they have the very special property that are so-called bosons. Practically, this means that two or more polaritons may occupy the same quantum-mechanical state. If the boson density is high enough, a large fraction of these occupy the lowest quantum state, at which point quantum effects (coherence; like a large ensemble of cooperative skater pairs all performing in exquisite choreography when the spotlight is upon them) become apparent spontaneously on a macroscopic scale, i.e., the polariton wavefunctions overlap spatially over large lengthscales. The strong photonic character of polaritons permits such coherence to an extent that is challenging for excitons (excited electrons), which are 'dirty' bosons and undergo mutual annihilation at high density. Spontaneous coherence is at the origin lasing in polariton lasers: the optical leakage of out of the spontaneously coherence state is the source of laser light. In this project, we will develop an experimental apparatus that will probe with unprecedented detail the interactions between polaritons that give rise to spontaneous coherence.