有机半导体/金属杂化纳米结构中的强耦合相互作用及超快动力学特性

Strong coupling and ultrafast dynamics in organic semiconductor/metal hybrid nanostructures

有源表面等离光子学(active plasmonics)是目前表面等离子体光子学研究的一个重要分支,其基本思想是利用―增益‖物质和纳米金属结构相结合形成杂化金属纳米结构,从而克服表面等离子体激元(surface plasmon polariton,SPP)的耗散问题以及实现对SPP光子的外部操作和调制。本文主要针对有机半导体/金属杂化纳米结构,介绍其相关研究结果。结合色散补偿的光谱相干法和超快泵浦-探测瞬态光谱测量技术,分析了J-凝聚/光栅杂化金属纳米结构的静态和瞬态光学特性,揭示了X-SPP的强耦合过程中的相干和非相干相互作用通道,杂化能态的sub/super-radiance现象,以及有机半导体染料中的激子和SPP之间的瞬态相干能量交换过程:―拉比‖振荡。实现了10 fs量级的SPP光学特性的外部相干调制。

Active plasmonics, as an important branch of Plasmonics, is growing rapidly over the last decades. The main principle of active plasmonics is to combine surface plasmon polaritons （SPPs） with ＇active＇ materials to compenstate intrinsic weak optical nonlinearities and short propagation lengths of SPPs, so that external manipula- tion and coherent control of SPPs can be realized. Here, we give a brief review of the studies in the area of active plasmonics. In particular, we focus on hybrid J-aggregate/metal nanostructures consisting of J-aggregate excitons and surface p/asmon polaritons supported by metattic nanostructures. Two experimental methods： chrfp-compen- sated spectral interferometry and nonlinear pump-probe spectroscopy are introduced. The strong coupling between J-aggregate excitons and SPPs is studied in detail by probing both the static optical properties and ultrasfast dy- namics of the strongly coupled X-SPP systems. The results reveal that two different energy transfer channels： a coherent resonant dipole-dipole interaction and an incoherent exchange of photons, are coexisting in the hybrid system. Coherent energy exchange, that is, Rabi oscillations between the excitonic and the SPP systems in real time are also investigated. It is found that coherent X-SPP population transfer induces transient oscillations in exciton density, leading to a periodic modulation of the normal mode splitting and thus optical nonlinearity on a 10 fs time- scale.