Fachbereich Physik and Research Center OPTIMAS, Technische Universität Kaiserslautern, Erwin-Schrödinger-Str. 46, 67663 Kaiserslautern, Germany.
Science. 2011 Sep 23;333(6050):1723-6. doi: 10.1126/science.1209206. Epub 2011 Aug 11.
We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response.
我们介绍了一种光谱方法，该方法可以确定超越光学衍射极限的非线性量子力学响应函数，并允许对纳米级相干性进行直接成像。在已建立的相干二维（2D）光谱学中，使用三个入射波和一个出射波来测量四波混频响应；因此，该方法在空间分辨率方面存在衍射极限。在相干 2D 纳米显微镜中，我们使用四个入射波，并通过光电子显微镜检测最终状态，其空间分辨率为 50 纳米。我们从波纹状银表面记录了局部纳米光谱，并观察到亚波长 2D 线形状变化。局部激发的等离子体相干相位相干性持续了大约 100 飞秒，并表现出相干拍频。通过模型可以很好地解释这些观察结果，该模型表明，耦合振荡器导致在混合暗模和亮模响应中出现类似 Fano 的共振。
