We employ energy-momentum spectroscopy on isolated organic single crystals with micrometer-sized dimensions. The single crystals are grown from a thiophene-based oligomer and are excellent low-loss active waveguides that support multiple guided modes. Excitation of the crystals with a diffraction-limited laser spot results in emission into guided modes as well as into quasi-discrete radiation modes. These radiation modes are mapped in energy-momentum space and give rise to dispersive interference patterns. On the basis of the known geometry of the crystals, especially the height, the characteristics of the interference maxima allow one to determine the energy dependence of two components of the anisotropic complex refractive index. Moreover, the method is suited to identify the orientation of molecules within (and around) a crystalline structure.

中文翻译：

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能量动量光谱法可视化有机单晶中激子发射的自干扰

我们对具有微米级尺寸的分离的有机单晶采用能量动量光谱。单晶由噻吩基低聚物生长而成，并且是出色的低损耗有源波导，可支持多种导模。用衍射极限激光点激发晶体会导致发射成导模以及准离散辐射模。这些辐射模式映射在能量动量空间中，并产生色散干涉图。根据晶体的已知几何形状，尤其是高度，干涉最大值的特性使人们能够确定各向异性复折射率的两个分量的能量依赖性。而且，该方法适合于识别晶体结构内（和周围）的分子的取向。