Undoubtedly, Raman spectroscopy is one of the most elaborate spectroscopy tools in materials science, chemistry, medicine and optics. However, when it comes to the analysis of nanostructured specimens or individual sub-wavelength-sized systems, the access to Raman spectra resulting from different excitation schemes is usually very limited. For instance, the excitation with an electric field component oriented perpendicularly to the substrate plane is a difficult task. Conventionally, this can only be achieved by mechanically tilting the sample or by sophisticated sample preparation. Here, we propose a novel experimental method based on the utilization of polarization tailored light for Raman spectroscopy of individual nanostructures. As a proof of principle, we create three-dimensional electromagnetic field distributions at the nanoscale using tightly focused cylindrical vector beams impinging normally onto the specimen, hence keeping the traditional beam-path of commercial Raman systems. In order to demonstrate the convenience of this excitation scheme, we use a sub-wavelength diameter gallium-nitride nanostructure as a test platform and show experimentally that its Raman spectra depend sensitively on its location relative to the focal vector field. The observed Raman spectra can be attributed to the interaction with transverse and pure longitudinal electric field components. This novel technique may pave the way towards a characterization of Raman active nanosystems, granting direct access to growth-related parameters such as strain or defects in the material by using the full information of all Raman modes.

中文翻译：

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迈向基于极化的激发剪裁，以扩展拉曼光谱

毫无疑问，拉曼光谱学是材料科学，化学，医学和光学领域最复杂的光谱学工具之一。但是，在分析纳米结构样本或单个亚波长大小的系统时，通常由于获得不同的激发方案而无法获得拉曼光谱。例如，利用垂直于衬底平面定向的电场分量进行激励是一项艰巨的任务。通常，这只能通过机械倾斜样品或通过复杂的样品制备来实现。在这里，我们提出了一种新的实验方法，该方法基于偏振定制光的利用，用于单个纳米结构的拉曼光谱。作为原理证明，我们使用通常聚焦在样本上的紧密聚焦的圆柱矢量束在纳米尺度上创建三维电磁场分布，因此保留了商业拉曼系统的传统束路径。为了证明该激发方案的便利性，我们使用亚波长直径的氮化镓纳米结构作为测试平台，并通过实验证明其拉曼光谱敏感地取决于其相对于聚焦矢量场的位置。观察到的拉曼光谱可归因于与横向和纯纵向电场分量的相互作用。这项新颖的技术可能为拉曼活性纳米系统的表征铺平道路，