Digital Holographic Microscope

利用数字全息显微镜（DHM），微纳米结构可以在4D，即时间和空间分辨率表征。该方法基于相位干涉图像的记录，该图像是通过将参考激光束与来自同一源的光束叠加在一起穿透样品而产生的。与其他显微镜方法相比，DHM的特点是它不是记录物体的投影图像，而是可以重建物体图像的数字全息图。这种方法既可以对纳米分辨率的复杂结构进行精确成像，也可以对频率高达MHz范围的振动等动态过程进行分析。这种显微镜可以在反射和透射配置下操作，能够检查从MEMS/NEMS系统到生物细胞结构的各种不同样品。本提案中DHM将用于的主要研究领域包括集成在新的共谐振传感器概念中的微悬臂和纳米悬臂的表征，应用于引力透镜和光子晶体的动态光机械系统，以及传感器环境中智能聚合物的动态表面变化。所有这些应用的共同点是，它们具有复杂的三维表面形貌，可以达到纳米尺度，并且需要分析它们的静态（例如地形，变形），特别是它们的动态行为（例如振动）。由于要研究的结构和系统的尺寸较小，在后一种情况下需要低至兆赫/微秒范围的频率和时间分辨率。对于悬臂式传感器，特别是非常大的振动幅值，可以很容易地超过梁的厚度的几倍，是研究能量分布和非线性效应的兴趣。在智能聚合物的情况下，一个主要的挑战是它们通常非常柔软的表面，这极大地限制了扫描探针显微镜等接触方法的使用。数字全息显微镜是一种非接触的方法，可以满足所有这些要求，因此是进行所述主题研究的关键工具。

With digital holographic microscopy (DHM), micro- and nanostructures can be characterized in 4D, i.e. time- and space-resolved. The method is based on the recording of phase interference images, which are generated by superimposing a reference laser beam with a beam from the same source penetrating the sample. In contrast to other microscopy methods, DHM is characterized by the fact that it is not the projected image of the object that is recorded, but a digital hologram from which an object image can be reconstructed. This approach allows both a precise imaging of complex structures with nanometer resolution and the analysis of dynamic processes such as vibrations with frequencies up to the MHz range. Such microscopes can be operated in reflection and transmission configurations and enable the examination of a wide range of different samples from MEMS/NEMS systems to biological cell structures. The main areas of research for which the DHM in this proposal will be used include the characterization of micro- and nano-cantilevers, which are integrated in a new co-resonant sensor concept, dynamic optomechanical systems with applications as gravitational lenses and photonic crystals, as well as dynamic surface changes of smart polymers in a sensor context. The common denominator for all of these applications is that they feature complex three-dimensional surface topographies down to the nanometer scale and require an analysis of their static (e.g. topography, deformations) and in particular their dynamic behavior (e.g. vibrations). Due to the small dimensions of the structures and systems to be investigated, frequency and time resolutions down to the megahertz / microsecond range are required in the latter case. In the case of cantilever sensors in particular very large vibration amplitudes, which can easily exceed several times the beam’s thickness, are of interest for studying energy distributions and non-linear effects. In the case of smart polymers, a major challenge are their usually very soft surfaces which significantly limits the use of contact methods such as scanning probe microscopy. Digital holographic microscopy is a non-contact method that can meet all of these requirements and is therefore a crucial tool in conducting research in the described topics.