Design, fabrication and test of a cascaded plamonic superlens

在常规显微镜下直接观察的超分辨率成像对于生物和纳米技术来说是非常可取的，因为它能够对纳米尺寸的物体进行无损成像和监测。为了实现可见光波长下的远场实时超分辨成像，本课题研究了一个由两个等离子激元组成的级联等离子体超透镜系统。一种是双层弯曲腔(DLMC)结构，用于支持具有大空间频率的波的传播。另一种是平面等离子体透镜(PPL)，用于将来自DLMC结构的波以放大方式耦合到自由空间。在本项目的第一阶段，我们对级联等离子体超透镜系统进行了数值研究和制作。我们的模拟结果表明，在640 nm波长下，成像系统具有预期的亚波长成像能力。还成功地制作了两个独立的等离子体元件，实现了对结构参数的精确控制。然而，目前的设计仍有一些局限性。在二期工程中，我们将通过结构修改和优化来解决这些问题。我们将进一步优化系统的几何参数，以减小DLMC和PPL之间的耦合距离，从而促进两者在纳米制造中的集成。我们还将优化DLMC结构的纳米制造工艺，以增加其光透过率。通过修改DLMC结构的中心区域，解决了现有级联成像系统中物体与弯曲沟槽之间的对准问题。最后，利用我们的航空图像扫描显微镜制作了经过改进设计的优化成像系统，并对所制作的超透镜背后的场分布进行了表征。

Super-resolution imaging with direct observation under conventional microscopes is highly desirable for biological and nano-technologies since it is capable of non-destructive imaging and monitoring for nano-sized objects. To achieve far field real-time super-resolution imaging at visible wavelength we study a cascaded plasmonic superlens system in this project, which is composed of two plasmonic elements. One is a double layer meander cavity (DLMC) structure used to support the propagation of waves with large spatial frequencies. The other one is a planar plasmonic lens (PPL) used to couple the waves from the DLMC structure to free space with magnification. In the first phase of this project we have numerically studied and fabricated the cascaded plasmonic superlens system. Our simulation demonstrated the expected subwavelength imaging capability with magnification of the imaging system at 640 nm wavelength. The two individual plasmonic elements were also fabricated successfully, with which precise control of structural parameters was demonstrated. However, there are still some limitations with the current design. In the second phase of the project we will solve these problems through structure modification and optimization. We will further optimize geometrical parameters of the system in order to reduce the coupling distance between the DLMC and the PPL, which will facilitate the integration of the two elements in nano-fabrication. We will also optimize the nano-fabrication process of the DLMC structure to increase its optical transmission. Through modifying the center area of the DLMC structure, we will solve the alignment problem between the object and the meander grooves with the current cascaded imaging system. Finally, the optimized imaging system with modified design will be fabricated and field distributions behind the fabricated superlens will be characterized by using our aerial image scanning microscope