Detailed study of zigzag metal gratings

光子学最近有许多令人兴奋的进展，表明金属结构可以在亚波长尺度上形成图案，以表现出自然界中没有的新颖电磁特性。虽然术语超材料最近才被创造出来描述这些结构，但超材料最著名的例子可能是简单的衍射光栅。它在世纪后期首次被研究，在19世纪早期发现用于光谱学，由于刻划引擎的发展，随后大规模生产反射光栅。从那时起，这种基本设备已广泛应用于整个电磁频谱。近年来，人们对亚波长尺度上的金属透射光栅的研究引起了广泛的关注，这种新的兴趣主要是由于观察到了与波导和表面等离子体共振的激发相关的增强透射现象。这里提出的锯齿形结构提出了一种全新的，但尚未完全被忽视的超材料类型，对它的研究将汇集一些高度热门和活跃的研究领域。我们提出了一个程序的计算机建模，制造和实验表征在可见光和毫米波长非常适合两个博士生。第一个子计划将使用锯齿形光栅提供一种机制，使可见光辐射耦合到存在于银和金薄膜上的表面模式（表面等离子体）。然而，在微波频率下，金属几乎是完美的导体，不存在束缚表面波。因此，我们必须依赖于表面本身的扰动，以诱导必要的边界条件，使局部表面模式可以支持。耦合到传统的表面等离子体激元和微波等效物，将允许探索模式的传播和分散的表面上的新的对称性，以前没有考虑，包括那些手性。因此，我们期望观察到一个有趣的偏振响应，与表面能够耦合到表面模式的横向磁和横向电辐射，并可能从闪耀光栅强烈的偏振转换。我们已经对电磁辐射与这种结构的相互作用进行了理论处理，因此，该项目的一个重要部分将是将这一理论发展成计算机代码。这不仅可以与实验数据进行比较，而且还可以通过快速建模与这些令人兴奋的结构相关的整个参数空间来发现最有趣的现象。我们还将利用商业数值建模软件，虽然速度要慢得多，但这将使研究人员能够从一开始就优化和研究结构。

There have been many recent and exciting advances in photonics demonstrating that metallic structures can be patterned on the subwavelength scale to exhibit novel electromagnetic properties not found naturally. While the term metamaterial has only recently been coined to describe these structures, perhaps the most famous example of a metamaterial is the simple diffraction grating. It was first studied in the late 18th century, finding use in spectroscopy in the early part of the nineteenth century, with mass production of reflection gratings following due to the development of ruling engines. Since then, this fundamental device has been employed extensively across the whole electromagnetic spectrum. In recent years considerable attention has been focused upon the study of metal transmission gratings structured on the subwavelength scale, this renewed interest largely being due to the observation of enhanced transmission phenomena associated with the excitation of waveguide and surface plasmon resonances. The zigzag structures proposed here present an entirely new, and as yet completely overlooked type of metamaterial, the study of which will draw together a number of highly topical and active research areas. We propose a programme of computer modelling, fabrication and experimental characterisation at both visible and millimeter wavelengths ideally suited to two PhD students. The first subproject will use zigzag gratings to provide a mechanism for visible radiation to couple to the surface modes (surface plasmons) that exist on silver and gold films. However, at microwave frequencies, where metals are almost perfect conductors, no bound surface waves exist. Therefore we must rely on the perturbation of the surface itself to induce the necessary boundary conditions so that localised surface modes can be supported at all. Coupling to both traditional surface plasmons, and the microwave equivalent, will allow for an exploration of the modes' propagation and dispersion on surfaces with novel symmetries not previously considered, including those with chiral properties. We therefore expect to observe an interesting polarisation response, with the surface able to couple both transverse magnetic and transverse electric radiation into surface modes, and potentially strong polarisation conversion from blazed gratings. We have already produced a theoretical treatment for the interaction of electromagnetic radiation with such a structure, and a vital part of the project will therefore be to develop this theory into a computer code. This will not only allow for a comparison to the experimental data, but also an opportunity to discover the most interesting phenomena by quickly modelling the whole of parameter space associated with these exciting structures. We will also utilise commercial numerical modelling software, which while much slower, will enable the researchers to optimise and study the structures from the outset.