Gérardin Benoît, Laurent Jérôme, Legrand François, Prada Claire, Aubry Alexandre
ESPCI Paris, PSL Research University, CNRS, Univ Paris Diderot, Sorbonne Paris Cité, Institut Langevin, UMR 7587, 1 rue Jussieu, F-75005, Paris, France.
Sci Rep. 2019 Feb 14;9(1):2135. doi: 10.1038/s41598-019-38480-3.
The propagation of waves in complex media can be harnessed either by taming the incident wave-field impinging on the medium or by forcing waves along desired paths through its careful design. These two alternative strategies have given rise to fascinating concepts such as time reversal or negative refraction. Here, we show how these two processes are intimately linked through the negative reflection phenomenon. A negative reflecting mirror converts a wave of positive phase velocity into its negative counterpart and vice versa. In this article, we experimentally demonstrate this phenomenon with elastic waves in a 2D billiard and in a disordered plate by means of laser interferometry. Despite the complexity of such configurations, the negatively reflected wave field focuses back towards the initial source location, thereby mimicking a phase conjugation operation while being a fully passive process. The super-focusing capability of negative reflection is also highlighted in a monochromatic regime. The negative reflection phenomenon is not restricted to guided elastic waves since it can occur in zero-gap systems such as photonic crystals, chiral metamaterials or graphene. Negative reflection can thus become a tool of choice for the control of waves in all fields of wave physics.
在复杂介质中，波的传播可以通过两种方式来控制：一是驯服入射到介质上的波场，二是通过精心设计介质，迫使波沿着所需路径传播。这两种不同的策略催生了诸如时间反转或负折射等引人入胜的概念。在此，我们展示了这两个过程是如何通过负反射现象紧密联系在一起的。负反射镜能将具有正相速度的波转换为具有负相速度的波，反之亦然。在本文中，我们借助激光干涉测量法，在二维台球模型和无序平板中用弹性波对这一现象进行了实验验证。尽管此类结构很复杂，但负反射波场会聚焦回到初始源位置，从而模拟了相位共轭操作，同时这是一个完全被动的过程。在单色状态下，负反射的超聚焦能力也得到了凸显。负反射现象并不局限于导波弹性波，因为它也能在诸如光子晶体、手性超材料或石墨烯等零带隙系统中出现。因此，负反射可能会成为波动物理学所有领域中控制波的首选工具。
