Random anti-lasing through coherent perfect absorption in a disordered medium
Random anti-lasing through coherent perfect absorption in a disordered medium
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DOI：
10.1038/s41586-019-0971-3
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发表时间：
2019-03-21
期刊：
影响因子：
64.8
通讯作者：
Rotter, Stefan
中科院分区：
文献类型：
--
作者：
Pichler, Kevin;Kuhmayer, Matthias;Rotter, Stefan
非厄米波工程是一个最近和快速发展的领域，检查基本和面向应用的现象（1-7）。一种这样的现象是相干完全吸收（8-11）-通常被称为“反激光”的效应，因为它对应于在激光阈值处辐射的相干发射的时间反转过程（其中所有辐射损耗被光学增益精确地平衡）。相干完美吸收体（CPA）已经在几种装置中实验实现（10-18），但在无序介质（没有工程结构的介质）中的CPA除外。这样的“随机CPA”将是“随机激光器”的时间反转（19，20），其中光通过无序内部的多次散射而共振增强。由于这种散射过程的复杂性，随机激光器发射的光场在空间上也是复杂的，并且不像常规激光束那样聚焦。因此，实现随机CPA（或“随机反激光”）是具有挑战性的，因为它需要在其所有自由度上对这样的光场进行时间反转的等效物，以产生当撞击在无序介质上时被完全吸收的相干辐射。在这里，我们使用微波技术来建立一个随机的反激光，并证明它的能力，吸收适当的工程入射辐射场与近乎完美的效率。由于我们确定这些场模式的方法仅基于无序介质散射特性的远场测量，因此它可能适用于波需要完美聚焦，路由或吸收的其他应用。
Non-Hermitian wave engineering is a recent and fast-moving field that examines both fundamental and application-oriented phenomena(1-7). One such phenomenon is coherent perfect absorption(8-11)-an effect commonly referred to as 'anti-lasing' because it corresponds to the time-reversed process of coherent emission of radiation at the lasing threshold (where all radiation losses are exactly balanced by the optical gain). Coherent perfect absorbers (CPAs) have been experimentally realized in several setups(10-18), with the notable exception of a CPA in a disordered medium (a medium without engineered structure). Such a 'random CPA' would be the time-reverse of a 'random laser'(19,20), in which light is resonantly enhanced by multiple scattering inside a disorder. Because of the complexity of this scattering process, the light field emitted by a random laser is also spatially complex and not focused like a regular laser beam. Realizing a random CPA (or 'random anti-laser') is therefore challenging because it requires the equivalent of time-reversing such a light field in all its degrees of freedom to create coherent radiation that is perfectly absorbed when impinging on a disordered medium. Here we use microwave technology to build a random anti-laser and demonstrate its ability to absorb suitably engineered incoming radiation fields with near-perfect efficiency. Because our approach to determining these field patterns is based solely on far-field measurements of the scattering properties of a disordered medium, it could be suitable for other applications in which waves need to be perfectly focused, routed or absorbed.