Towards anti-causal Green’s function for three-dimensional sub-diffraction focusing
发布时间：2025-04-30
点击次数：
- 发布时间：
- 2025-04-30
- 论文名称：
- Towards anti-causal Green’s function for three-dimensional sub-diffraction focusing
- 发表刊物：
- Nature Physics
- 摘要：
- In causal physics, the causal Green’s function describes the radiation of a point source. Its counterpart, the anti-causal Green’s function, depicts a spherically converging wave. However, in free space, any converging wave must be followed by a diverging one. Their interference gives rise to the diffraction limit that constrains the smallest possible dimension of a wave’s focal spot in free space, which is half the wavelength. Here, we show with three-dimensional acoustic experiments that we can realize a stand-alone anti-causal Green’s function in a large portion of space up to a subwavelength distance from the focus point by introducing a near-perfect absorber for spherical waves at the focus. We build this subwavelength absorber based on membrane-type acoustic metamaterial, and experimentally demonstrate focusing of spherical waves beyond the diffraction limit.
- 合写作者：
- Guancong Ma, Xiying Fan, Fuyin Ma, Julien de Rosny, Ping Sheng and Mathias Fink
- 卷号：
- 4
- 页面范围：
- 1-6
- 是否译文：
- 否
- 发表时间：
- 2018-03-19