Low-power Optical Traps Using Anisotropic Metasurfaces: Asymmetric Potential Barriers and Broadband Response
Low-power Optical Traps Using Anisotropic Metasurfaces: Asymmetric Potential Barriers and Broadband Response
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DOI：
10.1103/physrevapplied.15.014018
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
N. K. Paul;J. S. Gómez-Díaz
中科院分区：
文献类型：
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作者：
N. K. Paul;J. S. Gómez-Díaz
我们提出了在线偏振高斯光束照射下，利用定制的各向异性和双曲型准曲面对瑞利粒子的光学俘获。这一平台允许在光束轴上设计光学陷阱，其响应由光散射过程中超受限表面等离子体的定向激发产生的非保守和巨反冲力控制。与设置在大块金属上的光学陷阱相比，所提出的陷阱是宽带的，可以用在亚表面支撑表面等离子体的宽范围内以任何频率振荡的光束来设置。在这一范围内，准表面通过拓扑转变从各向异性椭圆演化为双曲线区域，并使光学陷阱具有独特的空间不对称势分布，局部势垒产生于激发等离子体的动量不平衡，并且增强的势深度允许使用低强度激光稳定地捕获纳米粒子。为了考察该平台的性能，我们在瑞利近似下结合各向异性格林函数建立了基于洛伦兹力的严格形式，并使用Helmholtz-Hodge分解方法计算了非保守力的囚禁势。定制的各向异性和双曲线准表面通常由纳米结构的薄金属层实现，能够使用工作在可见光或红外的低强度激光来捕获和操纵纳米级的粒子，并可能在生物工程、物理和化学中实现广泛的应用。
We propose the optical trapping of Rayleigh particles using tailored anisotropic and hyperbolic metasurfaces illuminated with a linearly polarized Gaussian beam. This platform permits to engineer optical traps at the beam axis with a response governed by nonconservative and giant recoil forces coming from the directional excitation of ultra-confined surface plasmons during the light scattering process. Compared to optical traps set over bulk metals, the proposed traps are broadband in the sense that can be set with beams oscillating at any frequency within the wide range in which the metasurface supports surface plasmons. Over that range, the metasurface evolves from an anisotropic elliptic to a hyperbolic regime through a topological transition and enables optical traps with distinctive spatially asymmetric potential distribution, local potential barriers arising from the momentum imbalance of the excited plasmons, and an enhanced potential depth that permits the stable trapping of nanoparticles using low-intensity laser beams. To investigate the performance of this platform, we develop a rigorous formalism based on the Lorentz force within the Rayleigh approximation combined with anisotropic Green's functions and calculate the trapping potential of nonconservative forces using the Helmholtz-Hodge decomposition method. Tailored anisotropic and hyperbolic metasurfaces, commonly implemented by nanostructuring thin metallic layers, enables using low-intensity laser sources operating in the visible or the IR to trap and manipulate particles at the nanoscale, and may enable a wide range of applications in bioengineering, physics, and chemistry.