基于人工微纳结构的平板衍射透镜

Planar Diffractive Lenses with Artificial Micro/Nano-Structures

现代显微镜中的物镜受限于瑞利衍射极限,其分辨率不能满足生物成像、材料科学以及光刻等领域的需求。目前,突破瑞利衍射极限的方法可分为近场(如扫描近场光学显微镜、超透镜、微球透镜)和远场(如受激辐射损耗显微镜、光激活定位显微镜、随机光学重建显微镜)方法。然而,前者利用纳米探针散射物体表面一个波长范围内的倏逝波,极具挑战性;而后者对样品有选择性,只适用于荧光分子样品,且会对样品造成损伤。近年来,平板透镜利用波带片、光子筛以及梯度超构表面等人工微纳结构来控制光的衍射,具有小型化、高数值孔径、大焦深、亚衍射极限聚焦等功能,为远场无标记超分辨率成像提供了一个可行的解决方案。本文从衍射聚焦光学的统一理论出发,总结平面衍射透镜的最新进展,揭示基于光场调控实现纳米聚焦的物理机制,介绍平板衍射透镜的设计原理、光学性能、微纳结构特性和材料影响,详细讨论平板衍射透镜的光学像差(如离轴像差和色差)及其校正,平板衍射透镜在纳米成像、光刻以及光电子能谱仪中的应用,最后展望其未来的发展方向和机遇。

Traditional objective lenses based on the refraction of light in modern microscopy are restricted by Rayleigh diffraction limit,and its resolution is insufficient in various applications such as biological imaging,materials science and nanolithography.The existing methods to overcome this limit can be categorized into near-field(e.g.,scanning near-field optical microscopy,superlens and microsphere lens)and far-field(e.g.,stimulated emission depletion microscopy,photoactivated localization microscopy and stochastic optical reconstruction microscopy)approaches.However,the former operates in the challenging near-field mode using the nanoprobe to scatter the evanescent wave existing in a wavelength range of the object surface,and the latter have a selective dependence on fluorescent specimen that needs labeling in advance,which might damage the sample.Recently,through manipulating the diffraction of light with artificial micro/nano structure such as zone plate,photon-sieve and gradient metasurfaces,some miniaturized and planar lenses have been reported with intriguing functionalities such as ultrahigh numerical aperture,large depth of focus,and sub-diffraction-limit focusing at far field,thereby allowing a viable solution for the label-free super-resolution imaging.Here,recent advances in planar diffractive lenses(PDLs)are reviewed from a united theoretical account on diffraction-based focusing optics,and the underlying physics of nanofocusing via controlling interference of light is revealed.Design principle,optical performance of PDLs and their dependence on the micro-/nano-structures and materials will be presented.Optical aberration such as off-axis and chromatic aberration is introduced together with consistent efforts for aberration correction.Furthermore,a detailed tutorial about applying these planar lenses integrated in confocal scanning microscopy for nanoimaging is provided,meanwhile the applications in nanolithography and photoelectron spectrometer is introduced.Finally,the conclusion and outlook regarding future development toward practical applications is presented.