MRI: Development of a Holographic Nanoscale Optics Instrument

非技术性光学(或光学)显微镜可以说是有史以来最成功的非侵入性微观世界检查技术之一。罗伯特·胡克创造了“细胞”一词，用来描述他在17世纪首次通过显微镜观察到的软木的亚结构。在过去的一个世纪里，已经开发了各种复杂的方法，这些方法今天提供了观察迁移细胞、检查亚细胞结构的分布、绘制基因表达图或根据样本的分子结构编码形成“化学图像”的能力。尽管光学显微镜取得了巨大的成功，但它在分辨小于几百纳米的特征方面的能力从根本上说是有限的。具体地说，衍射极限会导致来自物体中各点的光线在通过透镜传播时扩散开来，从而使放大后的图像变得模糊。近场显微镜克服了这些限制，它将一个光学探头放置在距离物体几十纳米的地方，并在发射或散射的光经历衍射之前对其进行采样。波士顿大学的研究人员正在建造一种多功能近场显微镜，为当地和地区用户提供10纳米量级的光学分辨率。该仪器正在推动一系列重要的研究项目，包括(I)可揭示阿尔茨海默氏症等疾病的蛋白质折叠行为的研究；(Ii)激光光源新材料的开发；(Iii)用于下一代电子产品的设计石墨烯等单原子厚层性质的方法；(Iv)对纳米尺度上的光流动进行控制的方法，这对新的光学传感器和通信技术至关重要。波士顿大学的项目还吸引了女性和少数族裔本科生参与尖端研究。由于在纳米尺度上“看到”物体的能力对年轻人来说是一个强大的动力，该团队正在与北卡罗来纳大学为城市高中生提供的为期7周的向上绑定数学科学实习大学预科项目合作。暑期每个周三，学生们都会进行纳米技术动手实验，并使用新的显微镜观察纳米世界。光学显微镜可以说是有史以来对显微世界进行非侵入性检查的最成功的技术之一，但受衍射极限的限制，基本上仅限于100 nm或更长的长度尺度。近场显微镜通过将光源或探头放置到样品的近光场中，将非传播或消逝模式耦合到远场传播模式以进行收集，从而克服了这一点。虽然有5到6家公司销售近场显微镜，但所有公司的能力都有限。波士顿大学的研究人员正在建造一种集成到原子力显微镜中的多功能全息纳米级光学仪器，将弹性散射、拉曼和荧光的近场光谱结合在一起，在很大的波长范围内。该仪器可在透射式和后向散射式两种几何结构下运行，并包括用于相位分辨近场成像的干涉测量，以绘制3D场响应图，提供对推进复杂研究问题至关重要的灵活性和灵巧性。该仪器使波士顿大学和地区性大学的研究人员能够研究等离子体、生物物理学、石墨烯和其他二维(2D)晶膜物理中的纳米级光学现象。等离子体研究正在探索热点、局域态密度，特别是预测将在金属和介电组件之间的界面上出现的相位奇异性。在石墨烯、MoS2和hBN的应变工程2D晶体中，北卡罗来纳大学的研究人员正在探索原子尺度的摩擦和绘制应变诱导的伪磁场的令人兴奋的可能性。在锗半导体纳米膜的研究中，局域光学响应可以证实和帮助设计具有直接带隙的纳米器件。在生物物理学中，长波尖端增强的近场显微镜可以提供前所未有的内在振动模式的图像，能够进行亚细胞分类和重要蛋白质的局部存在。

Non-technicalOptical (or light) microscopy is arguably one of the most successful techniques for the non-invasive examination of the microscopic world ever created. Robert Hooke coined the term "cells" to describe the substructure of cork he first observed through a microscope in the 17th century. Over the past century a variety of sophisticated methods have been developed that today provide the ability to observe migrating cells, examine the distribution of subcellular structures, map the expression of genes, or form "chemical images" coded according to the molecular structure of the sample. Despite its immense success, optical microscopy is fundamentally limited in its ability to resolve features less than a few hundred nanometers. Specifically, the diffraction limit causes light from points in an object to spread out as it propagates through a lens, thereby blurring images as they are magnified. Near-field microscopy overcomes these limitations by placing an optical probe a few tens of nanometers away from the object and sampling the emitted or scattered light before it experiences diffraction. Boston University researchers are building a versatile near-field microscope providing local and regional users with access to optical resolution on the order of 10 nanometers. The instrument is enabling a range of important research thrusts including (i) studies of protein folding behavior that can shed light on conditions such as Alzheimer's; (ii) the development of new materials for laser sources; (iii) methods for engineering the properties of single atomic thick layers like graphene for next-generation electronics and; (iv) methods for controlling the flow of light on nanometer length scales, important for new optical sensors and communications technologies. The BU project is also engaging women and underrepresented minority undergraduate students in cutting-edge research. Since the ability to "see" objects at the nanoscale can be a powerful motivator for a young mind, the team is working with BU's Upward Bound Math Science 7-week residency college prep program for urban high school students. Every Wednesday in the summer, students perform nanotechnology hands-on experiments and use the new microscope to observe the nano-world. Technical DescriptionOptical microscopy is arguably one of the most successful techniques for non-invasive examination of the microscopic world ever created, but is fundamentally limited to length scales of 100 nm or more by the diffraction limit. Near-field microscopy overcomes this by placing a source or probe into the near optical field of a sample to couple the non-propagating or evanescent modes into far-field propagating modes for collection. While there are 5 or 6 companies that sell near-field microscopes, all are limited in capability. Boston University researchers are building a versatile holographic nanoscale optics instrument integrated into an atomic force microscope, combining near-field spectroscopies of elastic scattering, Raman and fluorescence over a wide wavelength range. The instrument operates in both transmission and back-scattering geometries, and includes interferometry for phase-resolved near-field imaging to map 3D field response, providing the flexibility and dexterity that are critical to advance complex research problems. The instrument enables researchers at BU and regional universities to investigate nanoscale optical phenomena in plasmonics, biophysics, and graphene and other two-dimensional (2D) crystal membrane physics. Plasmonic studies are exploring hot spots, local density of states and in particular, phase singularities predicted to occur at the interface between metal and dielectric components. In strain engineered 2D crystals of graphene, MoS2 and hBN, researchers at BU are exploring atomic-scale friction and the exciting possibility of mapping strain-induced pseudo-magnetic fields. In studies of Germanium semiconductor nanomembranes, local optical response can confirm and help engineer nano-devices with direct bandgaps. And in biophysics, long-wavelength tip-enhanced near-field microscopy can provide unprecedented images of intrinsic vibrational modes capable of sub-cellular classification and local presence of important proteins.