Brownian Transport Through Modulated Potential Energy Landscapes

该计划的重点是如何通过动态全息光镊创建广泛的势能景观胶体粒子移动。 通过调制势能景观的传输是凝聚态物理学中的一个经典问题，在不同的系统中出现变体，如通过II型超导体的通量流，约瑟夫森结中的准粒子隧穿和生物分子马达中的游行。 虽然我们对一维周期势中的输运有很多了解，但关于更高维度中的调制布朗输运，特别是在非周期、准周期、随机和时变景观中，还有更多的东西有待了解，所有这些都在自然和工业环境中占有重要地位。 以前理解这些过程的努力一直受到难以控制大多数相关系统的势能景观的阻碍，同时跟踪其微观组件的运动。 动态全息光镊提供了一个独特的机会，构建任意的一维，二维和三维的势能景观微米级的胶体粒子投影到几千个光阱在任何所需的配置。 与大多数其他模型系统不同，胶体颗粒的微观运动可以使用数字视频显微镜精确跟踪。 光学操纵和高分辨率粒子跟踪的组合提供了一个非常灵活和良好的特征模型系统，用于研究驱动调制布朗输运，不仅对于单个粒子，而且对于强相互作用的粒子系统。 除了从这些研究中获得的基本知识外，介观输运的特殊应用有望在纳米技术、生物技术和光子学中立即得到实际应用。 DNA分子如何穿过凝胶？ 解决这些问题需要对物体如何穿越复杂的势能景观有新的基本见解。 这些问题的答案将对高温超导、药物发现、纳米技术和工程等不同领域产生直接的实际影响。 该计划结合了最先进的显微操作，使最近推出的全息光镊（HOTs）与精确的数字视频显微镜提供这样的见解。 该计划的核心是由HOT的能力，从一个普通的激光束创建任意定制设计的势能景观。 该技术使用计算机生成的全息图将光束制作成数千个独立的光学陷阱，每个陷阱都可以在计算机控制下在三维空间中独立移动。 如果把一个光阱比作《星星迷航》中的牵引光束，那么全息光镊就更像全息甲板。 微米尺度的胶体粒子被驱动穿过这种光的网格，追踪出长期存在的基础物理问题的解决方案。 在这样做的过程中，它们也为实际应用提供了基础，例如使用光分选蛋白质，DNA，纳米团簇和活细胞。 该计划所基于的新技术是在高中和本科生以及研究生和博士后的直接参与下开发的。 这些学生在这些方法方面的独特培训帮助他们在一流学校获得职位，并在工业和学术界长期就业。 该计划的方法已获得专利，这些专利导致了光学显微操作新产业的基础。 行业和各级学生的这种实质性参与将继续成为该计划的中心主题。

This program focuses on how colloidal particles move through extensive potential energy landscapes created with dynamic holographic optical tweezers. Transport through modulated potential energy landscapes is a classic problem in condensed matter physics, with variants arising in systems as diverse as flux flow through type-II superconductors, quasiparticle tunneling in Josephson junctions and procession in biological molecular motors. While much is known about transport in one-dimensional periodic potentials, much more remains to be understood regarding modulated Brownian transport in higher dimensions, particularly in aperiodic, quasiperiodic, random, and time-varying landscapes, all of which figure heavily in natural and industrial settings. Previous efforts to understand such processes have been hampered by the difficulty of controlling most relevant systems' potential energy landscapes while tracking their microscopic components' motions. Dynamic holographic optical tweezers present a unique opportunity to construct arbitrary one-, two-, and three-dimensional potential energy landscapes for micrometer-scale colloidal particles by projecting up to several thousand optical traps in any desired configuration. Unlike most other model systems, colloidal particles' microscopic motions can be tracked with exquisite accuracy using digital video microscopy. The combination of optical manipulation and high-resolution particle tracking provides an extraordinarily flexible and well-characterized model system for studying driven modulated Brownian transport, not only for single particles but also for strongly interacting systems of particles. In addition to the fundamental knowledge gained from such studies, the particular application to mesoscopic transport promises immediate practical applications in nanotechnology, biotechnology, and photonics.How does an electron find its way through the labyrinth of a metallic glass? How does a DNA molecule thread through a gel? Answering such questions requires a new fundamental insights into how objects traverse complicated potential energy landscapes. And the answers will have immediate practical ramifications for fields as diverse as high-temperature superconductivity, drug discovery, nanotechnology and engineering. This program combines state-of-the-art micromanipulation made possible by the recent introduction of holographic optical tweezers (HOTs) with precision digital video microscopy to provide just such insights. The heart of this program is provided by HOT's ability to create arbitrary custom-designed potential energy landscapes from an ordinary beam of laser light. The technique uses computer-generated holograms to craft the beam into thousands of individual optical traps, each of which can be moved independently in three dimensions under computer control. If a single optical trap can be likened to Star Trek's tractor beam, then holographic optical tweezers more closely resemble the holodeck. Micrometer-scale colloidal particles driven through such latticeworks of light trace out solutions to long-standing fundamental physics questions. In so doing, they also provide the basis for practical applications such as sorting proteins, DNA, nanoclusters, and living cells using light. The new techniques on which this program is based were developed with direct involvement of high school and undergraduate students, as well as graduate students and postdocs. These students' unique training in these methods has helped them to land positions in top-rated schools, as well as long-term employment in industry and academia. This program's methods have been patented, and the patents have led to the foundation of a new industry in optical micromanipulation. Such substantive involvement of industry and students at all levels will continue to be a central theme of this program.