Electrically tunable cholesteric optical filters

一般描述。光学成像是我们与周围世界互动的基石。在某些情况下，这种互动不需要任何特殊的工具，因为大自然为人类提供了视觉力量。在生物医学和化学分析、食品和农业、航空航天和国防等领域的技术应用越来越依赖于控制光的透射率和反射率的能力，以区分不同的光的“颜色”。该项目建议开发简单紧凑的设备，可以在从紫外线到可见光和红外光谱的广泛范围内选择性地反射或传输不同颜色的光。这个想法是使用一种新发现的具有电控周期性的液晶结构。该装置代表了夹在两个透明电极之间的液晶薄膜。通过改变施加的电压，人们改变了结构的周期，从而改变了由薄膜传输或反射的光的颜色。该设备将帮助拍摄肉眼无法查看的细节。其目的是从实验和理论上表征这些液晶薄膜在不同器件几何形状下的电光性能，以探索它们作为可调谐反射器、衍射光栅、光衰减器和光偏振旋转器的作用。该项目在从现有技术(如改进的显示器)到新技术(如可调“智能窗”、快门、衰减器、可调激光、光学限幅器、偏振旋转器)等领域具有巨大的社会效益。拟议的研究为研究生和本科生提供了一个极好的平台，让他们学习材料科学、电光现象、光学和高级显微镜。技术说明。目前光学成像领域，特别是多光谱成像领域的挑战可以表述为两项任务：(1)找到容易地选择和调整光谱波段参数的方法，例如峰值波长和带宽；(2)使光谱成像变得紧凑和负担得起。该项目提出了基于具有斜螺旋结构的胆甾相液晶(LCS)的新型电调谐滤光器，以满足上述两个方面的要求。最近发现的ChOH，其特点是对光轴(分子取向的导向器)进行单模调制，其周期可以通过外加电场进行调节。其智力意义在于揭示了ChOCH电光在从UV到Vis和IR的广泛光谱范围内的潜力。具有指向矢周期调制但分子密度均匀的斜螺旋结构在液晶和软物质领域是新出现的。它的前身是所谓的扭曲弯曲向列相NTB，它是几年前才发现的，由于人们对斜螺旋结构的精细细节及其对外场的响应还没有很好的了解，目前NTB的研究正在爆炸性地增长。这项拟议的研究将使人们对ChOH的结构如何由外加电场和限制几何形状进行塑造以及如何将其用于设计和制造新一代电可调光学元件，如滤光器、光栅、偏振旋转器、衰减器等产生新的认识。电调周期是液晶电光响应的一种新模式。该项目的变革性价值在于有可能为可调谐电光器件提供新的设计概念，可在从UV到Vis和IR的广泛光谱范围内运行。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

General description. Optical imaging is a cornerstone of our interaction with the surrounding world. In some cases, this interaction does not require any special instruments, as Nature provided humans with power of sight. Technological applications in areas such as biomedical and chemical analysis, food and agriculture, aerospace and defense increasingly rely on the ability to control light transmittance and reflectance, to separate different "colors" of light. The project proposes to develop simple and compact devices that could selectively reflect or transmit different colors of light in a broad range from ultraviolet to visible and infrared parts of the spectrum. The idea is to use a newly discovered liquid crystal structure with electrically controlled periodicity. The device represents a thin film of the liquid crystal sandwiched between two transparent electrodes. By changing the applied voltage, one changes the period of the structure and thus s the colors of light transmitted or reflected by the film. The device will help to image details that are not accessible by a human eye. The objectives are to characterize experimentally and theoretically electro-optical performance of these liquid crystalline films in various device geometries with controlled direction of light propagation, to explore them as tunable reflectors, diffraction gratings, light attenuators, and rotators of light polarization. The project has the potential for enormous societal benefits in areas ranging from existing technologies (such as improved displays) to new technologies, such as tunable "smart windows", shutters, attenuators, tunable lasers, optical limiters, polarization rotators. The proposed research provides a superb platform to educate students at graduate and undergraduate levels in materials science, electro-optic phenomena, optics, and advanced microscopy. Technical description. The current challenge in the field of optical imaging and especially multispectral imaging can be formulated as a two-fold task: (1) to find the means to easily select and adjust the spectral bands parameters such as peak wavelength and bandwidth and (2) to make the spectral imaging compact and affordable. This project proposes to develop new electrically tunable optical filters based on cholesteric liquid crystals (LCs) with oblique helicoidal structure (ChOH) that would fulfill both of the requirements above. ChOH, discovered very recently, features a single-mode modulation of the optic axis (the director of molecular orientations) with a period that is tunable by the applied electric field. The intellectual significance is in unveiling the potential of ChOH electro-optics in a broad spectral range from UV to Vis and IR. The oblique helicoidal structure of ChOH with periodic modulation of the director but homogeneous molecular density is new to the field of LCs and soft matter in general. Its predecessor, the so-called twist-bend nematic phase NTB, has been discovered only a few years ago and is currently enjoying an explosive growth of research as the fine details of the oblique helicoidal structures and their response to the external fields are not understood well. The proposed research will result in the new knowledge of how the structure of ChOH is shaped by the externally applied electric field and confinement geometry and how ChOH can be used in the design and fabrication of the new generation of electrically tunable optical elements such as filters, gratings, polarization rotators, attenuators. The electrically adjustable period of ChOH represents a new mode of the electro-optical response of LCs. The transformative value of the project is in the potential for new design concepts for tunable electro-optical devices performing in a broad spectral range from UV to Vis and IR.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.