Active THz polarization laser imaging

主动太赫兹偏振激光成像

• 批准号: 1610892
• 负责人: Benjamin Williams
• 金额: $ 33万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2020-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1610892&HistoricalAwards=false
• 关键词: Active; THz; polarization; laser; imaging

Light is an electromagnetic wave whose properties are described not only by the amplitude of the wave (i.e. its intensity) and its wavelength (i.e. its color), but also its polarization (i.e. direction of the electric field). Where most types of imaging use the intensity and/or wavelength as contrast mechanisms and ignore the polarization, there is often much information to be obtained by examining the polarization state of the light reflected or transmitted from a scene. Compared to other regions of the electromagnetic spectrum, in the terahertz frequency range (300 GHz-10 THz), polarization has been underutilized as a contrast mechanism for imaging. A major application of terahertz radiation is for non-destructive evaluation due its ability to penetrate many visibly opaque materials for example pharmaceutical tablet coatings, foams, paints, covered art and antiquities. Polarization can potentially provide significant improvement in the utility of terahertz imaging for non-destructive evaluation due to its ability provide information about material birefringence, surface features, shape, roughness, edge detail, and chirality. The theme of this research is the development of a new type of terahertz laser in which the polarization of the emitted light can be chosen and switched rapidly, by electronic control, without moving parts. The approach is based upon the adaptation of antenna design concepts from the microwave frequency range, and combining them with terahertz laser design. The developed lasers will then be used as illumination sources for polarization-based imaging, with a particular emphasis on evaluating their suitability for non-destructive evaluation applications. As a part of the project, the research will train graduate and undergraduate students, and will support recruitment and retention of underrepresented minorities to engineering through the PI's participation in a targeted research project course.The objective of this research is the development of terahertz active polarization imaging based upon THz quantum-cascade lasers (QCLs) as an illumination source. First, an innovative scheme is proposed where the output polarization of QCLs can be modulated electronically. This scheme is based upon terahertz metamaterial antennas or phased arrays of lasers that are designed to radiate with overlapping beams, but with orthogonal polarization. By controlling the relative phase of the laser radiation, the output polarization can be dynamically switched between various linear and circular polarization states. This will allow more rapid and stable modulation of the output polarization compared to current schemes based upon rotating polarizers and waveplates, which in turn will allow faster data collection with reduced noise and a more compact and lightweight system. Second, the developed QCLs will be applied to polarimetric imaging in several schemes, and their performance will be quantified versus conventional techniques. The developed technology has the potential to impact many nondestructive evaluation applications including corrosion detection and monitoring, bioimaging, security screening and illicit material detection, and manufacturing process quality control.

光是一种电磁波，其特性不仅由波的振幅（即其强度）和波长（即其颜色）来描述，而且还由其偏振（即电场的方向）来描述。在大多数类型的成像使用强度和/或波长作为对比机制并忽略偏振的情况下，通常可以通过检查从场景反射或透射的光的偏振状态来获得很多信息。与电磁频谱的其他区域相比，在太赫兹频率范围 (300 GHz-10 THz) 中，偏振作为成像对比机制并未得到充分利用。太赫兹辐射的主要应用是无损评估，因为它能够穿透许多可见不透明的材料，例如药片涂层、泡沫、油漆、覆盖艺术品和古董。偏振可以显着提高太赫兹成像在无损评估中的实用性，因为它能够提供有关材料双折射、表面特征、形状、粗糙度、边缘细节和手性的信息。 这项研究的主题是开发一种新型太赫兹激光器，可以通过电子控制快速选择和切换发射光的偏振，无需移动部件。该方法基于微波频率范围的天线设计概念的改编，并将其与太赫兹激光器设计相结合。所开发的激光器将用作基于偏振的成像的照明源，特别强调评估它们对无损评估应用的适用性。作为该项目的一部分，该研究将培训研究生和本科生，并通过 PI 参与有针对性的研究项目课程，支持招募和保留代表性不足的少数群体。这项研究的目标是开发太赫兹主动偏振基于太赫兹量子级联激光器（QCL）作为照明源的成像。 首先，提出了一种创新方案，可以通过电子方式调制 QCL 的输出偏振。该方案基于太赫兹超材料天线或激光相控阵，设计用于以重叠光束辐射，但具有正交偏振。通过控制激光辐射的相对相位，输出偏振可以在各种线偏振和圆偏振状态之间动态切换。与基于旋转偏振器和波片的当前方案相比，这将允许更快速、更稳定地调制输出偏振，进而允许更快的数据收集、更低的噪声和更紧凑、更轻的系统。其次，所开发的 QCL 将应用于多种方案的偏振成像，并且其性能将与传统技术相比进行量化。所开发的技术有可能影响许多无损评估应用，包括腐蚀检测和监测、生物成像、安全筛查和非法材料检测以及制造过程质量控制。