Terahertz ranging and imaging of arbitrarily shaped objects at unknown distances with monolithic mode-locked laser diodes

使用单片锁模激光二极管对未知距离的任意形状物体进行太赫兹测距和成像

• 批准号: 494582767
• 负责人: Professor Dr.-Ing. Jan C. Balzer
• 金额: --
• 依托单位: Fachgebiet Nachrichtentechnische Systeme (NTS)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/494582767?language=en
• 关键词: Terahertz; ranging; imaging; arbitrarily; shaped

The ongoing development of THz technology, in particular compact and user-friendly THz systems, is increasingly opening up new fields of application. In addition to industrial quality control and communications engineering, THz systems will be increasingly used in user-defined scenarios in the future, such as in the field of art conservation and cultural heritage research. For example, THz imaging as a complementary tool to X-rays has already provided new insights into important works of art and ancient human remains. However, the THz systems used, which are based on fiber lasers, can only be used with great effort during on-site examinations. Furthermore, they are either only suitable for imaging planar surfaces or require complex mechanics such as a robotic arm. Here, the shape and position of the object must be known before the actual measurement process, so that currently only measurements in the laboratory are feasible.Within the scope of this project, both challenges are to be overcome. On the one hand, a compact THz system is to be developed, which is operated by a mode-locked laser diode. The high repetition rate of the laser diode allows the use of a short delay unit and the detection of THz pulses from any distance. The high stability of the mode-locked laser diodes is exploited to reconstruct the time axis of the THz signal with a high accuracy. This allows the use of simple and compact delay units without sacrificing precision. Remaining systematic errors of the delay unit are corrected by a genetic algorithm. A programmable optical filter is used to optimize the bandwidth and signal-to-noise ratio of the system. The ambiguity in the range measurement caused by the high repetition rate is resolved by two methods. One is to use the phase of the lock-in amplifier to determine the length of the THz free space path. Another approach relies on amplitude modulation of the optical signal feeding the THz optoelectronic antennas. A frequency sweep can also be used to determine the distance between the THz system and the target. In order to image objects and hidden objects of arbitrary shape without a priori knowledge, a divergent beam based method is adapted for THz systems with ultra-high repetition rate. Here, image reconstruction is realized in a post-processing step using Kirchhoff migration.As a result of this project, methods for a THz imaging system are developed, which in principle can be completely integrated. With the algorithms developed for this system, objects of arbitrary shape can be measured outside an optical laboratory.

太赫兹技术的持续发展，特别是紧凑和用户友好的太赫兹系统，正在日益开辟新的应用领域。除了工业质量控制和通信工程之外，太赫兹系统将在未来越来越多地用于用户自定义场景，例如艺术保护和文化遗产研究领域。例如，太赫兹成像作为x射线的补充工具，已经为重要的艺术作品和古代人类遗骸提供了新的见解。然而，所使用的基于光纤激光器的太赫兹系统只能在现场检查时使用。此外，它们要么只适用于平面成像，要么需要复杂的力学，如机械臂。在这里，在实际测量过程之前必须知道物体的形状和位置，因此目前只有在实验室中的测量是可行的。在这个项目的范围内，这两个挑战都需要克服。一方面，要开发一个紧凑的太赫兹系统，该系统由锁模激光二极管操作。激光二极管的高重复率允许使用短延迟单元和从任何距离检测太赫兹脉冲。利用锁模激光二极管的高稳定性，可以高精度地重建太赫兹信号的时间轴。这允许使用简单和紧凑的延迟单元而不牺牲精度。通过遗传算法对延迟单元的剩余系统误差进行校正。采用可编程光滤波器对系统的带宽和信噪比进行优化。采用两种方法解决了高重复率引起的距离测量模糊问题。一种是利用锁相放大器的相位来确定太赫兹自由空间路径的长度。另一种方法依赖于光信号的幅度调制馈送太赫兹光电天线。频率扫描也可以用来确定太赫兹系统和目标之间的距离。为了在没有先验知识的情况下对任意形状的物体和隐藏物体进行成像，提出了一种基于发散光束的方法，适用于具有超高重复率的太赫兹系统。在这里，图像重建是通过基尔霍夫迁移在后处理步骤中实现的。由于这个项目，开发了太赫兹成像系统的方法，原则上可以完全集成。利用为该系统开发的算法，可以在光学实验室之外测量任意形状的物体。