CIF: Small: Impact of radiation trapping on sensing and communication systems in the THz, infrared, and optical regime - foundations, challenges, and opportunities

当电磁辐射通过气体发送时，特定的频率可以被吸收，然后重新发射。重新发射的辐射可以在气体中的其他地方被重新吸收，在那里重新发射，等等。这种吸收/重新发射被称为“辐射捕获”。因为每个吸收/再发射引起延迟并且可以改变方向以及引起轻微的频率变化，所以辐射捕获改变辐射的基本特性-换句话说，到达检测器的辐射具有不同于最初入射在气体上的辐射的特性的特性。如上所述，辐射捕获主要发生在特定的（非常高的）频率。随着现代无线系统向越来越高的频率发展，因此存在更多辐射捕获重要的情况。在这些频率范围内的无线系统可以用于通信、感测或两者。在这些情况下，分析辐射捕获的影响是非常重要的，无论是简单地评估其影响，找到减轻其有害影响的方法，还是积极地利用它。本项目旨在深入研究辐射捕获的基本原理及其对下一代无线通信和传感的影响。这些调查的结果将为这些超高频区域的未来无线系统设计奠定基础，并将广泛传播。此外，还计划开展重要的外联活动，以扩大对这一研究领域的参与。辐射俘获过程对从气体中出现的共振辐射的性质具有重要影响。首先，线形被扭曲：由于吸收线中心频率处的光子“看到”高吸收系数，到达探测器的概率较低，而线形“翅膀”中的光子更容易逃逸。其次，出现的辐射受到延迟色散、频率色散（重新发射的频率从吸收的频率偏移）和空间色散（光子可以在任何方向重新发射，尽管方向色散和频率色散之间可能存在非平凡的关系）的影响。该项目将从研究共振辐射与分子跃迁的相互作用以及轨道角动量（OAM）辐射与原子和分子之间的相互作用开始。辐射俘获的基本方程，Holstein方程，将研究的条件下，实际上是相关的传输（地球）大气的解决方法。 然后，该项目将研究诱捕如何影响传感系统。最后，通信系统，包括多载波和单载波系统的影响，将进行调查。该项目采用跨学科方法，结合原子/分子物理学、化学物理学、通信理论、无线系统设计和实验设计的见解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

When electromagnetic radiation is sent through a gas, specific frequencies can be absorbed, and then re-emitted. The re-emitted radiation can be re-absorbed somewhere else in the gas, re-emitted there, and so on. This absorption/re-emission is known as “radiation trapping”. Because each absorption/re-emission induces a delay and can change the direction as well as induce a slight frequency change, radiation trapping changes the fundamental characteristics of the radiation – in other words, the radiation arriving at a detector has characteristics that are different from that of the radiation that was originally incident on the gas. As mentioned above, radiation trapping happens mainly at specific (very high) frequencies. As modern wireless systems are moving to higher and higher frequencies, there are thus more situations where radiation trapping is important. Wireless systems in those frequency ranges might be used for communication, sensing, or both. In any of these cases, it is important to analyze the impact of radiation trapping – either to simply assess its impact, to find ways to mitigate its detrimental effects, or to actively exploit it. This project pursues an in-depth investigation of both the fundamentals of radiation trapping and its effects on next-generation wireless communications and sensing. The results of these investigations will form a foundation for future wireless system design in these ultra-high-frequency regions, and will be broadly disseminated. Furthermore, significant outreach activities, aimed at broadening the participation in this research area, are planned. The radiation trapping process has important consequences for the properties of the resonance radiation emerging from the gas. Firstly, the line shape is distorted: since photons at the center frequency of the absorption line “see” a high absorption coefficient, the probability of reaching the detector is low, while photons in the “wings” of the line shape can escape more easily. Secondly, the emerging radiation suffers from both delay dispersion, frequency dispersion (the re-emitted frequencies are shifted from the absorbed frequencies), and spatial dispersion (photons can be re-emitted in any direction, though there can be a nontrivial relationship between directional dispersion and frequency dispersion). The project will start by investigating the interaction of resonance radiation with molecular transition and the interaction between Orbital Angular Momenta (OAM) radiation with atoms and molecules. Solution methods for the fundamental equation of radiation trapping, the Holstein equation, will be investigated for conditions that are practically relevant for transmission in (Earth) atmosphere. The project then will investigate how trapping can impact sensing systems. Finally, the implications for communications systems, including multi-carrier and single-carrier systems, will be investigated. The project takes an interdisciplinary approach, combining insights from atomic/molecular physics, chemical physics, communication theory, wireless system design, and experimental design.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.