EAGER: High-performance Optical-phonon-based Terahertz Sources Operating at Room Temperature

中红外（MIR）到太赫兹（THz）光谱范围具有独特的科学和技术意义，因为它承载了无数分子物种的最强和指纹状吸收线，使其成为开发具有优越选择性和灵敏度的传感技术的理想光谱范围，适用于广泛的应用。量子级联激光器（qcl）由于其结构紧凑、操作方便和输出功率高，目前是该光谱范围内许多应用的首选光源。然而，在太赫兹区域，qcl的性能仍然不足以满足各种实际应用。太赫兹qcl的性能远低于MIR qcl，并且其最高工作温度仍然限制在~200K。此外，目前没有QCL可以在5太赫兹到11太赫兹范围内工作。在这个探索性项目中，我们计划开发一种新型的紧凑，高性能和室温工作的太赫兹源，以覆盖这一“间隙”光谱范围。该器件基于一种未经测试但有前景的新工作原理，该器件的成功演示将对太赫兹源的研究领域产生变革性影响，并实现各种应用。因此，本研究适合NSF EAGER项目。该项目将使研究生和本科生积极参与前沿研究，获得未来在竞争激烈的全球舞台上领导科学研究和技术发展所需的知识、技能、经验和广阔的视野。将研究与教育和外展活动相结合也将是我们工作的重点，旨在使所有年龄组和背景的学生受益，包括那些来自代表性不足群体的学生。技术描述本项目的目标是系统地探索如何基于根本不同的器件工作原理实现新型太赫兹源。该装置的工作原理包括两个关键过程：(1)在多量子阱（mqw）中通过共振子带间跃迁产生光学声子；(2)将产生的光学声子的能量传递到共振太赫兹天线，然后将光子发射到自由空间。由于器件的工作原理对温度不敏感，因此这种太赫兹源应在室温及以上条件下工作良好。mqw和太赫兹天线的设计将进行优化，以使这两个过程都高效，从而实现高的整体能量转换效率，可能比典型的太赫兹qcl高几个数量级。此外，这种太赫兹源具有表面发射结构，因此输出功率随着器件面积的增加而增加。提出的研究也可能使我们获得新的和/或更深入的见解，了解mqw中子带间跃迁，光学声子和光子结构的电磁共振之间相互作用的有趣和复杂的物理。涉及所有三种激发的相互作用尚未被系统地研究过。更好地理解底层物理将指导我们改进设备设计，并可能激励我们追求更先进设备的新可能性。

Title: High-performance Optical-phonon-based Terahertz Sources Operating at Room TemperatureNon-technical DescriptionThe mid-infrared (MIR) to terahertz (THz) spectral range has its unique scientific and technological significance, as it hosts the strongest and fingerprint-like absorption lines of countless molecular species, making it the ideal spectral range for developing sensing technologies with superior selectivity and sensitivity for a broad range of applications. Quantum cascade lasers (QCLs) are currently the preferred light sources for many applications in this spectral range, thanks to their compactness, convenient operation and high output power. However, in the THz region the performance of QCLs is still not sufficient for various real-world applications. THz QCLs have much lower performance than MIR QCLs, and the highest operating temperature of THz QCLs is still limited to ~200K. Furthermore, currently no QCL can operate within the 5 THz to 11THz range. In this exploratory project, we plan to develop a new type of compact, high-performance and room-temperature operating THz sources to cover this "gap" spectral range. The proposed devices are based on an untested but promising new operation principle, and the successful demonstration of such devices will bring transformative impacts to the research field of THz sources and enable various applications. Therefore, the proposed research is suitable for the NSF EAGER program. This project will allow graduate and undergraduate students to actively participate in cutting-edge research, and acquire the knowledge, skills, experiences and broad perspectives necessary for their future leadership in scientific research and technology development on the competitive global stage. Combining research with education and outreach activities will also be a focus of our work, aiming at benefiting students of all age-groups and backgrounds, including those from underrepresented groups.Technical DescriptionThe objective of this project is to systematically explore how to realize a new type of THz sources based on a fundamentally different device operation principle. The device operation principle consists of two key processes: (1) generating optical phonons by resonant inter-subband transitions in multiple-quantum-wells (MQWs), and (2) transferring the energy from the generated optical phonons to resonant THz antennae which then emit photons into free space. As the device operation principle is not sensitive to temperature, such THz sources should operate well at room temperature and above. Designs of the MQWs and the THz antennae will be optimized to make both processes efficient, leading to a high overall energy conversion efficiency which is potentially orders of magnitude higher than that of typical THz QCLs. Moreover, such THz sources have a surface-emitting configuration, so the output power scales up with the device area. The proposed research may also allow us to gain new and/or deeper insights into the interesting and complex physics underlying the interplay between inter-subband transitions in MQWs, optical phonons and electromagnetic resonances of photonic structures. Interactions involving all three excitations have not been systematically studied. A better understanding of the underlying physics will guide us to improve the device design, and may inspire us to pursue new possibilities of more advanced devices.