Advanced terahertz quantum cascade lasers for frequency comb and mode locking operation

在过去的十年里，太赫兹(THz)频率范围(1-10太赫兹，1太赫兹=1E12赫兹)的电磁波受到了高度关注，主要是因为它们有可能给重要的应用带来革命性的变化，其中包括生物化学物种检测、天文光谱学、太赫兹成像和无线光通信。自2002年问世以来，太赫兹量子级联激光器(QCL)以其结构紧凑、效率高、波长稳定性好等优点迅速成为一种很有前途的相干光源，但要将其应用于实际应用还存在很大困难，其中最有希望的就是高性能光谱技术。为了应对这一挑战，拟议的研究计划旨在开发一种基于THzQCL的频率梳设备，以在THz范围内产生稳定而均匀的多波长发射，从而实现高分辨率、易于操作的THz光谱测量。这将为创新奠定基础，这些创新具有更快和低成本地检测危及生命的疾病(如皮肤癌)、在安全检查站更准确和迅速地筛查危险爆炸物以及更广泛和可靠地部署先进环境监测和保护的潜力。 这项拟议的计划旨在解决实现太赫兹技术所固有的根本和技术挑战。这些目标结合了实验和理论方法，将包括1)开发太赫兹QCL金属-金属脊形波导锁相的基本物理基础；2)开发一个可以数值计算材料和波导色散以及器件增益谱的模拟程序包；3)设计一个量子有源区，它可以产生宽而平坦的增益谱，并在很宽的频率范围内形成总色散为零的波导；4)用于频率梳和/或锁模操作的QCL的制造和表征。 这项研究的直接结果将是展示一种新型的太赫兹频率梳状激光器，从长远来看，它可能导致第一个用于高功率和高重复频率工作的被动锁模太赫兹激光器。这一研究将对半导体量子结构中的子带间跃迁和啁啾光栅设计的激光波导中的锁相机制有更深入的了解。制造的设备将在高分辨率太赫兹光谱学、生物和医学、太赫兹通信、太赫兹成像等领域产生影响。这项研究计划也将为HQP带来极好的培训机会，他们将在明天的知识经济中领导创新。

Electromagnetic waves in the terahertz (THz) frequency range (1-10 THz, 1THz = 1E12 Hz) have received intensive attention over the last decade owing primarily to their potential to revolutionize important applications, including, among many others, bio-chemical species detection, astronomical spectroscopy, terahertz imaging and optical wireless communication. Since their inception in 2002, THz quantum cascade lasers (QCLs) have quickly emerged as a promising coherent light source because of their compactness, high efficiency and wavelength tenability; however, there is significant difficulty in properly adapting these devices for practical applications, the most promising of which is high-performance spectroscopy. In response to this challenge, the proposed research program aims to develop a THz QCL-based frequency comb device to generate stable and uniform multiple-wavelength emissions in the THz range, which would allow high-resolution, easy-to-operate THz spectral measurements. This would lay the groundwork for innovations that have strong potential for much faster and low-cost detection of life-threatening diseases (such as skin cancer), more accurate and expeditious screening of dangerous explosives at security checkpoints, and much wider and reliable deployment of advanced environmental monitoring and protection. This proposed program is targeted to tackle the fundamental and technical challenges inherent to bring THz technology to fruition. The objectives combine experimental and theoretical approaches and will include 1) development of a comprehensive knowledge base on the underlying physics of phase locking in the metal-metal ridge waveguide of THz QCLs; 2) development of a simulation package that can numerically calculate the material and waveguide dispersion as well as the gain spectrum of the device; 3) design of a quantum active region that can produce a broad and flat gain spectrum and develop a waveguide with zero overall dispersion over a wide frequency range; 4) fabrication and characterization of QCLs for frequency comb and/or mode-locking operation. The direct outcome of this research will be the demonstration of a novel terahertz frequency comb laser, which could, in the longer term, lead to the first passive mode-locked THz lasers for high power and high repetition rate operation. The research will develop an in-depth understanding of intersubband transition in semiconductor quantum structures and phase-locking mechanisms in laser waveguide with chirped grating designs. Fabricated devices will carry over impacts in the areas of high-resolution terahertz spectroscopy, biological and medical sciences, terahertz communication, terahertz imaging. The research program will also bring to bear excellent training opportunities for HQP who will lead innovation in tomorrow's knowledge-based economy.