Development of THz Laser Frequency Combs

职务名称：太赫兹（THz）激光频率梳非技术性：频率梳可以被视为频域的统治者，它彻底改变了高精度计量和光谱学，2005年诺贝尔物理学奖的一半被授予。在太赫兹（或万亿赫兹，在一个非技术单位），许多物种表现出强烈的和独特的光谱指纹，也就是说，他们吸收或发射强烈的几个特定频率在太赫兹。太赫兹频率梳将是研究这些物种的理想工具。在2014年取得突破性进展之前，太赫兹频率梳已经使用具有非线性产生的大体积泵浦激光器产生。因此，它们非常低效，只能产生低水平的功率（~微瓦）。在我们最近的突破中，我们开发了THz的激光频率梳，产生更高的功率水平（约5 mW）。主要研究者的工作已经在面向广泛社区的媒体上报道，如Technology Review，Laser Focus，NPR Market Place，Discovery，Popular Science和Boston Museum of Science。通过合作，PI小组开发的THz激光器通过增加一个关键的使能组件，帮助加强了其他机构在THz相关活动中的基础设施。 首席研究员已将研究项目中的元素纳入固态物理研究生课程和本科基础课程信号与系统。此外，还努力让代表性不足的少数民族成员、妇女和本科生参与研究活动。2010年，基于PI团队开发的技术，一名前学生共同创立了一家初创公司LongWave Photonics。从那时起，该公司已向全球客户销售了许多THz激光器（Easy QCL）交钥匙系统。我们完全期望拟议的工作将能够开发新的商业产品，这将是许多客户感兴趣的生化社区。这样的发展将确保美国在这一技术领域的领导地位，并在美国创造高薪就业机会。S. 技术支持：在取得突破之后，拟议的研究旨在开发基于量子级联激光器的高性能太赫兹频率梳，并展示其在太赫兹光学相干层析成像（OCT）和双梳光谱学中的应用。最近，通过巧妙的色散工程，我们已经成功地开发了跨越~500 GHz带宽的太赫兹频率梳。作为基波振荡器，这些激光梳产生的功率比其他基于非线性频率转换的太赫兹频率梳大近四个数量级。我们计划开发均匀跨越倍频程带宽（2太赫兹）与10毫瓦输出功率的太赫兹激光频率梳，并证明他们在真实的应用。为实现这一目标，我们将开展四项相互关联的任务：开发具有跨越倍频程带宽（2 THz）的平坦增益曲线的异质THz量子级联增益介质，开发具有高折射率对比度的宽带色散补偿器以补偿这样宽的带宽上的色散，通过利用内部产生的拍音来主动地强制梳状形成并执行F-2f频率稳定，并演示了太赫兹光学相干层析成像和高分辨率双梳光谱梳的应用。这一发展将对太赫兹频率的科学和技术产生重大影响，太赫兹频率在生物化学传感和光谱学、医疗和安全应用成像、天体物理学、远程大气传感和监测以及高带宽自由空间通信方面具有巨大潜力。

Title: Terahertz (THz) Laser Frequency Combs Non-Technical: Frequency combs, which can be viewed as rulers in frequency domain, have revolutionized high-precision metrology and spectroscopy, and for which half of the 2005 physics Nobel prize was awarded. At terahertz (or trillion hertz, in a nontechnical unit), many species exhibit strong and distinctive spectral fingerprints, that is, they absorb or emit strongly at several specific frequencies at THz. THz frequency combs will be the idea tool to study those species. Prior to our breakthrough development in 2014, THz frequency combs have been generated using bulky pump lasers with nonlinear generation. As such, they are very inefficient and can produce only low levels of power (~microwatts). In our recent breakthrough, we developed laser frequency combs at THz which generated much higher power levels (~5 mW). The principal investigator's work has been reported in media aimed at broad communities such as Technology Review, Laser Focus, NPR Market Place, Discovery, Popular Science, and Boston Museum of Science. Through collaborations, the THz lasers developed in the PI's group have helped to enhance infrastructures at other institutions in THz-related activities by adding a crucial enabling component. The principal investigator has incorporated elements in the research project into a graduate course in solid-state physics and a undergraduate foundational course Signals and Systems. Furthermore, effort has been made to involve members of underrepresented minorities, women, and undergraduate students in the research activities. In 2010, based on the technologies developed in the PI's group, a former student co-founded a start-up company LongWave Photonics. Since then, the company has sold many turn-key systems of THz lasers (Easy QCL) to customers worldwide. We fully expect that the proposed work will enable the development of new commercial products which will be of interest to many customers in biochemical communities. Such a development will secure the American leadership in this technical area, and create well-paid jobs in the U. S. Technical: Following the breakthrough, the proposed research seeks to develop high-performance THz frequency combs based on quantum cascade lasers, and to demonstrate their applications in THz optical coherent tomography (OCT) and dual-comb spectroscopy. Recently, by clever dispersion engineering we have successfully developed THz frequency combs spanning over a ~500 GHz bandwidth. As fundamental oscillators, these laser combs generate almost four orders of magnitude greater power than other THz frequency combs based on nonlinear frequency conversion. We plan to develop THz laser frequency combs uniformly spanning over an octave bandwidth (2 THz) with 10 mW output power, and demonstrate them in real applications. Towards this objective, we will pursue four interrelated tasks: developing heterogeneous THz quantum cascade gain media with flat gain curves spanning over an octave bandwidth (2 THz), developing broadband dispersion compensators with high index contrast to compensate the dispersion over such a broad bandwidth, achieving more robust comb operations by utilizing the internally generated beatnote to actively enforce comb formation and performing f-2f frequency stabilization, and demonstrating comb applications in THz optical coherent tomography and high-resolution dual-comb spectroscopy. This development will have a significant impact on the science and technologies in THz frequencies, which have great potentials in biochemical sensing and spectroscopy, imaging for medical and security applications, astrophysics, remote atmospheric sensing and monitoring, and high-bandwidth free-space communications.