Terahertz source frequency comb based on difference frequency generation from a mid-IR quantum cascade laser

非技术性：频率梳是一种光源，它的光谱由一系列离散的、间隔等的元素组成。自20世纪90年代被发现以来，频率梳以非凡的精度和速度彻底改变了计量学，光谱学和频率合成。然而，光谱学的应用受到了梳所能达到的波长范围的限制。在太赫兹（THz）光谱范围内，丰富的分子具有很强的光谱指纹或具有宽的吸收带，目前的梳子技术不容易获得。主要的挑战是需要多个光学元件或低温冷却，这导致了一个复杂和昂贵的来源。提出了一种开发室温下工作的芯片太赫兹频率梳源的新方法。这种易于使用和紧凑的光源将是一种使能技术，可以为更广泛的科学界轻松访问太赫兹光谱/成像。技术：提出的研究目标是演示一个室温，连续波，单片太赫兹频率梳源与亚毫瓦级输出功率。该方法是使用具有平顶增益和大二阶和三阶光学非线性的中红外量子级联激光器（QCL）用于太赫兹频率梳的腔内差频产生（DFG）。提出了一种双腔设计，使中红外泵浦源的输出具有独特的单模和多模操作组合。通过四波混频和设计的近零群速度色散，多模输出可以锁定到等间隔的梳状模式。这种空腔方案为通过DFG过程和宽带Èerenkov相位匹配方案创建太赫兹梳输出提供了完美的条件。与体积庞大且价格昂贵的锁模激光梳状源相比，所提出的太赫兹梳状源提供了一种单片解决方案，一旦开发出来，就有可能利用现有的半导体激光制造基础设施进行经济高效的大规模生产。这个项目是利用多学科方法来规避现有技术限制的一个很好的例子。固态物理、材料科学、非线性光学和激光物理都是研究计划的主要组成部分，它们都得到了NSF的普遍支持，在这种情况下，它们一起被用来将多个功能元素组合成一个单一的、紧凑的、高功率的器件。

Compact, Chip-based Terahertz Frequency CombAbstractNon-techniical: A frequency comb is a light source whose spectrum consists of a series of discrete, equally spaced elements. Since their discovery in the 1990s, frequency combs have revolutionized metrology, spectroscopy, and frequency synthesis with extraordinary precision and speed. However, spectroscopic applications are limited by the wavelength range that is accessible by the comb. The terahertz (THz) spectral range, where abundant molecules have strong spectral fingerprints or feature broad absorption bands, is not easily accessible with current comb technology. The main challenge is the need for multiple optical components or cryogenic cooling, which leads to a complicated and expensive source. A novel approach is proposed to develop a chip-based THz frequency comb source operating at room temperature. This simple to use and compact source will be an enabling technology which will allow easy access to THz spectroscopy/ imaging for the broader scientific community. Technical: The objective of the proposed research is to demonstrate a room temperature, continuous wave, monolithic THz frequency comb source with sub-milliwatt level output power. The approach is to use a mid-IR quantum cascade laser (QCL) engineered with a flat-top gain and large 2nd and 3rd order optical nonlinearities for the intracavity difference frequency generation (DFG) of a THz frequency comb. A dual-section cavity design is proposed to render the mid-infrared pump source with an output exhibiting a unique combination of single- and multi-mode operation. The multi-mode output can be locked to equally spaced comb modes via four wave mixing and an engineered near-zero group velocity dispersion. Such a cavity scheme provides the perfect conditions for creating a THz comb output via the DFG process and a broadband Èerenkov phase matching scheme. In contrast to a mode-locked laser comb source, which is bulky and expensive, the proposed THz comb source offers a monolithic solution that, once developed, has potential for cost-effective mass production using the existing semiconductor laser fabrication infrastructure. This project is an excellent example of a multidisciplinary approach used to circumvent existing technological limitations. Solid state physics, material science, nonlinear optics, and laser physics are all major components of the research plan, which are all supported generally by NSF, and are used, in this case, together to combine multiple functional elements into a single, compact, high power device.