Terahertz quantum-cascade vertical external cavity surface emitting lasers

本研究解决了在2-5太赫兹范围内制造具有高功率和优异光束质量的太赫兹半导体激光源的挑战。紧凑的太赫兹辐射源，具有高输出功率（数十至数百毫瓦或更高）和优异的光束质量，是一系列光谱学和成像应用的迫切需要，例如在天体物理学、大气科学、生物和医学科学、安全筛查和非法材料检测以及非破坏性评估等领域。其智力优势在于开发了一种新型的太赫兹量子级联（QC）激光器：一种垂直外腔表面发射激光器（THz QC- vecsel）。这种新方法解决了太赫兹qc激光器的一个具有挑战性的问题：如何在高功率和优秀的光束模式下运行。这种激光器的使能技术是一种所谓的“有源超表面反射器”，它由一组稀疏的天线耦合太赫兹qc激光子腔组成，这些子腔锁定在外部腔模式上。每个子腔都被设计成一个高效的散热器，并且具有非常有利的散热几何形状，从而允许高功率连续波操作。本研究将整合和统一天线工程和激光工程的互补概念。更广泛的影响涉及几个层面，包括本科生和研究生的研究经验，成果的传播和技术进步。向代表性不足的少数族裔（URM）伸出援手的具体做法是，通过PI为一门专门为招收和保留URM工科新生而设计的课程制定研究项目。其智力优势在于开发了一种新型的太赫兹量子级联（QC）激光器：一种垂直外腔表面发射激光器（THz QC- vecsel）。使能元件是一种创新的太赫兹有源超表面反射器，它由天线耦合的稀疏阵列太赫兹qc激光子腔组成。超表面反射器构成了激光腔的一部分，使得许多太赫兹qc激光子腔被锁定到高质量的因子腔模式，从而允许可扩展的功率组合。激光材料在超表面上的稀疏分布降低了平均功率耗散密度，并为热提取提供了有利的几何形状，从而使大有效面积发射器具有优异的连续波性能。主要目标是实现定向光束（单横模发散角6度）的太赫兹qc激光器，具有接近衍射限制的光束质量，脉冲模式下具有1w峰值功率的可扩展功率，连续波模式下具有200mw功率。第二个目标是设计基于工程非均匀超表面的外部太赫兹激光腔，具有定制的增益，光谱，相位和偏振响应，用于新的功能，如波束整形，波前工程和动态偏振调制。综合理论、计算和实验的努力，提出(a)设计和实现低损耗和高效放大反射QC超表面，(b)设计和实现单模操作的外腔配置，具有优异的光束质量，(c)设计和生长适用于QC- vecsel的高效量子级联活性区域材料，(d)进行热设计和工程

This research addresses the challenge of making terahertz semiconductor laser sources with high power and excellent beam quality in the 2-5 THz range. Compact sources of terahertz radiation that operate with both high output power (tens to hundreds of milliwatts or more) and excellent beam quality are sorely needed for a range of spectroscopy and imaging applications for example in the fields of astrophysics, atmospheric science, biological and medical sciences, security screening and illicit material detection, and non-destructive evaluation. The intellectual merit lies in the development of a new type of terahertz quantum-cascade (QC) laser: a vertical-external-cavity-surface-emitting-laser (THz QC-VECSEL). This new approach addresses a challenging issue for THz QC-lasers: how to operate both with high power and an excellent beam pattern. The enabling technology for this proposed laser is a so-called "active metasurface reflector", which is composed of a sparse array of antenna-coupled THz QC-laser sub-cavities locked to an external cavity mode. Each sub-cavity is designed to be an efficient radiator and have a very favorable geometry for heat removal, which allows high-power continuous-wave operation. This research will integrate and unite complementary concepts from antenna engineering and laser engineering. The broader impacts are addressed at several levels including undergraduate and graduate research experiences, dissemination of results, and technology advancement. Outreach to underrepresented minorities (URM) will specifically occur through the PI's development of research projects for a course designed for the recruitment and retention of URM engineering freshmen. The intellectual merit lies in the development of a new type of terahertz quantum-cascade (QC) laser: a vertical-external-cavity-surface-emitting-laser (THz QC-VECSEL). The enabling component is an innovative THz active metasurface reflector, which is composed of a sparse array of antenna-coupled THz QC-laser sub-cavities. The metasurface reflector forms part of the laser cavity such that many THz QC-laser sub-cavities are locked to a high-quality factor cavity mode, allowing for scalable power combining. The sparse distribution of laser material on the metasurface reduces the average power dissipation density and offers a favorable geometry for heat extraction which in turn will allow excellent continuous-wave performance of large effective area emitters. The primary goal is to achieve THz QC-lasers with directive beams (single transverse mode with divergence angle 6 degrees), with near-diffraction limited beam quality, that have scalable power of 1 W peak power in pulsed mode, and 200 mW power in continuous-wave mode. A secondary goal is the design of external THz laser cavities based upon engineered inhomogeneous metasurfaces with customized gain, spectral, phase, and polarization response for new capabilities such as beam shaping, wavefront engineering, and dynamic polarization modulation. An integrated theoretical, computational, and experimental effort is proposed to (a) design and implement low-loss and efficient amplifying reflective QC metasurfaces, (b) design and implement external cavity configurations for single-mode operation with excellent beam-quality, and (c) design and grow high-efficiency quantum-cascade active region material suitable for use in the QC-VECSEL, (d) perform thermal design and engineering