Collaborative Research: Quantum cascade laser sources of high-power, coherent frequency combs

摘要：非技术性：该项目的目标是在中红外光谱范围内开发紧凑、实用、高功率的相干频率梳半导体激光源。这些梳子就像频率空间中的尺子一样，可以快速准确地读取分子振动的频率。这些频率可以作为不同分子的唯一标识符。因此，所提出的激光源将实现超宽带和快速分子光谱，在痕量气体环境监测、药品质量控制和生化试剂远程检测等方面具有广泛的应用。该项目将探索一种新的频率梳产生机制，该机制基于量子级联激光器中的相干脉冲。该项目将由哈佛大学和德克萨斯农工大学的团队成员共同努力，并与来自欧洲的世界领先的光谱专家合作。这将为所有相关的学生和研究人员创造独特的跨学科和多文化的教育、研究和推广机会。技术：本合作研究的目标是在连续泵浦量子级联激光器的基础上开发中红外相干频率梳的高功率半导体激光源。在过去的三年里，量子级联激光锁模和频率梳领域得到了迅速的发展，这要归功于提出建议的团队和其他几个团队的贡献。然而，到目前为止，宽带相参梳已经在特殊设计的激光器中在接近阈值的窄电流范围内得到了证明。超快增益松弛是大多数模式锁定技术的根本障碍。提出建议的团队将专注于通过相干拉比振荡获得频率梳的新途径，这将导致以太赫兹频率间隔分隔的模式的相位相干“超级梳”的参数化产生。由此产生的谐波锁模在时域上相当于太赫兹频率下的幅度调制，与增益弛豫率相当。这种新的频率梳产生机制是完全相参的，本质上工作在足够高的阈值以上，每个模式产生高功率。该项目将采用几种策略，利用Rabi机制，使用标准高性能激光芯片产生稳定、高功率和宽带梳子。

Abstract title: Compact, high-power semiconductor laser sources of coherent frequency combs for fast and efficient molecular detectionAbstract:Non-technical: The objective of the project is the development of compact, practical, high-power semiconductor laser sources of coherent frequency combs in the mid-infrared spectral range. The combs work as rulers in frequency space, providing fast and accurate readings of frequencies of molecular vibrations. These frequencies can serve as unique identifiers of different molecules. Therefore, the proposed laser sources will enable ultra-broadband and fast molecular spectroscopy, which has a wide range of applications in trace gas environmental monitoring, pharmaceutical quality control and remote detection of biochemical agents. The project will explore a new mechanism of frequency comb generation, which is based on coherent pulsations in quantum cascade lasers. The project will be pursued as a collaborative effort between the team members at Harvard and Texas A&M University and in collaboration with world-leading spectroscopy experts from Europe. This will create unique inter-disciplinary and multi-cultural education, research, and outreach opportunities for all involved students and researchers. Technical: The objective of this collaborative research is to develop high-power semiconductor laser sources of coherent frequency combs in the mid-infrared based on continuously pumped quantum cascade lasers. The field of quantum cascade laser mode locking and frequency combs has seen rapid expansion over the last three years, due to contributions of the proposing team and several other groups. However, so far broadband phase-coherent combs have been demonstrated in lasers of special design in a narrow interval of currents near threshold. Ultrafast gain relaxation presents a fundamental obstacle to most mode locking techniques. The proposing team will focus on a new route to frequency combs through coherent Rabi oscillations, which result in parametric generation of a phase-coherent "supercomb" of modes separated by terahertz frequency intervals. The resulting harmonic mode locking is equivalent in time domain to amplitude modulation at terahertz frequencies comparable to the gain relaxation rate. This new mechanism of frequency comb generation is entirely phase-coherent and intrinsically operates high enough above threshold, yielding high power per mode. The project will pursue several strategies of utilizing the Rabi mechanism for generation of stable, high-power, and broadband combs using standard high-performance laser chips.