宽谱太赫兹量子级联激光器频梳色散研究

The frequency comb consists of a series of equally spaced frequency lines with ultrahigh frequency stability and ultralow phase noises. Frequency combs operating in visible and near-infrared wavelengths have been already used in various applications, such as high resolution spectroscopy, absolute frequency measurement, laser-based distance measurement, and so on. However, in the terahertz (THz) frequency range, due to the lack of high efficiency and broadband THz radiation sources, the research on terahertz frequency comb is still in its infancy. The THz quantum cascade lasers (QCL), capable of high power emission, low far-field divergence angle, wide frequency coverage (1.2-5 THz), is regarded as an ideal candidate for generating frequency combs in THz frequency regime. The project is aiming to study the basic group velocity dispersion in broadband THzQCLs theoretically and experimentally, and finally demonstrate THzQCL frequency combs. The main research contents are listed as follows: 1) overcome the narrow gain property in QCLs, design broadband THzQCL structures based on multiple-stack active regions. 2) investigate the dispersion in broadband THzQCLs and demonstrate the solutions for achieving dispersion compensation in THzQCLs. 3) by employing the dispersion compensation mechanisms, achieve broadband THzQCL frequency comb. The results of the project could pave the way for the THz nonlinear pump-probe and high resolution spectroscopy using the dual-comb technique.

频梳是由一系列频率稳定性高、相位噪声低的等间距频率线组成。可见光和近红外光频梳已经应用于高分辨成谱、绝对频率测量、激光测距等领域。然而，在太赫兹（THz）波段，由于缺乏高效、宽谱THz辐射源，THz频梳的研究还处于初级阶段。THz量子级联激光器（QCL）具有高功率输出、低远场发散角、宽频率覆盖范围（1.2-5 THz）等特性，被认为是研究实用化THz频梳最理想的载体。本项目旨在基于课题组已经研制的高性能THzQCL器件，从理论和实验两方面研究宽谱THzQCL最基本的群速度色散物理问题，最终实现宽谱THzQCL频梳。具体研究内容包括：1）克服QCL增益窄的关键物理问题，设计多有源区堆叠宽谱THzQCL结构；2）理论和实验研究宽谱THzQCL的色散并提出色散补偿方法；3）利用色散补偿机制，在实验上实现宽谱THzQCL频梳。本项目的研究成果预期在THz泵浦探测和高分辨成谱中起到关键奠基作用。

半导体太赫兹（THz）量子级联激光器（QCL）具有电泵浦、大功率、低阈值、高质量远场光斑等优势，是产生THz光频梳的理想载体。实现THzQCL光频梳的内在机制是非线性四波混频效应。而THzQCL群速度色散分析是实现四波混频锁模的重要物理基础。本项目系统研究了THzQCL群速度色散，取得了以下成果：（1）完成2-5 THz频率范围内THzQCL光频梳的色散计算，针对双面金属波导和半绝缘等离子波导THzQCL结构进行了色散评估，并提出色散补偿方案；（2）基于非线性饱和吸收和色散补偿，实现了高稳定THzQCL被动光频梳，重复频率线宽低至700 Hz；（3）基于高稳定THzQCL光频梳，实现了宽带THzQCL双光梳。项目执行期内发表论文25篇，授权中国发明专利12项。项目负责人及团队成员获得国家基金委“优青”、当选上海市优秀学术带头人、上海市青年拔尖人才、国家“博新”计划等。