太赫兹时域光谱计量研究

Terahertz (THz) spectroscopy techniques have wide and important applications in physics, chemistry, biology, iatrology, and material science. Accurate measurement and traceability techniques of THz spectrum are essential and necessary for ensuring THz applications. Therefore, THz spectroscopy metrology, i.e., measurement and traceability of THz spectroscopy, is urgently desired..Traditionally, it was used as a standard THz spectrum calibration method that calibration with the absorption spectrum lines of water vapor or carbon monoxide. However, this type of frequency-domain calibration technique suffers from the following problems. Firstly, traditional technique cannot realize real-time calibration or "sing-shot pulse" calibration, because a standard gas spectrum must be recorded before or after the sample spectrum measurement. Secondly, the errors generated from the repeatability of THz system are unable to be removed. The calibration accuracy cannot exceed the repeatablity of THz system. At last, the error generated from the nonlinear diaplacement of the optical delay cannot be corrected. Therefore, traditional frequency-domain calibration cannot satisfy the high accuracy demand of modern THz metrology..Based on the analysis of THz time-domain spectroscopy, the proposer put forward a novel technique, calibration of THz waveform in time-domain, for THz spectroscopy metrology. This proposed technique applies a laser interferometry. With this new calibration technique, the repeatability error of THz spectrum measurement can be removed essentially. This proposed technique can realize real-time calibration, because the calibration prodedure is accomplished during the procedure of sample test. The repeatablity error of THz system is removed by real-time calibration. With this technique, both linear error and nonlinear error of optical delay can be corrected. The research of THz spectroscopy metrology would provide an effective support to promote THz applications.

太赫兹光谱学在各科学领域具有广泛应用并发挥重要作用，太赫兹时域光谱参数的准确测量和量值校准是保证太赫兹应用可靠性和有效性的关键过程和前提基础，然而目前太赫兹计量学研究基本处于国际空白，太赫兹光谱计量已成为保障太赫兹应用中急需解决的科学问题。传统的太赫兹光谱校准采用水谱或一氧化碳的特征谱线进行频域校准，传统频域校准存在以下问题：一是无法实时校准；二是无法消除系统重复性误差；三是无法修正光学延迟非线性误差。这使太赫兹频域计量无法满足当代计量学和精度应用中的高准确度需求。.不同于传统的频域校准，申请人从时域光谱学的根本出发，提出了太赫兹时域校准的新方法，采用激光干涉技术对太赫兹时域波形标定校准。本项目开展太赫兹光谱溯源与标定校准的探索性研究，拟从根本上消除太赫兹时域光谱的测量误差，实现太赫兹光谱的准确计量，产生具有自主知识产权和独立溯源方法的高精度太赫兹计量技术，为太赫兹应用提供计量支撑保障。

太赫兹时域光谱技术在化学成分识别、生物医学成像、矿物油品检测、材料特性测量等方面具有重要应用。太赫兹时域光谱技术的应用以太赫兹光谱准确计量为基础和根据，为保障太赫兹光谱计量准确可靠，本项目开展太赫兹时域光谱计量研究。传统的太赫兹时域光谱校准是以水蒸汽或一氧化碳气体在太赫兹频段的特征吸收谱线为参考值，在频域直接对太赫兹光谱进行校准。校准后的测量重复性误差成为影响测量准确度的一个重要因素。. 为降低太赫兹时域光谱仪测量不重复性，实现太赫兹时域光谱的准确校准和精准测量，本项目提出了利用太赫兹时域回波脉冲校准太赫兹时域光谱仪的新方法，通过标定太赫兹时域波形中主脉冲和回波脉冲之间的时间延迟，实现太赫兹时域光谱测量的精确在线校准。提出的太赫兹回波在线校准技术通过校正太赫兹时域波形，实现太赫兹频域光谱的校准，从根本上解决了太赫兹时域光谱的标定校准问题。嵌入式在线校准技术实现了每次测量太赫兹波形的修正校准，解决了太赫兹时域波形测量重复性的问题。与传统太赫兹光谱校准方法相比，测量不重复性降低为1/7，总体测量不确定度降低为2/5。. 在太赫兹反射光谱计量方面，本项目提出一种自参考太赫兹反射光谱测量新方法，将样品前后表面的反射光谱分别作为参考光谱和信号光谱，通过比较样品前后表面反射光谱信息，实现了太赫兹反射光谱的精确测量。提出的自参考反射光谱测量方法仅需单次测量，不需分别测量样品光谱和参考光谱，简化了测量过程，也消除了测量时样品面和参考面相对位置差异引起的相移误差，实现了样品在太赫兹频段折射率和吸收系数的准确测量。. 本项目研制了测量光谱宽、信噪比高、重复性好、结果精准的透射式和反射式太赫兹时域光谱仪，在危险化学品测量、材料特性测试、安全检测和重大工程中获得推广应用。利用自主研制的太赫兹时域光谱仪作为测量工具，制备了一种在太赫兹波段高吸收率的材料。以该材料为吸收体研制了太赫兹辐射计，实现了太赫兹功率绝对测量。项目组代表中国参加国际首次太赫兹功率比对，取得测量不确定度国际最小的优异成绩，被誉为“太赫兹计量的重大里程碑”。