用于核物理研究的精密激光谱技术的发展和展望

原子核基本性质（自旋、质量、寿命、磁矩、电四极矩和电荷半径等）与原子核的内在结构密切相关,是检验和发展原子核理论模型的重要依据。实验上可以通过多学科交叉的精密激光谱技术测量原子核外电子的超精细结构和同位素移位,来模型独立地提取原子核的自旋、磁矩、电四极矩和电荷均方根半径等多个核物理参量。这些基本性质的系统测量可以用于探索不稳定原子核中展现出来的新奇的物理现象与规律。近年来,为了测量产额更低的丰中子核的基本性质,激光谱技术不断更新和发展,以实现高分辨、高效率测量。本文详细介绍了激光谱测量的基本原理以及由此发展起来的用于不稳定原子核结构研究的各类互补的激光谱学技术,如共线激光谱（高分辨率低灵敏度）、在源激光谱（高灵敏度低分辨率）、共线共振电离谱（高分辨率高灵敏度）等激光谱技术,以及在不同核区的测量优势和局限。最后结合我国正在发展和规划中的新一代放射性核束装置,讨论精密激光谱技术在国内的发展以及在核物理研究中的应用。     

Einstein Lecture – Passion for precision

Optical frequency combs from mode‐locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective.     

A Review of Signal Enhancement and Noise Reduction Techniques for Tunable Diode Laser Absorption Spectroscopy

Abstract: Tunable diode laser absorption spectroscopy (TDLAS), as a noninvasive spectroscopic method, permits high-resolution, high-sensitivity, fast, in situ absorption measurements of atomic and molecular species and narrow spectral features in gaseous, solid, and liquid phases. Advances in new diode laser sources and laser spectroscopic techniques generally have triggered an increasing application of TDLAS in various disciplines (for example, atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics and combustion monitoring, etc.) over the last four decades. This article reviews some important developments in TDLAS, from its basic principles as a spectroscopic tool to the demonstration of gas absorption measurements, emphasizing signal enhancement and noise reduction techniques developed for improving current TDLAS performance.     

太赫兹光谱和成像技术在食品安全检测中的应用

随着超快激光技术的快速发展以及人们对太赫兹辐射与物质作用机理的进一步认识,太赫兹辐射作为一项新的、快速发展的技术在很多领域受到广泛关注,在安全检测、医学诊断、无线通信和制药等诸多领域预示着广泛的应用前景。由于食品安全问题的重要性,食品安全的检测技术面临着巨大的机遇与挑战。太赫兹光谱与成像技术提供了一种新型的食品安全检测手段。相比于其他技术,THz技术具有高信噪比和动态范围宽等诸多特点, 能够同时获得样品在THz波段的时域信息与频域信息,以及对应的物质物理结构和化学成分等重要信息,在食品安全检测领域具有独特的优势。文章简要介绍了太赫兹波的概念、特点和技术手段,太赫兹辐射技术在食品安全领域的最新应用进展,并讨论了THz技术应用的限制因素, 展望了THz技术的应用前景。     

可调谐激光吸收光谱法与气相色谱法监测甲烷的对比研究

甲烷是一种重要的温室气体,它对大气中温室效应的贡献仅次于二氧化碳.针对环境空气中甲烷的测定,从测量原理、测量过程和测量装置等方面比较了可调谐二极管激光吸收光谱和气相色谱法两种测量方法.结果表明用上述两种方法测得的甲烷的日变化趋势具有良好的一致性.相比较而言,后者造价更低,并且更方便.     

Laser engineering of spine discs

The laser engineering of intervertebral discs is one of the branch of medical physics aimed at the development of minimally invasive laser medical techniques based on the effect of the controlled (time- and space-modulated) laser radiation on the structure and the field of mechanical stress of biological tissues. A new method for the laser engineering of the intervertebral discs and the differences of this approach from the existing physical methods of medical treatment are considered. The newly formed tissues of animals and humans are hystologically studied. Possible regeneration processes are discussed. A control system that provides for the treatment efficiency and safety is developed. The new laser medical equipment that is designed for the laser engineering of intervertebral discs is described, and the corresponding results of the clinical application are presented.     

Spectral and modulation properties of a largely tunable MEMS-VCSEL in view of gas phase spectroscopy applications

An extensive characterization of the spectral properties of a largely tunable laser in the 1.56-μm spectral range is reported. This device combines a vertical-cavity surface-emitting laser (VCSEL) with a micro-machined (MEMS) Bragg mirror in a very compact arrangement. The large tunability obtained by an electro-thermal actuation of the MEMS mirror makes this device very attractive for high-resolution spectroscopy. Relevant laser parameters for the implementation of wavelength modulation spectroscopy techniques in gas sensing, such as tuning and modulation properties, are presented. A preliminary gas spectroscopy experiment performed with this laser is also shown.     

Solid-state laser sources for (anti)hydrogen spectroscopy

Conclusion Recently developed high-power semiconductor laser amplifiers offer new ways to construct laser sources for high-resolution spectroscopy in the blue and ultraviolet. Such sources overcome a number of limitations that are connected to the standard single-mode ring laser systems. A source of this kind can contribute significantly to the feasibility of antihydrogen spectroscopy. Experiments with hydrogen will also benefit greatly. The construction of an optical hydrogen frequency standard becomes realistic and experiments with demanding atomic preparation techniques as, for instance, optical cooling in magnetic traps are facilitated.     

Exploration of gold nanoparticle beams for matter wave interferometry

We investigate molecular beam methods for gold nanoparticles. They are based on electrospray, matrix assisted laser desorption and thermal laser desorption in combination with mass spectroscopy and multi-photon ionization. These techniques are analyzed with respect to their potential for coherent matter wave experiments.     

鼻咽癌光谱诊断系统中的荧光光谱信号处理

利用激光诱导荧光技术开发了用于早期鼻咽癌诊断的自体荧光光谱系统系统由风冷氩离子激光器、自行研制的单色仪和高灵敏度、智能化的信号采集和处理系统组成文中重点讨论了系统中自体荧光光谱信号的处理技术,其中包括荧光光谱信号的分光和检测技术,以及用LabVIEW开发的信号处理和控制平台荧光光谱信号的处理结果表明:系统不仅实现了荧光光谱信号的同步显示,而且极大地提高了信号的信噪比,这为系统的临床应用奠定了的基础.     

Nonlinear optical techniques for plasma diagnostics

The application of various nonlinear optical laser spectroscopic techniques to plasma diagnostics are reported. The techniques discussed in this paper are two-photon laser induced fluorescence spectroscopy, double-resonant four-wave mixing, coherent anti-Stokes Raman-scattering (CARS), and a combination of emission spectroscopy and CARS. They are applied to measurements of atomic hydrogen densities, molecular temperature, chemical composition, electric field distributions, and vibrational population distribution. The basic principles are described and important aspects of the methods are discussed in context with application to various kinds of discharges at low and elevated pressures     

Laser spectroscopy : 1. Principal problems

Laser spectroscopy has made it possible to solve, or at least to begin solving, a number of important problems to which classical spectroscopy could not be applied. These problems are defined in this, the first in a series of articles reviewing the subject of laser spectroscopy. This is followed by an outline of the present status of tunable lasers — the basic instruments used in developing the techniques of laser spectroscopy.     

Several applications of laser diagnostics for visualization of combustion phenomena

Several applications of laser diagnostic techniques to visualize combustion phenomena are presented, including reactive Mie scattering for flow, Rayleigh and Raman spectroscopy for major species, laser-induced fluorescence for minor species, and laser extinction, scattering, and laser-induced incandescence for soot. These techniques have been applied to diffusion flame oscillation, a recirculation zone in a burner, laminar and turbulent lifted flames, flame propagation along a vortex tube, and soot zone characteristics, to demonstrate the usefulness of the techniques to provide a better understanding of physical mechanisms.     

Laser induced breakdown spectroscopy for multielement analysis of powdered materials used in additive technologies

Additive manufacturing technologies utilizing metal parts production with layer by layer printing are of high demand for different fields of science and technology. Analytical chemistry is challenged to provide multielemental quantitative analysis of any metal powders within a few minutes and onsite to fulfil the requirements for high quality metal parts production. Powder materials utilized in additive technologies were quantitatively analyzed by laser induced breakdown spectroscopy for the first time. Laser induced breakdown spectroscopy mapping of loose metal powder attached to the double-sided adhesive tape provided high reproducibility of measurements even for powder mixtures with large difference of particles densities (tungsten carbide particles in nickel alloy powder). Laser induced breakdown spectroscopy analytical capabilities were estimated for tungsten and carbon analysis by calibration curve construction and accuracy estimation by leave-one-out cross-validation procedure. Laser induced breakdown spectroscopy and X-ray fluorescence spectroscopy techniques comparison revealed better results for laser induced breakdown spectroscopy analysis. Improved accuracy of analysis and capability to quantify light elements (carbon, etc.) demonstrated the potential of laser induced breakdown spectroscopy as a promising technique for express onsite multielement analysis of powder materials utilized in additive technologies.     

中红外波段大气碳同位素激光吸收光谱研究

大气碳同位素在环境污染源汇示踪和地球化学发展等方面的应用越来越广泛,在其探测技术方面,激光吸收光谱技术具有体积小、可在线、灵敏度高等优点,在气体同位素探测中越来越受到重视。工作中研究了2.7 μm波段的分布式反馈激光器(distributed feedback laser, DFB)可调谐半导体激光器的性能,在遵循12CO₂和13CO₂同位素分子吸收谱线特征和同位素分子谱线选择原则的基础上,确定了合适的激光器输出波长。结合光程390.3 m的新型多次反射池,实现了大气中CO₂分子的δ13C同位素丰度探测。     

连续和准连续激光调制谱分析技术的比对研究

为了在面对不同检测需求时,能够选取适合的调谐激光吸收光谱技术方案,对直接吸收光谱、连续调制谱和准连续调制谱三种方法进行了理论分析和实验比较。在相同实验条件下,通过同一激光器测量不同浓度CO2气体,比较了这三种方法的技术特点、信号特征、检测灵敏度。结果表明,准连续调制谱技术具有与连续调制谱相当的检测灵敏度,但是受激光能量间断和较大的寄生幅度调制影响,检测信号相对于气体吸收谱的线形失真较大,因此不太适合依赖光谱线形和线宽的压力、流速测量。为选取更加适用的激光调制谱技术,提供了参考依据。     

Spectroscopic and X-ray diffraction study of high Tc epitaxial YBCO thin films obtained by pulsed laser deposition

We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO₃ by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films.     

稀土原子与离子的自然辐射寿命测量

概述了当前自由原子和离子的激发态自然辐射寿命测量技术的进展。以LaⅠ和PrⅡ为例,系统介绍了几种稀土元素自由原子和离子激发态寿命测量技术并分析了它们的优缺点;以SmⅡ为例,详细介绍了激光烧蚀产生自由原子(离子)技术及结合激光诱导荧光时间分辨光谱技术进行激发态寿命测量的优缺点。最后,探讨了改进上述技术局限性的解决思路,以期进一步提高辐射寿命测量的精确度。     

光学技术在运动人体科学中的应用

研究了光学技术在人体运动研究中潜在应用．光生物调节作用可以抑制细胞凋亡．色光疗法、低强度激光针灸和鼻腔内低强度激光照射可以调节植物神经功能和昼夜节律，它们具有防治运动性疲劳的潜在价值．蛋白质分子构型变化可以用园二色谱表征，组织和大脑血氧饱和度的变化可以用近红外光谱表征，尿液可以用傅里叶红外光谱进行代谢组学研究，它们都可以作为运动训练的有效表征工具．