基于柱矢量光束的纵向拉曼信号探测

提出了一种获得径向偏振光中纵向分量激发拉曼信号的方法,用于解决一般偏振拉曼信号无法检测分子取向垂直于样品的问题。首先使用聚焦后的角向偏振光和径向偏振光激发样品,然后用两种激发光产生的拉曼信号进行计算,得到由纯纵向光场激发的拉曼信号。使用Si(0 0 1)样品和Si(1 1 0)样品验证了该方法的可行性。这对于使用拉曼散射信号测量纵向取向的分子,以及纵向的分子振动模式具有一定意义。     

基于光子晶体光纤参量振荡器的CARS成像光源研究

研究了一种基于光子晶体光纤参量振荡器的相干反斯托克斯拉曼散射(CARS)成像光源。该光源采用中心波长为1 030nm的皮秒光纤激光器作为泵浦源,以无截止单模光子晶体光纤作为参量增益,通过搭建光参量振荡器,实现平均功率为10mW的参量激光输出。在色散滤波效应的作用下,该光源输出波长可实现连续可调,调谐范围为782～793nm,对应的波数覆盖范围为2 901～3 078cm-1。该光源产生的两束激光脉冲可实现空间自同步、时间自重合,用于CARS成像测量时,无需空间、时间对准,有望推动CARS成像光源向全光纤化、小型化的方向发展。     

关于共振拉曼精确测量的几个问题

共振拉曼的原理及其应用已有许多报导,本文对在测量中应注意的几个问题作介绍。在共振拉曼光谱中样品的吸收和噪声是精确测量共振拉曼光谱的主要障碍。在共振拉曼实验中用与样品吸收相当的激光频率来照射。彼样品吸收的能量以三种形式来影响共振拉曼光谱,使光谱减弱。(1)入射光和     

径向偏振光瞳滤波共焦拉曼光谱显微系统研制

针对共焦拉曼系统空间分辨力提升的迫切需求,研制了一套径向偏振光瞳滤波共焦拉曼光谱显微系统(RPCRS)。该系统利用径向偏振光发生器(S波片)将激光器发出的线偏振光转换为径向偏振光;然后,利用光瞳滤波器对径向偏振光进行调制,从而压缩拉曼激发光斑;最后,利用共焦针孔消除焦点外位置的拉曼散射光,进一步提升共焦拉曼显微系统的空间分辨力。该系统具有较高的空间分辨力和横向灵敏度。以周期性刻线和标准台阶作为测试样品进行实验,实验结果表明,RPCRS的空间分辨力可以达到240 nm,横向灵敏度相比普通拉曼共焦系统提升了46.5%,测量标准不确定度为18.87 nm。该系统可用于高空间分辨共焦拉曼成像。     

长度标准器超声清洗参数设计研究

针对提高激光诱导击穿光谱技术(LIBS)中等离子体的发射光谱强度的问题,提出一种在铜样品表面沉积金纳米颗粒的方法。在样品表面沉积纳米金颗粒后对铜进行激光诱导击穿(NELIBS),得到NELIBS和LIBS下的发射光谱强度增强因子、信噪比等参数。实验表明,通过在铜样品表面沉积金纳米颗粒的LIBS(NELIBS)可以有效增强等离子体辐射光谱信号强度,铜元素谱线增强因子最高可达8.01,微量元素镁元素谱线增强因子最高为6.01,且增强因子均随激光能量的增加而逐渐减小并趋于稳定;NELIBS可以明显改善信噪比,铜元素在激光脉冲能量为80 mJ时达到最优,镁元素在激光能量为50 mJ时达到最优。对谱线Cu I 521.8 nm和Mg II 279.569 nm进行洛伦兹拟合,并得到半高全宽,发现纳米金颗粒使谱线半高全宽增加,谱线Mg II 279.569 nm的半高全宽增加了165.58%,谱线Cu I 521.8 nm的半高全宽增加了30%。样品中的微量元素因谱线强度低、信噪比差而无法探测到,通过此方法可以有效提高探测能力。     

入射激光对激光扫描共聚焦显微镜分辨率的影响

利用点扩散函数(PSF)研究了入射激光的偏振态和光束的束腰直径对激光扫描共聚焦显微镜(LSCM)分辨率的影响。根据Wolf和Richards的矢量衍射积分,建立了LSCM N-1层界面下的照明PSF模型,对零层和两层界面下的PSF进行了计算分析。结果显示:在零层界面下,圆偏振光入射的PSF在xy平面内关于焦点旋转对称,半峰全宽为0.43μm,x向线偏振光入射时PSF在x、y方向的半峰全宽分别为0.48,0.39μm;在圆偏振光入射的PSF中,高斯光束充溢系数为0,1,2,5对应的半峰全宽分别为0.43,0.47,0.62,1.49μm。在两层界面下,当探测深度为50μm时,圆偏振光PSF的半峰全宽为0.26μm,x向线偏振光入射时PSF在x、y方向的半峰全宽分别为0.28,0.24μm;在圆偏振光入射的PSF中,充溢系数为0,1,2,5对应的半峰全宽分别为0.26,0.28,0.32,0.68μm。以上计算结果表明,和线偏振光相比,圆偏振光在一个方向的分辨率优于线偏振光,在相垂直的另一个方向的分辨率弱于线偏振光,圆偏振光PSF在xy平面内关于焦点旋转对称,得到了较好的成像质量;物镜入瞳直径与激光束腰直径比值越小,LSCM的分辨率越好。     

纳米金改善激光诱导等离子体探测方法研究

针对提高激光诱导击穿光谱技术(LIBS)中等离子体的发射光谱强度的问题,提出一种在铜样品表面沉积金纳米颗粒的方法。在样品表面沉积纳米金颗粒后对铜进行激光诱导击穿(NELIBS),得到NELIBS和LIBS下的发射光谱强度增强因子、信噪比等参数。实验表明,通过在铜样品表面沉积金纳米颗粒的LIBS(NELIBS)可以有效增强等离子体辐射光谱信号强度,铜元素谱线增强因子最高可达8.01,微量元素镁元素谱线增强因子最高为6.01,且增强因子均随激光能量的增加而逐渐减小并趋于稳定;NELIBS可以明显改善信噪比,铜元素在激光脉冲能量为80 mJ时达到最优,镁元素在激光能量为50 mJ时达到最优。对谱线Cu I 521.8 nm和Mg II 279.569 nm进行洛伦兹拟合,并得到半高全宽,发现纳米金颗粒使谱线半高全宽增加,谱线Mg II 279.569 nm的半高全宽增加了165.58%,谱线Cu I 521.8 nm的半高全宽增加了30%。样品中的微量元素因谱线强度低、信噪比差而无法探测到,通过此方法可以有效提高探测能力。     

现代显微成像技术综述

概述了光学宽视场显微镜、共聚焦显微镜、超分辨率显微镜中所应用的现代显微成像技术,对各种传统和先进的显微成像原理进行了总结。光学宽视场显微镜最常用的显微技术有明场成像、暗场成像、相衬成像、偏光成像、微分干涉(DIC)成像、调制对比成像和荧光成像。相衬成像中根据不同的成像结构还有切趾相衬成像。微分干涉除了传统的偏振光照明还有圆偏振光照明(C-DIC)和专用于塑料的微分干涉(PlasDIC)。共聚焦显微镜随着计算机技术和制造技术的发展而有了巨大的发展。除了传统的共聚焦荧光显微镜以外,还有连续反斯托克斯拉曼散射(CARS)共聚焦、多光子共聚焦和白光共聚焦。超分辨率显微镜中主要介绍了受激辐射淬灭(STED)技术和紧随基态淬灭显微技术的单分子返回(GSDIM)技术。     

飞秒激光烧蚀石英玻璃表面质量分析

基于不同激光功率线烧蚀试验,研究激光偏振模式对烧蚀线宽度及表面形貌特征的影响。结合线烧蚀优化参数,开展不同线重叠率δ的面烧蚀试验,利用表面轮廓仪进行烧蚀表面粗糙度分析;建立扫描速度和线重叠率对残留高度影响的关系表达式,并进行计算分析。研究表明,当线偏振方向平行于扫描方向时,线偏振光烧蚀线质量优于圆偏振光,且其烧蚀线宽比圆偏振光大。当δ由65%增大到90%时,线偏振光烧蚀面垂直于扫描方向的轮廓算数平均偏差Ra先减小后增大,并在δ=80%时达到最小值1.05 μm;圆偏振光Ra随δ增大而减小,在δ=90%时达到最小值1.63 μm。此外,烧蚀面微观不平度十点高度Rz计算结果与试验结果基本吻合,且Rz与δ呈线性关系,并随δ增大而减小。     

新型光子纳米射流器件的设计

光子纳米射流是一种高强度,极窄的亚波长电磁场区域,它是由介电微球或微柱体的Mie散射对电磁场的聚焦作用产生的。光子纳米射流广泛应用于激光加工、纳米光刻、光学高密度存储以及超分辨率显微镜。从径向偏振光的角度出发,使用一种介电圆环结构对光束进行聚焦,由于径向偏振光在焦点区域可以产生较强的纵向场,通过优化圆环的尺寸、折射率以及与物镜焦点的相对位置,可以得到超过90%光束质量的纵向光子纳米射流,而且强度相比于未使用圆环时可以提高约一个数量级,并在高折射率下可以获得半高全宽小于衍射极限尺寸的光斑,因此该结构预计可以在粒子加速、光镊以及拉曼光谱学中有所应用。     

Application of a high power Yb fiber‐based laser compatible with commercial optical parametric oscillator for coherent anti‐stokes raman scattering microscopy

Coherent anti‐Stokes Raman scattering (CARS) microscopy is a powerful tool for chemical analysis at a subcellular level, frequently used for imaging lipid dynamics in living cells. We report a high‐power picosecond fiber‐based laser and its application for optical parametric oscillator (OPO) pumping and CARS microscopy. This fiber‐based laser has been carefully characterized. It produces 5 ps pulses with 0.8 nm spectral width at a 1,030 nm wavelength with more than 10 W of average power at 80 MHz repetition rate; these spectral and temporal properties can be slightly modified. We then study the influence of these modifications on the spectral and temporal properties of the OPO. We find that the OPO system generates a weakly spectrally chirped signal beam constituted of 3 ps pulses with 0.4 nm spectral width tunable from 790 to 930 nm optimal for CARS imaging. The frequency doubling unconverted part is composed of 7–8 ps pulses with 0.75 nm spectral width compatible with CARS imaging. We also study the influence of the fiber laser properties on the CARS signal generated by distilled water. In agreement with theory, we find that shorter temporal pulses allow higher peak powers and thus higher CARS signal, if the spectral widths are less than 10 cm^?1. We demonstrate that this source is suitable for performing CARS imaging of living cells during several hours without photodamages. We finally demonstrate CARS imaging on more complex aquatic organisms called copepods (micro‐crustaceans), on which we distinguish morphological details and lipid reserves. Microsc. Res. Tech. 77:422–430, 2014. © 2014 Wiley Periodicals, Inc.     

Investigation of microstructured chitosans by coherent anti‐Stokes Raman microscopy

This work describes application of coherent anti‐Stokes Raman scattering (CARS) microscopy technique for analytical characterization of microstructured materials based on chitosan. We demonstrate that nitrogen–hydrogen vibration band in the high wavenumber region of CARS spectrum prevails over response from oxygen–hydrogen vibrations and can be used as a spectral marker of chitosan. The chemically selective imaging is experimentally demonstrated by applying CARS microscopy to discriminate between chitosan and polystyrene microparticles. CARS microscopy was shown to be a valuable tool for characterization of polluted chitosan fibre from utilized engine filter material. A possibility to observe foreign material pieces on the surface of the polluted chitosan fibre is demonstrated and discussed.     

Small-size terahertz spectrometer using the second harmonic of a femtosecond fiber laser

Possible implementations of a small-size terahertz spectrometer with a subpicosecond resolution on the basis of a femtosecond fiber laser are considered. An experimental sample of a spectrometer is fabricated. This spectrometer employs the method of optical rectification in a ZnTe nonlinear crystal and the Dember (photodiffusion) effect on the InAs semiconductor surface to generate terahertz radiation and the polarization-optical method to detect radiation. System operation is demonstrated by an example of measuring the terahertz absorption spectrum of water and determining the refractive index of the β-BBO crystal. The basic spectrometer parameters are found: spectral range, spectral resolution, and dynamic range of the terahertz spectrum amplitude.     

A Computer-Based Laser System for the Diagnostics of Hydrogen in Gas Mixtures

A computer-based laser system for the selective diagnostics of hydrogen in gas mixtures based on the coherent anti-Stokes Raman scattering (CARS) method using biharmonic pumping on the basis of stimulated Raman scattering (SRS) is developed. The system includes a generator of single-mode and single-frequency laser radiation with one Nd³⁺:YAG active element, a frequency converter on a KTP crystal, an SRS oscillator on compressed hydrogen, measurement and reference CARS cells, and an optical and electronic system for recording the CARS signal. The system operates under the control of an IBM-compatible computer through a data input/output card based on a PCI bus. The system ensures the selective detection of hydrogen in gas mixtures at a total pressure of 1 kPa with a repetition rate of up to 10 Hz at a sensitivity of 10^–11mol/cm³, which at this pressure approximately corresponds to 20 ppm.     

一种低温极化电子拉曼散射系统简介

本文介绍了一种低温极化电子拉曼散射系统的组成、结构、用法及成果。拉曼散射是一种常见的非弹性光散射现象。通过检测散射光谱,可以对材料的内在基础性质进行深入研究。拉曼散射光中也包含了更深层次的电子激发信息,表现为连续的拉曼谱,并具有很低的信号强度,需要严格控制杂散光的影响,并需低温（液氦）和高真空的极端条件。为此,我们设计并建造了一套低温极化（低温下光的偏振）电子拉曼散射系统,并获得一些科研成果。     

Novel diode-pumped infrared tunable laser system for multi-photon microscopy

We report on a novel laser source, emitting high energy (20 nanoJoule) femtosecond pulses, in a broad spectrum (250 nm). This source is easily tuned from 950 to 1200 nm, without any laser adjustment, and delivers sub-300 femtosecond pulses with a 10-nm spectral width.     

用于激光频率参数测量的飞秒光学频率梳

近年来随着光纤制造技术和飞秒激光技术的成熟,以掺铒(Er)光纤光学频率梳为代表的频率梳技术,逐步突破了光学 频率测量领域,在长度测量、精密光谱分析、超低相位噪声微波频率产生、精密时间频率传递、温度测量等领域发挥出越来越重 要的作用,已成为许多高端科研领域的基础性工具。 但飞秒光学频率梳所解决的重要问题是对激光频率进行测量。 本文主要 面向激光频率参数测量的需求,研制基于掺 Er 光纤飞秒激光器的光学频率梳,在实现光学频率梳稳定运转的前提下,通过非线 性光学频率变换技术,实现光谱范围从掺 Er 光纤光学频率梳的中心波长向各个待测激光波长的转换,并完成与多个不同波长 激光的拍频信号探测。 目前已验证的飞秒光梳可测频率范围为 500 ~ 2 000 nm;频率稳定度和准确度为 10 -16 量级;线宽为 Hz 量级。 该指标满足了激光频率特性参数测量的需求,为激光绝对频率、频率漂移、线宽等参数的测量提供了基础性的测量工具。     

Computer-Controlled Liquid Chromatographic System that Includes a UV-Visible Scanning Spectrophotometer and a Coherent Anti-Stokes Raman Spectrometer

ABSTRACT

Resonance enhanced coherent anti-Stokes Raman spectrometry (CARS) has been demonstrated as a specific identification system for liquid chromatography. To achieve this work in the areas of CARS. liquid chromatographic preconcentration and separation, and computer control of the liquid chromatograph/ultraviolet-visible/CARS experiments were undertaken. Column selection, flow rate, and solvent composition were monitored and controlled. The ultraviolet-visible spectrometer was used at a fixed wavelength until a species was detected. The flow was stopped, the absorption spectrum was scanned, and flow was resumed. After calculation of the optimum excitation frequency, the Raman spectrum was scanned under control of the computer with on-line signal averaging and data smoothing.