Spectral Beam Combining of Fiber Lasers by Using Reflecting Volume Bragg Gratings

By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser beam is near-diffraction-limited with a beam factor M^2-1.54. During this 4-channel beam-combining process, no special active cooling measures are used to evaluate the volume Bragg gratings as combining elements are under the higher power laser operation. Thermal expansion and period distortion are verified in a 2 k W 2-channel beam-combining process, and the heat issue in the transmission case is found to be more remarkable than that in the diffraction e-se. Transmitted and diffracted beams experience wave-front aberrations with different degrees, thus leading to distinct beam deterioration.

Spectral redshift of high-order harmonics by adding a weak pulse in the falling part of the trapezoidal laser pulse

We investigate the spectral redshift of high-order harmonics of the H_2~＋（D_2~＋） molecule by numerically solving the non-Born–Oppenheimer time-dependent Schr ¨odinger equation（TDSE）. The results show that the spectral redshift of highorder harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H_2~＋ molecule, the shift of high-order harmonic generation（HHG） spectrum for the D_2~＋ molecule is more obvious.We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.

Spectral and laser properties of Yb and Ho co-doped(YLa)_2O_3 transparent ceramic

Highly transparent Yb,Ho doped（YLa）2O3 ceramic was fabricated by conventional ceramic processing with nanopowders.The absorption and emission spectra of the ceramic was investigated.The energy transfer mechanism between Yb3＋ and Ho3＋ was also discussed.The strong emission band around 2 μm indicated that the Yb-Ho：（Y 0.90 La 0.10）2O3 transparent ceramic is a promising gain medium for the generation of 2 μm laser emissions.The laser operation of Yb-Ho co-doped（YLa）2O3 ceramic at 2.1 μm is first reported.

Spectral Enhancement of Laser-Induced Breakdown Spectroscopy in External Magnetic Field

In this paper the spectral enhancement of laser-induced breakdown spectroscopy （LIBS） for copper plasma in the presence of a magnetic field is investigated and the temporal- and spatial-resolved plasma emission spectra are analyzed. Experimental results show that the copper plasma atomic and ion spectra have been enhanced in the presence of the external magnetic field. In addition, the Cu I 521.82 nm spectral intensity evolution with delay time appears to have a double peak around the delay time of 2 μs, but that of Cu II 507.57 nm has a sharp decrease because of the electron-atom three body recombination process. The plasma temperature with magnetic confinement is lower than that of the case in the absence of magnetic fields. Finally, the spectral enhancement mechanisms of laser induced breakdown spectroscopy with magnetic confinement are analyzed.

Comparison of ultrasound biomicroscopy and spectraldomain anterior segment optical coherence tomography in evaluation of anterior segment after laser peripheral iridotomy

AIM：To quantitatively assess narrow anterior chamber angle using spectral-domain anterior segment optical coherence tomography（SD-AS-OCT） and ultrasound biomicroscopy（UBM）,and to evaluate the correlations and consistency between SD-AS-OCT and UBM.· METHODS：Fifty-five eyes from 40 patients were examined.Patients were diagnosed with primary angleclosure glaucoma（PACG） remission（11 eyes from 8patients）,primary angle closure（PAC,20 eyes from 20patients） and PAC suspect（24 eyes from 12 patients）.Each eye was examined by SD-AS-OCT and UBM after laser peripheral iridotomy（LPI）.The measurements of SD-AS-OCT were angle open distance（AOD）,anterior chamber angle（ACA）,trabecular iris angle（TIA）,and trabecular iris space area（TISA）.UBM measurements were AOD and TIA.Correlations of AOD500 and TIA500 between UBM and AS-OCT were assessed.All parameters were analysed by SPSS 16.0 and MedCalc.· RESULTS：ACA,TIA and AOD measured by SD-ASOCT reached a maximum at the temporal quadrant and minimum at the nasal quadrant.Group parameters of AOD500 and AOD750 showed a linear positive correlation,and AOD750 had less variability.UBM outcomes of AOD500 and TIA500 were significantly smaller than those of SD-AS-OCT.The results of the two techniques were correlated at the superior,nasal and inferior quadrants.CONCLUSION：Both UBM and SD-AS-OCT are efficient tools for follow-up during the course of PACG.We recommended using parameters at 750 μm anterior to the sclera spur for the screening and follow-up of PACG and PAC.The two methods might be alternatives to each other.

Nd∶GdYAG激光晶体的光谱分析及热学性能研究

本文对所生长的Nd∶GdYAG晶体的吸收光谱和荧光光谱进行了测试,采用Judd-Ofelt理论对振子强度和线强、强度参数Ω_(t)、4 F_(3/2)→4 I_(J)能级间的跃迁概率、能级辐射寿命、荧光分支比等光谱参数进行了计算,相关数据与YAG、LuAG、YVO4等晶体进行了对比。Ωt计算得出Ω2=(0.813±0.200)×10^(-20)cm^(2),Ω4=(3.381±0.187)×10^(-20)cm^(2),Ω6=(5.135±0.278)×10^(-20)cm^(2),相比YAG、LuAG、YVO4等晶体,Nd∶GdYAG晶体的强度参数Ω2较大,表明Gd^(3+)的掺入增大了基质的无序度。计算并拟合了300~1200 nm的吸收截面和折射率,其中808 nm处的吸收截面为5.0×10^(-20)cm^(2),1064 nm处的折射率为1.80。实测4 F3/2能级的荧光寿命为228μs,与计算的能级辐射寿命240μs接近;1064 nm处的发射截面为1.23×10^(-19)cm^(2),接近Nd∶YAG晶体的发射截面。室温下Nd∶GdYAG晶体的热导率为5.992 W/(m·K),略小于Nd∶YAG和Nd∶GGG,但大于Nd∶YVO4晶体。研究表明,Nd∶GdYAG是一种有应用前景的新型激光晶体材料。

基于5 kHz平面激光诱导荧光的射流火焰局部熄火时空特性分析

基于高频光学测量手段研究射流火焰局部熄火的分布特性,对于分析燃烧场不稳定性机理有重要意义。建立5 kHz的平面激光诱导荧光测量系统,对高速射流火焰开展实验研究,并获得火焰结构的动态发展过程;将双边滤波、竖直滑窗局部自适应阈值等图像处理方法引入平面激光诱导荧光图像的预处理,在局部断裂结构数量特征的基础上,提取局部断裂结构长度和空间位置等特征;基于上述特征深入解析局部熄火的时空分布特性,进一步完善高频平面激光诱导荧光诊断与分析方法。研究表明:双边滤波算法处理后,图像峰值信噪比为34.3 dB,结构相似度为0.93,噪声水平显著降低,获得了较好的去噪效果;使用竖直滑窗局部自适应方法进行图像分割的F1分数达到93.30%;断裂结构累计数量随时间线性增加,当射流马赫数由0.5增至1.6时,单侧图像断裂结构的每秒累计数量从790.7增至9 217.2,并且局部熄火频率与射流马赫数呈指数关系;断裂结构主要分布区域为火焰臂及上侧中央燃料区。本研究进一步拓展了高频平面激光诱导荧光技术的应用能力,证明了高频平面激光诱导荧光技术用于局部熄火时空分布特性研究的可行性。

基于光谱合束的双波长输出Nd:YAG固体激光器

报道了一种基于光谱合束的Nd:YAG固体激光器双波长光源。系统由两个固体Nd:YAG脉冲激光器通过光谱合束组合而成,两个固体Nd:YAG脉冲激光器可独立工作,有利于输出脉冲的波长调谐、功率调节和相对延迟调整。通过光栅的色散特性以及输出镜的共同外腔反馈将各个激光器锁定在不同波长,从而实现合束,获得的激光源中心波长锁定在1 061.5 nm和1 064.6 nm,两谱线中心间距为3.1 nm,组合光束的输出能量为173 mJ,组合光束的光束质量因子M2为2.8×2.2;两个Nd:YAG激光器独立工作的输出能量分别为94 mJ和92 mJ,在合束方向上的光束质量因子M2分别为2.7和2.1,在非合束方向上的光束质量因子M2分别为2.2和1.9;组合光束的输出能量为两个Nd:YAG激光器能量总和的93%,组合光束的光束质量因子与单个Nd:YAG激光束的光束质量因子M2基本相同。该双波长激光源满足波长间隔小、输出功率大小相近、同光轴等要求,在太赫兹波产生、测速激光雷达以及医疗仪器等应用领域具有重要作用。

SuperCam-LIBS光谱定量分析火星锰元素

毅力号火星车携带的SuperCam载荷可以探测火星表面锰元素等成分信息。本研究依据SuperCam团队发布的地质标样激光诱导击穿光谱(LIBS)数据集,提出了一种基于集成学习的火星锰元素定量方法。本研究首先对LIBS光谱进行光谱降噪、去基线等预处理,随后进行光谱反卷积和分峰拟合,最终建立锰元素的定量方法,实现了锰元素的含量预测。实验评估了传统多变量定量方法(LASSO、弹性网络)和集成学习方法对锰元素定量精度的差异,发现后者的均方根误差相对于前两种传统方法分别平均下降了49%和30%,定量结果更接近样品真实值,表明基于集成学习的定量方法更适用于火星锰元素的定量反演。

基于光谱增强技术实现对532 nm波长激光频率标定

碘稳频532 nm Nd:YAG激光器在复现长度单位“米(m)”、绝对重力测量、引力波探测、精密光谱学、长度计量等领域有着重要应用,对其进行频率测量和标定对于激光器的性能评价具有重要意义.本文采用自行研制的掺Er光纤光学频率梳作为光源,对其扩谱后的1μm波段进行光谱增强并结合倍频晶体将光学频率梳输出的1.5μm波段光脉冲扩展到532 nm波段.其中掺Er光纤光学频率梳输出功率20 mW,首先经过掺Er光纤放大器将功率提到370 mW,经过脉冲压缩后脉冲宽度为45.7 fs,此后经过高非线性光纤扩谱实现光谱覆盖至1μm,输出功率为180 mW.扩谱后的1μm波段激光经过掺Yb光纤放大器放大至601 mW,经过压缩后脉冲宽度为84.6 fs,压缩后功率为420 mW.采用MgO:PPLN晶体对压缩后激光进行倍频得到155 mW的532 nm激光,倍频效率为36%.利用该系统分别对碘稳频532 nm Nd:YAG激光器输出的基频光1064 nm和倍频光532 nm进行拍频,获得了优于40 dB信噪比的拍频信号,后续进行了超过10 h的连续测量,测量结果与国际推荐值保持一致.

锌的激光诱导击穿光谱与等离子体温度研究

金属锌的探测工作对于诸多领域有着重要意义。本研究采用激光诱导击穿光谱技术对锌进行了检测分析,标记出锌在200~895 nm波段内的31条特征谱线。并且在不同激光能量下进行了多次探测,发现激光能量对于锌谱线的相对强度影响显著。同时计算了不同激光能量下的等离子体温度,发现等离子体温度随着激光能量的增加而逐渐升高。此外,研究了离子线与原子线强度比和等离子体温度的关系,结果表明,锌的离子线与原子线强度比和等离子体温度之间呈正相关趋势。

飞秒激光直写光纤光栅进展及光谱优化方法研究

光纤光栅传统的制备方法为紫外曝光法和CO_(2)激光法。紫外曝光法具有操作简单,容易对准等优势,但通常需要对光纤进行载氢增敏处理且高温下折射率调制容易被擦除,难以在极端环境下实现应用价值。CO_(2)激光法通常用于长周期光纤光栅的制备,测量灵敏度容易受到高温的影响。针对传统光纤光栅制备方法存在的问题,飞秒激光刻写技术随之出现,大致被分为飞秒激光直写法、飞秒激光全息干涉法和飞秒激光相位掩模法。其中,飞秒激光直写法具备刻写效率高、脉冲能量要求低等特点,还能根据传感需求调制中心波长、光栅间距、光栅长度等。此外,飞秒激光直写法的实验装置简单,不需要相位掩膜板控制光栅周期。飞秒激光直写的光纤光栅具有折射率调制灵活、高温性能好、机械强度高等优点,已在传感器、激光器等多种光学器件中广泛应用。文章简要介绍飞秒激光直写光纤光栅的工作原理及典型写制方法,总结了飞秒激光逐点、逐线、逐面三种直写方法的国内外研究进展;从制备效率、光谱质量等方面对比分析了三种直写方法的优缺点;详细分析和讨论了光谱优化方法,包括激光脉冲能量、光栅长度、光纤类型、光束整形和光栅切趾,为获得高反射峰、窄3 dB带宽、低插入损耗的高质量光纤光栅奠定基础。最后展望了飞秒激光直写光纤光栅的发展趋势和应用前景。

考虑云团衰减作用的激光制导炮弹弹道规划

针对多云天气条件下,云团对激光信号产生较大衰减作用从而影响末制导性能这一问题,提出一种考虑云团对激光衰减作用的滑翔增程激光制导炮弹弹道规划方法。经过合理假设建立云团近似模型,在此基础上设计云团规避—控制能量最优复合规避目标函数(Compound Evasion Objective Function,CEOF)。根据激光导引头工作特性和制导炮弹的飞行特性建立弹道规划模型,采用Radau伪谱法将弹道规划问题转化为非线性规划问题(Non-linear Programming,NLP)。调用NLP求解器SNOPT求解。选取多组云团算例进行仿真分析,仿真结果验证所提弹道规划方法的有效性。研究结果表明,与传统弹道规划方法进行仿真对比,新的弹道规划方法以增加较少动能损耗、控制能量消耗和攻击时长为代价,大幅减少了云团对激光的衰减作用,验证了其优越性。

激光诱导击穿光谱技术在光谱数据的增强和定量分析上的基础研究

激光诱导击穿光谱技术(Laser-Induced Breakdown Spectroscopy, LIBS)是一种通过脉冲激光聚焦样品产生等离子体,对等离子体发射光谱进行分析进而得到物质成分和含量的一种原子发射光谱技术。LIBS由于其成本低、适用范围广、样品无需复杂的预处理、检测速度快且可实现原位检测等特点成为了元素分析的一大热门,在工业、环境保护、生物医学、珍贵物品鉴定、军事等领域都有着很好的应用前景。但在分析元素种类与含量时,对光谱结果的分析常会受到基体效应、自吸收效应、等离子体屏蔽效应等因素的影响,使得提高LIBS技术的精确度成为了一大议题。本文基于LIBS的简介和基本原理和技术优点,详细分析了LIBS现阶段存在的问题及光谱增强的途径,并综述了定量分析的指标和方法,为LIBS更精确的检测提供了更多途径。

用于离轴积分腔输出光谱的非对称拟合算法设计

目的:研究离轴积分腔光谱技术(OA-ICOS)在实际应用中快速的激光扫描造成吸收谱线非对称,而传统的线型拟合函数无法满足,导致拟合误差大,测量精度低的问题。方法:介绍了一种基于OA-ICOS的非对称拟合算法用于拟合非对称吸收谱线,提升测量精度。该算法从OA-ICOS的原理出发分析导致谱线非对称的原因,并结合Voigt线型函数引入非对称特征,获得含非对称因子的谱线拟合函数。结果:在实验中,分别设置激光扫描频率为50 Hz、150 Hz、300 Hz时,利用Voigt拟合算法得到的吸收峰中心位置偏移量分别为4×10^(-3) cm^(-1)、4.8×10^(-3) cm^(-1)、6.2×10^(-3) cm^(-1),使用非对称拟合算法得到的吸收峰位置偏移仅分别为2.4×10^(-3) cm^(-1)、2.4×10^(-3) cm^(-1)、1.5×10^(-3) cm^(-1)左右。结论:在快速激光扫描频率下,该算法能够更准确地拟合非对称吸收光谱信号,从而提高了拟合精度。

Spectral and Lasing Properties of Er^(3+0/Yb^(3+) Co-Doped Phosphate Glasses Pumped by LD

Er^3 ＋/Yb^3 ＋ phosphate glasses were fabricated. According to McCumber theory, the stimulated emission cross-section of Er^3＋ ions at 1533 nm was calculated on the basis of absorption spectrum, and 0.84 × 10^-20 cm^2 is derived, the fluorescence lifetime of ^4I13/2 level is 8.5 ms. An Er^3＋/Yb^3＋ co-doped phosphate glass CW laser pumped by LD was demonstrated at room temperature. The maximum output power is 80 mW and slope efficiency is 16.5%.

Helicity of harmonic generation and attosecond polarization with bichromatic circularly polarized laser fields

We theoretically investigate the high-order harmonic generation(HHG) of helium atom driven by bichromatic counterrotating circularly polarized laser fields. By changing the intensity ratio of the two driving laser fields, the spectral chirality of the HHG can be controlled. As the intensity ratio increases, the spectral chirality will change from positive-to negativevalue around a large intensity ratio of the two driving fields when the total laser intensity keeps unchanged. However, the sign of the spectral chirality can be changed from positive to negative around a small intensity ratio of the two driving fields when the total laser intensity changes. At this time, we can effectively control the helicity of the harmonic spectrum and the polarization of the resulting attosecond pulses by adjusting the intensity ratio of the two driving laser fields. As the intensity ratio and the total intensity of the driving laser fields increase, the relative intensity of either the left-circularly or right-circularly polarized harmonic can be enhanced. The attosecond pulses can evolve from being elliptical to near linear correspondingly.

Investigation on Structures and Properties of Yb^(3+)-Doped Laser Glasses

The Yb3^＋ -doped silicate, phosphate and borophosphate laser glasses were prepared by means of conventional melt quenching technology. The physical and spectral properties of the glasses were investigated. The results show that, due to the existence of OH^-, the fluorescence lifetime of phosphate glass is shorter than that of silicate glass, so silicate glass has better spectral properties than phosphate glass. Silicate glass has better mechanical and thermal properties than phosphate glass, but with the addition of B2O3, mechanical and thermal properties of phosphate glass are improved greatly without fluorescence quenching effect. This kind of borophosphate glass can be used in high average power solid state lasers.

Experimental investigation of laser-produced-plasma EUV source based on liquid target

A laser-produced plasma(LPP) source was built using liquid as target and a Nd:YAG laser as the irradiation laser, and the LPP source's radiation with ethanol and acetone target respectively was measured by an AXUV100 silicon photodiode combined with a McPHERSON model 247 grazing incidence monochromator of the resolution Δλ≤0.075 nm and the wavelength scanning interval 0.5 nm. Both ethanol and acetone target LPP source had EUV emission at 11～20 nm wavelength. The comparison between the spectra of the two kinds of target materials shows that all the two kinds of target source's spectra are the result of oxygen ions' transitions under current source's parameters, but the spectrum intensity from different target sources is different. The spectra intensity from the ethanol target is higher than that from the acetone target. In addition, the target liquid is forced into the vacuum chamber by the background pressure supported by the connected external high pressure gas, and the influence of the background pressure on the source's intensity is investigated.

宽光谱多参数激光告警探测研究

随着激光技术的发展,激光武器得到了快速发展,针对来袭激光的威胁,激光告警也成为目前各国发展的重点,不同的激光告警系统探测不同的参数,根据告警参数采取相应的躲避和反击措施;目前激光告警主要探测参数有来袭激光方位角、俯仰角、激光波长、激光脉冲宽度等,但现有激光告警系统无法实现多参数的同时探测,且光谱范围窄、视场小、探测俯仰角和方位角为相对角度、无法获得绝对来袭方向。为此本文提出宽光谱波段、大视场、多参数激光告警新方法,可实现450~1700 nm宽光谱来袭激光波长、绝对方位角、绝对俯仰角、脉冲宽度多参数的高精度综合测量,该方法主要由激光脉冲宽度测量、绝对角度及激光波长测量、控制及数据处理三大部分组成。其中脉冲宽度测量模块由光学镜头、多带通窄带滤光片、高速光电探测器组成,实现来袭脉冲激光的高速光电转换;绝对角度及激光波长测量模块由光栅、大视场宽波段消色差镜头、多带通窄带滤光片、宽波段面阵探测器、三维电子罗盘组成,通过一级和零级衍射光斑位置获得来袭激光波长、相对方位角和相对俯仰角信息,结合三维电子罗盘测得的方位角、俯仰角以及横滚角,进而获得来袭激光的三维绝对方位角和绝对俯仰角。多带通窄带滤光片主要是根据常用几个军用激光波长进行选通滤光,有效滤除背景光的影响,降低系统虚警、漏警。理论分析推导具体测量方法和参数,设计宽光谱多参数激光告警探测系统样机,并进行实验可行性验证。实验结果表明,该系统的方位角视场120°、俯仰角视场96°、角度测量精度优于1°、中心波长测量精度优于10 nm、脉宽测量精度优于3 ns。该技术将为海、陆、空、天领域对来袭激光的高精度多参数综合探测奠定基础,有望提高复杂战场的生存能力。