激光二极管端面泵浦Yb:YAG圆棒热效应研究

基于激光二极管端面泵浦Yb∶YAG棒工作特点的分析,提出了端面绝热、周边恒温的激光晶体热分析模型,采用了一种新的热传导方程求解方法,得到了超高斯光束端面泵浦Yb∶YAG棒温度场的一般解析表达式。同时分析了不同阶次、不同光斑半径、不同功率超高斯光束以及晶体参数改变时对于Yb∶YAG棒温度场分布的影响。研究结果表明,若准直聚焦到Yb∶YAG棒泵浦面42.5W的光束具有4阶超高斯强度分布时,掺Yb3+质量分数为10.0at.%、长度为2.5mm、半径为2mm的Yb∶YAG棒的泵浦面获得74.20℃的最高温升。新的热传导方程求解方法在研究激光棒温度场分布方面具有计算量小、精度高等特点。研究结果对减小激光晶体的热效应,提高全固态Yb∶YAG激光器性能提供了理论依据。     

激光二极管抽运（Tm，Ho）：YLF微片激光器的实验研究

从理论上分析了准三能级(Tm，Ho)：YLF晶体的增益与温度关系，晶体温度的降低和长度的缩短有利于减小重吸收损耗对激光器运行性能的影响。在室温条件下，用2．7w波长为792nm激光二极管端面抽运Tm(原子数分数0．06)，Ho(原子数分数0．004．)：YLF微片激光器，阈值抽运功率为450W，当入射到晶体内的激光二极管功率为1．88W时，2μm激光最大输出功率为328mW，斜率效率为22．5％，光—光转换效率达17．4％。为达到激光最佳运行条件，还探讨了激光二极管波长，抽运光偏振方向以及晶体温度对Tm，Ho激光器性能的影响。     

LD端面抽运Nd:YAG 1319nm/1338nm双波长激光器研究

从LD端面抽运固体激光器的激光阈值公式出发，建立了双波长激光同时振荡的阈值条件，理论计算了腔镜对于两个波长的透过率关系，实现了LD端面抽运Nd:YAG 1319nm/1338nm双波长激光连续和准连续输出.双波长激光连续输出功率可达6W，斜效率为30%；准连续输出功率在重复频率50kHz时可达4.75W，斜效率为24.73%，脉冲宽度为55.05ns；腔内插入布儒斯特片，在重复频率为50kHz时，双波长激光准连续线偏振输出功率可达2.22W，不稳定性小于0.52%，M²     

空气导热作用下Nd:YAG晶体温场特性

为了实现激光二极管端面泵浦Nd:YAG晶体温度场的精确计算,在晶体端面导热边界条件下建立热模型。首先根据热传导方程,以解析分析理论为基础,应用常数变易法和特征函数法,在考虑晶体端面存在热交换情况下,计算得到808 nm激光泵浦Nd:YAG圆棒晶体的温度场分布,分析了泵浦激光功率、光束半径及超高阶次等因素对晶体温度场分布的影响。分析结果表明:当功率为60 W、光斑半径为0. 4 mm的泵浦光作用于半径为1. 5 mm,长度为5 mm的Nd:YAG圆棒晶体时,该晶体内部最高温升出现在泵浦端面中心处,最高温升为426. 3 K,得到晶体的热透镜焦距为272. 98 mm。由于在计算中考虑了空气的导热作用对晶体温度场分布的影响,更符合实际情况,因此结果能更真实反映晶体内部温度场的分布情况。本文研究为精确分析相关激光晶体的温度场分布提供了指导,并为激光器性能的优化提供了理论依据。     

激光、激光技术 激光工作物质

TN244 2006064930 LD端抽运下几种激光晶体的端面形变研究=Study on end deformation of several LD end-pumped crystals[刊,中]/杨永明(西安电子科技大学技术物理学院．陕西,西安(710071)),周荣…//激光技术．—2006．30(1)．—73-75研究了LD端抽运下Nd：YVO_4．Nd：GdVO_4,Nd：KGW晶体的端面形变,结果表明,随着致热抽运功率的增大,端面形变热透镜焦距越来越短,均在10m以内变化．而在聚焦半径为0．45mm、光纤耦合15W时,晶体形变量在10μm以内。图4参6(严寒)     

LD泵浦Nd∶LuVO4/Cr4+∶YAG被动调Q激光器

采用大功率半导体激光器端面泵浦Nd∶LuVO4晶体，利用Cr4+∶YAG晶体作为可饱和吸收元件，实现了1.06 μm激光的被动调Q运转.在泵浦功率为19.1 W时，获得最高平均输出功率为4.58 W，脉冲宽度为84 ns，单脉冲能量为36.6 μJ以及峰值功率为436.2 W的激光脉冲.     

LD双端端面泵浦的高功率连续单频Nd:YVO4激光器

研制了高功率连续单频Nd：YVO4激光器。在考虑激光晶体因吸收泵浦光而产生的热透镜效应的基础上，设计了六镜环行激光谐振腔，采用两个光纤耦合输出的高功率激光二极管双端端面泵浦结构，在总泵浦功率为32．3W的情况下，得到10．4W的单频1．064μm红外输出，斜效率为43．7％，长期功率稳走性优于1％(4h)，激光器自由运转时的频率漂移小于150MHz（1min)。     

LD端面泵浦折叠腔Nd：YVO4／LBO激光器

对端面泵浦Nd：YVO4构成的四镜Z型折叠腔结构进行了理论研究，合理调整谐振腔的参量关系，使谐振腔能够适应不同泵浦功率下激光晶体热焦距的变化，同时所设计的折叠腔还具有腔参量调整灵活等特点，以LBO晶体为倍频晶体，采用Ⅰ类角度调节位相匹配技术，在双端泵浦光功率为26W时，成功地获得了4W稳定的连续绿光输出，Nd：YVO4／LBO绿光激光器输出为4W时的稳定性为1．3％，其光—光转换效率达到13％。     

用ZCTC晶体倍频半导体激光的紫光输出

报道了新型金属络合物非线性光学材料ZCTC（硫氰硫锌镉）晶体的光学性质。测量了ZCTC晶体的折射率,计算了其相位匹配角度。进行了半导体激光（LD）室温下直接倍频实验。当808nm基频GaAlAs半导体激光功率为473mW时,获得了390μW、4040μnm紫光输出。实验表明ZCTC晶体是一种优良的半导体激光倍频紫外非线性光学材料。     

激光二极管端面纵向泵浦Nd:YVO_4激光器的热效应研究

针对激光二极管端面纵向泵浦Nd:YVO4激光器,本文理论和实验详细研究了Nd:YVO4晶体的热透镜效应。在激光二极管的中心波长分别为808nm和880nm及分别采用单端端面纵向泵浦和双端端面纵向泵浦结构情况下,实验测量了Nd:YVO4晶体的热透镜焦距,实验结果和理论预测基本吻合。同时在泵浦功率60W时获得了18.8W的连续基横模激光输出。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.