Ⅰ型准相位匹配周期性极化铌酸锂倍频蓝光输出

在周期为14．5μm的周期性极化铌酸锂中,利用d31得到了一阶Ⅰ型EY^ωEY^ω-Ez^2ω(oo-e)准相位匹配蓝光二次谐波。在150C下,由114μJ抽运光,得到了52μJ,0．473μm倍频蓝光,对应于平均最大转换效率45．6%。制备了一阶和三阶周期分别为4．5μm和13．5μm的周期性极化铌酸锂。在EY^ωEY^ω-Ez^2ω(ee-e)准相位匹配0．473μm蓝光倍频中。150C下,分别得到了41．3%和19%的倍频转换效率。oo-e准相位匹配比传统的ee-e准相位匹配有较大的光栅周期,尤其在短波长区域倍频输出应用中,降低了周期性结构制作的困难,其较大的容许带宽在实验中提高了频率转换效率。实验结果表明了在周期性极化铌酸锂中准相位匹配倍频的偏振相关性。     

一阶准相位匹配周期性极化铌酸锂倍频产生18 mW绿光连续输出

通过高压脉冲电场极化 ,制备了周期为 6 5 μm、长为 12mm、宽为 10mm、厚为 0 5mm的一阶准相位匹配周期性极化铌酸锂 ;由 1 1W连续 1 0 6 μmNd∶YAG激光器抽运 ,在 5°时产生了约 18mW、0 .5 32 μm的倍频连续绿光 ,其对应的二次谐波转换效率约为 1 6 % ,二次谐波的归一化转换效率约为 1 5 %cm- 1 W- 1 ,相当于 79%的周期性极化铌酸锂的理想非线性系数。测量了抽运光功率与倍频光功率的关系     

准相位匹配周期极化高掺镁铌酸锂532 nm倍频准连续输出研究

对周期性极化高掺镁铌酸锂倍频过程进行了准相位匹配倍频理论研究。在室温下通过外加电场极化法,用较低的极化开关电场～5．5kV／mm,在厚为1mm、长为10mm、宽为10mm的掺镁铌酸锂基片上成功地制备了周期为5．8～7．3pm(间隔0．3pm)的一阶准相位匹配倍频周期性极化光学微结构。将温度控制在70℃左右,以波长为1．060μm的Nd：YAG激光为基频光源,对所研制的光学微结构样品进行倍频通光实验验证。当入射基频光为920mW时,可以获得约15mW的532nm准连续倍频蓝光输出．其归一化转换效率高达1．77％／W。     

准相位匹配PPLN倍频理论研究与优化设计

对准相位匹配周期性极化铌酸锂(PPLN)倍频进行了理论研究，并对聚焦高斯光束条件下的倍频耦合波方程进行了求解，给出了准相位匹配倍频转换效率公式，分析了晶体长度与聚焦程度的关系，在此基础上对倍频谐振腔进行了优化设计，以期获得最大的倍频转换效率.本结果对准相位匹配倍频器件的设计具有一定的指导意义. 关键词： 倍频 准相位匹配 周期性极化铌酸锂     

宽带准连续光纤激光在周期极化铌酸锂中倍频特性的研究

双包层光纤激光器和非线性光学材料(如周期性极化的铌酸锂晶体,PPLN)相结合,开辟了实用性非线性光学器件的一个新领域。研究了准相位匹配周期性极化反转铌酸锂晶体对宽带准连续光纤激光倍频的温度特性和频谱特性。在理论上,从准相位匹配相位失配关系出发,推导了晶体温度与抽运源中心波长的关系以及温度响应带宽,并和已报道实验结果进行了比较,二者符合得很好。此外,还推导了倍频周期极化铌酸锂晶体对抽运基频光源的响应谱线带宽。在实验上,采用长度20mm,极化周期6．5μm,厚度0．5mm的周期极化铌酸锂晶体光纤激光器准连续宽带输出进行了倍频,获得了在不同控制温度下的倍频光光谱,并对此进行了详细分析。     

可调谐准相位匹配高效宽带二次谐波转换

高效宽带二次谐波转换在光通信、信号处理和光谱学等很多领域都有重要的应用.通常高效宽带二次谐波转换的研究都集中在几个波长,为了得到可调谐准相位匹配高效宽带二次谐波转换,理论分析了准相位匹配和群速度匹配条件.在此基础上,分别计算了0型和Ⅰ型准相位匹配情况下,温度对5 mol%掺杂氧化镁周期性极化铌酸锂和周期性极化铌酸锂晶体准相位匹配高效宽带二次谐波转换的影响.对于5 mol%掺杂氧化镁周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度15 nm和341 nm的可调谐准相位匹配高效宽带二次谐波转换;对于周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度44 nm和98 nm的可调谐准相位匹配高效宽带二次谐波转换.拓展了准相位匹配高效宽带二次谐波转换的波长范围.     

准相位匹配倍频系统的带宽性质研究

根据准相位匹配倍频原理,讨论了实现宽带二次谐波转换需要满足的条件.以周期性极化铌酸锂晶体和掺杂氧化镁（7mol%）周期性极化铌酸锂（7mol%MgO-PPLN）晶体为例,分别比较了0型（e+e→e）和Ⅰ型（o+o→e）两种准相位匹配情况下宽带高效二次谐波转换的特性.研究表明,对于7mol%MgO-PPLN晶体,同时满足准相位匹配条件和群速度匹配条件的中心波长和带宽向短波方向移动,且0型（e+e→e）准相位匹配情况下可以获得更大的带宽.     

半导体激光直接倍频的488nm蓝光激光器

利用波导型准相位匹配周期极化反转铌酸锂(PPLN)晶体直接倍频波长为976 nm的连续半导体激光二极管,在最佳晶体工作温度(28℃)下,获得了波长为488 nm的连续蓝光输出,最大输出功率大于20 mW。所用的晶体尺寸为8 mm×1.4 mm×1 mm,波导截面为4.5μm×3.5μm,极化周期为5.2μm。研究了波导型周期极化反转铌酸锂晶体的倍频效率与温度的关系,与普通的周期极化反转铌酸锂相比,倍频效率与温度关系的敏感度较低。同时,由于晶体可以在室温下工作,简化了加温与温控部件,提高了整机的工作效率。在此实验的基础上,制成了一台小型的全固态488 nm连续蓝光激光器。     

准相位匹配扇形光栅铌酸锂光波导倍频绿光输出

采用外加电场极化方式对具有扇形光栅的 0 .5mm厚Z切铌酸锂晶体进行极化反转 ,制成了退火质子交换光波导。极化反转周期为 5 .8μm～ 6 .2 μm ,采用Nd∶YAG激光器输出的 1.0 6 4 μm连续激光为基频光波 ,实现了0 .5 32 μm倍频绿光输出 ,相互作用长度为 4mm ,耦入波导的基频光波功率为 10mW ,获得了 2 0 μW的绿色倍频光输出 ,归一化转换效率为 12 5 % (W·cm2 )。     

准相位匹配周期极化掺镁铌酸锂490 nm倍频连续输出

在室温下通过外加电场极化法,首次用较低的极化开关电场～5.5 kV/mm,在厚为1 mm、长为20 mm、宽为18 mm的掺镁铌酸锂基片上成功的制备了周期为4.8～5.2 μm的一阶准相位匹配倍频光学微结构;并在室温下,以波长为980 nm的半导体激光器为基频光源,对所研制的微结构样品进行倍频通光实验,在入射基频光为800 mW时,产生约40 mW的490 nm的倍频光,其对应转换效率为5%,实验过程中未见绿致吸收光折变现象.     

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.     

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.     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

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.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.