铌酸锂晶体中飞秒激光脉冲线性电光效应及其色散补偿

针对铌酸锂晶体中飞秒激光脉冲线性电光效应, 研究了光学相位共轭 对群速度色散 以及一阶和二阶折射率色散的补偿方案. 结果发现, 在任意初始输入脉宽条件下, 这些色散基本上都能得到补偿, 输出脉冲波形基本上和输入脉冲相同. 在此方案中, 若同时在色散补偿铌酸锂晶体上对输出脉冲进行电光相位调制, 则在一定外加电场作用下, 输出脉冲的脉宽将进一步被压缩, 初始输入脉宽越小, 压缩程度越大.     

基于铌酸锂双折射晶体的皮秒拍瓦激光系统光谱整形

为补偿皮秒拍瓦激光系统中钕玻璃宽带放大引起的增益窄化,提出了一种基于铌酸锂双折射晶体的高能量光谱整形方法.在相同强度调制下,对比了BBO、铌酸锂和石英3种晶体,针对1053 nm激光,选用了高双折射率、大口径且不易潮解的铌酸锂作为整形晶体.理论分析了晶体厚度、倾斜角、面内旋转角对强度调制的影响,发现它们分别决定调制的带宽、中心波长及深度.并对整形过程中晶体引入的光谱相位进行了分析,发现各阶色散量随晶体厚度、倾斜角、面内旋转角变化的规律,因此可通过上述参数控制各阶色散量.在此基础上,开展了中心波长为1053 nm、带宽为10 nm、调制深度为80%的光谱整形实验和相位测量实验,实验与理论分析相一致.针对神光Ⅱ皮秒拍瓦激光系统,利用上述整形方案,国内首次实现了1700 J, 6 nm (FWHM)的高能宽带激光输出,有效补偿了增益窄化.研究结果对国内基于钕玻璃放大系统的宽频带激光装置的工程研制具有重要意义.     

周期性极化铌酸锂晶体的电光复合逻辑门

根据准相位匹配线性电光效应耦合波理论,基于单个周期性极化铌酸锂晶体,提出了外电场可控的电光复合与门、或门的逻辑计算方法.采用级联周期性极化铌酸锂晶体,探讨了外电场可控的电光复合逻辑异或门、半加法器、半减法器的逻辑计算方法.在外加电场分别为0.184KV/mm和0.368KV/mm条件下,分析了光波的波长、方位角和极角、晶体的温度对逻辑输出的影响.研究结果表明,基本逻辑门的逻辑计算能够成功实现,但其逻辑计算对光波波长、晶体温度、方位角和极化角非常敏感,这些参量轻微的变化会导致逻辑输出的改变.该方案可推广到更为复杂的基本逻辑门以及三个以上逻辑输入与输出的基本逻辑门中.     

紫外超短脉冲激光放大过程中脉宽压缩的方案设计

采用放电泵浦KrF准分子激光放大器放大波长为248.4nm的紫外超短脉冲激光。对于能量为0.7mJ、脉宽为550fs的输入脉冲,在光束直径保持10mm不变的条件下,能量放大到15mJ,脉宽展宽到1200fs。为了压缩输出脉冲宽度,分析了群速度色散和自相位调制效应对脉宽展宽的影响。利用棱镜对,采用4种不同的实验方案对脉冲引入负的线性频率啁啾,以补偿KrF准分子激光放大器CaF2窗镜中的群速度色散和自相位调制对脉冲引入的正的线性频率啁啾。结果表明:在放大器之前放置棱镜对的方式可以在保持输出脉冲能量为15mJ的同时,在棱镜对间距为110cm的条件下,将输出脉冲宽度压缩到370fs,输出波长为248.4nm、带宽为0.4nm。     

基于单块周期极化铌酸锂晶体级联三倍频的440 nm蓝光固体激光器

阐述了一种基于单块周期极化铌酸锂晶体级联三倍频实现440 nm蓝光输出的实验方案。根据周期极化铌酸锂晶体的Sellmeier方程以及倍频与和频的相位匹配条件,在一块周期极化铌酸锂晶体上设计了两段不同的极化周期,使其在同一工作温度下能分别实现倍频与和频,在先后经过倍频与和频后,实现级联三倍频输出。实验采用Nd: YAG产生的1319 nm光作为基频光,重频400 Hz,脉宽110 ns,横向和纵向光束质量因子分别为1.81和2.65。耦合进周期极化铌酸锂晶体后,出射光中检测到660 nm的红光和440 nm的蓝光。通过调整工作温度和入射基频光功率,得到2.4 mW的最大蓝光输出,此时工作温度55.5 ℃,基频光功率530 mW。实验结果验证了单块晶体实现级联三倍频440 nm蓝光输出的可行性。     

棱镜对色散补偿系统的时域ABCD矩阵分析方法

讨论了棱镜对的负色散效应,利用时域ABCD矩阵方法分析了高斯型光脉冲经棱镜对色散补偿系统的脉宽和啁啾的变化,指出输出光脉冲的脉宽是展宽还是压缩,与棱镜啁啾、棱镜间距和光脉冲在棱镜中传输的距离的取值有关.讨论了棱镜对色散补偿系统对脉冲压缩的最佳条件,指出此时输出光脉冲脉宽随棱镜啁啾的增大而骤减,且骤减程度随啁啾增大而逐渐削弱,最后趋于一稳定值.     

基于晶体劈的电光晶体半波电压测量

通过测量外加电压下电光晶体的相位延迟来获取半波电压.基于双折射晶体劈的偏光干涉法,将通过电光晶体后的偏振光相位延迟量转化为干涉条纹的平移,通过定位暗纹位置进行精密的线性测量.实验结果表明:偏光干涉法测量铌酸锂晶体相位延迟的测量准确度为4.4×10-3 rad,所测量铌酸锂晶体的半波电压为480.0V,其测量误差为0.10%,远小于极值法0.96%的测量误差.偏光干涉法光路结构简单、测量准确度高、测量结果不受光功率波动的影响,且电光晶体相位延迟量的测量范围不受限制.     

铌酸锂光学电场传感器温度稳定性改善研究

铌酸锂晶体材料具有较高的电光系数和稳定的物理、化学性质,广泛应用在各种电场传感器中。但是,铌酸锂晶体折射率对温度较为敏感,在使用最大电光效应方向时,由于自然双折射的存在,晶体工作点随温度漂移,一方面导致传感器无法稳定工作,另一方面也影响了传感器的灵敏度和动态范围。为了消除这一影响,探头中将使用长度相等、主轴正交的两块铌酸锂晶体,一块作为传感晶体,一块作为补偿晶体。由于补偿晶体的存在,传感器的自然双折射得到很大程度的抑制,温度稳定性也得到了改善。经实验对比,补偿之后的传感器工作状态稳定性比未补偿的传感器得到大幅提升。     

正色散克尔介质中光脉冲的传输

综合考虑了在２＋１维正色散介质中克尔效应衍射、色散对光脉冲传输的影响，得到了脉宽、束宽传输的一般规律，并以高斯光束为例用数值法近似讨论了耦合强度、初始脉宽、初始啁啾对自聚焦及自相位调制自脉宽压缩的影响。     

正色散克尔介质右光脉冲的传输

综合考虑了在２＋１维正色散介质中克尔效应衍射，色散对光脉冲传输的影响，得到了脉宽，束宽传输的一般规律，并以高斯光束为例用数值法近似讨论了耦合强度，初始脉宽，初始啁啾对自聚焦及自相位调制自脉宽压缩的影响。     

Wave-coupling theory of linear electro-optic effect for ultrashort laser pulses

A wave-coupling theory of linear electro-optic (EO) effect for ultrashort laser pulses has been developed. As one of its applications, the linear EO effect of ultrashort Gaussian pulses propagating in LiNbO₃ crystal is demonstrated, with the intensity lower than the damage threshold. It is found that the EO effect is sensitive to both the azimuth angle and the polar angle of wave vector of light. And the larger the applied electric field, the shorter the crystal used for optimization of EO coupling is. The numerical results show that, with the duration of input pulse changing from 150 fs to 5 fs, the durations of output pulses are broadened due to the group-velocity dispersion, as well as the first- and second-order refractive dispersion. In addition, when input pulse duration is larger than 20 fs, in contrast with zero chirp, the output durations can be slightly compressed if a positive chirp input pulse is used. The validities of slowly varying amplitude approximation and continuous wave approximation are also discussed. The influence of self-phase modulation and cross-phase modulation on the EO effect is also discussed briefly.     

高强度飞秒激光脉冲在空气中的自压缩

利用高重复频率（1kHz）、吉瓦级飞秒激光脉冲实验验证了高强度飞秒脉冲在空气中的自 压缩现象，研究了入射脉冲在不同初始啁啾情况下经空气中聚焦成丝后，时域及频域特性随 入射脉冲能量的变化规律.实验结果表明，在无需后继色散补偿情况下，高强度飞秒脉冲仅 通过在空气中的非线性传输过程就可以实现脉冲压缩；在入射脉冲为负啁啾情况下，实验观 察到脉冲光谱及时域宽度同时得到压缩，并可获得比激光源所能提供的更短的近双曲正割型 变换限脉冲. 关键词： 高强度飞秒激光脉冲 自压缩 自聚焦     

Non-critically phase-matched,Ti:Sapphire-pumped picosecond optical parametric oscillator using LiB3O5

We report a new source of high-repetition rate and widely tunable picosecond pulses for the near infrared. A singly resonant, cw, picosecond optical parametric oscillator based on temperature-tuned LiB₃O₅ and synchronously pumped by 1.8 ps pulses from a self-mode-locked Ti:Sapphire laser is demonstrated. The oscillator can provide average output powers of up to 90 mW under non-critical type-I phase matching at a pulse repetition rate of 81 MHz. Without dispersion compensation, transform-limited signal pulses with 720 fs durations have been generated at 1.2 times threshold. With the available mirror set, signal tuning over 1.374–1.530 µm and idler tuning over 1.676–1.828 µm is demonstrated for a range of pump wavelengths and phase-matching temperatures. With additional mirrors, continuous tuning throughout 1–2.7 µm should be readily attainable with a single LiB₃O₅ crystal.     

Optimizing input and output chirps up to the third-order for sub-nanojoule,ultra-short pulse compression in small core area PCF

Compression of sub-nanojoule laser pulses using a commercially available photonic crystal fiber (PCF) with zero dispersion wavelength of 860 nm is discussed. A twofold pulse compression starting from 24 fs transform limited seed pulses around 800 nm is experimentally demonstrated as a verification of our simulations. Theory shows that by the optimization of input and output chirp parameters up to the third order, high quality, 5.7 fs pulses can be generated from a cost efficient experimental setup. Further calculations show that 1 ps pulses with central wavelength of 800 nm can be compressed down to 50 fs in the normal dispersion regime of the fiber with proper dispersion compensation. Calculations also show that dispersion flattened fibers can improve both the quality and the duration of compressed pulses. PACS 42.65.Re     

Passive picosecond and femtosecond mode-locking laser action of Yb<Superscript>3+</Superscript>:LuYSiO<Subscript>5</Subscript>

Efficient passive mode locking of a diode-pumped Yb³⁺:LuYSiO₅ (Yb:LYSO) laser is first demonstrated in experiment using a semiconductor saturable absorber mirror (SESAM), to the best of our knowledge. A stable pulse train with a repetition rate of 101 MHz is generated. The average output power of 2.13 W and the pulse duration of 3.9 ps. With a pair of SF10 uncoated prisms for dispersion compensation, we obtained pulses as short as 780 fs with center wavelength around 1042 nm, the average output power of 1.03 W and the peak power of 13.1 kW.     

基于高阶色散管理和相位共轭技术的色散补偿

相位共轭技术能够同时且高效地补偿二阶色散及非线性效应，且该技术同信号比特率、调制方式无关，是最有前景的色散补偿技术之一。理论分析了在高阶色散作用下，超短高斯脉冲信号在中距相位共轭通信系统中的传输演化特性，数值模拟了在二阶、三阶和四阶色散作用下，飞秒高斯脉冲信号在基于中距相位共轭技术的光纤色散管理链中的动态传输过程。结果表明，相位共轭技术和高阶色散管理相结合，不仅可以补偿和复原包括奇数阶和偶数阶色散在内的全部色散和非线性所引入的信号失真和畸变，而且能够减弱时分复用系统中脉冲之间的相互作用，使得信号在传输一个周期后恢复波形，从而提高了相位共轭系统对失真信号的补偿性能。     

Picosecond near- to mid-infrared optical parametric oscillator using KTiOAsO4

The operation and characterization of a high-repetition-rate singly-resonant picosecond optical parametric oscillator based on the non-linear material KTiOAsO4 and synchronously pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 81 MHz is described. By utilizing non-critical type II phase-matching in a 10 mm crystal, average near-infrared output powers of 403 mW have been generated at 31% extraction efficiency. The oscillator exhibits a pump power threshold of 230 mW and with the available mirror set can provide signal tuning over 1.116–1.281 μm and idler tuning over 2.260–3.160 μm by tuning the pump wavelength over 770–896 nm. Without dispersion compensation, near-transform-limited signal pulses with durations of 1.01–1.03 ps and idler pulses with 1.61–2.91 ps duration have been obtained for 1.2 ps input pump pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

基于交叉偏振波产生的脉冲净化技术研究与应用

本文利用交叉偏振波产生技术(XPW)对800 nm波段钛宝石飞秒激光器输出的激光脉冲进行时域净化, 提高脉冲时域对比度, 并测量验证了10¹¹对比度的脉冲, 达到测量仪器的动态范围极限, 比初始脉冲时域对比度有三个量级的提高, XPW的效率为22%. 同时发现净化后脉冲光谱宽度也得到一定展宽, 进一步利用啁啾镜对和补偿片对净化后的脉冲进行色散补偿, 得到25 fs脉宽的脉冲. 利用该净化后的激光脉冲作为种子注入已有的太瓦级钛宝石啁啾脉冲放大系统中, 在输出脉冲能量250 mJ, 宽度50 fs, 对应峰值功率5 TW的情况下, 在主脉冲前100 ps以外的范围内测量验证了10¹¹的脉冲对比度.     

Compensation for the self-steepening effects in optical fiber communication system using midway optical phase conjugation

Effects of self-steepening (SS) of chirped Gaussian pulses on optical fiber communication system using midway optical phase conjugation (OPC) are analyzed. Dynamic evolution of the ultrashort pulses is simulated numerically. It is found that OPC cannot compensate for pulse waveform distortion due to SS.The initial chirp of pulses and dispersion can counteract SS and improve the compensation performance for the distortion.