啁啾镜的优化设计

激光腔内的色散补偿问题是获得窄脉冲的关键,所以色散补偿元件的选择非常重要.传统的色散补偿元件棱镜对可以对二阶色散(群延迟色散)进行较好的补偿,但对高阶色散的补偿却无能为力.本文介绍了色散补偿元件啁啾镜的基本原理和优化设计思想,阐述了优化设计的基本过程,并根据激光腔内增益介质的实际色散情况,通过计算机模拟进行了相应啁啾镜设计的优化计算,以期保证啁啾镜在更宽的波段范围内能够获得相对较为稳定的色散补偿,尤其是对高阶色散的补偿.通过优化计算结果具体分析了影响啁啾镜色散补偿特性的几个重要因素,如色散量、色散带宽、膜层数以及单一膜层的厚度变化等对啁啾镜光学特性造成的影响都比较大.其中色散量的控制和色散带宽的选择是其中最重要的优化设计指标.(OB22)     

负色散镜的设计、制备及在掺钛蓝宝石激光谐振腔内的使用

根据钛宝石激光器的要求设计了性能优良的两种负色散镜(NDM1和NDM2)。NDM1同时引入啁啾效应和G-T效应产生大的群延迟色散量以减少光在负色散镜上的反射次数。NDM2仅引入G-T效应产生较小的群延迟色散以补偿腔内自相位调制带来的部分啁啾。选用离子束溅射法制备了这两种负色散镜。用分光光度计测试了它们的透射率。结果表明,所制备的负色散镜的性能与设计性能非常接近。使用这两种负色散镜进行掺钛蓝宝石激光谐振腔内色散补偿实现了飞秒脉冲锁模,获得了15 fs的超短脉冲。     

飞秒脉冲钛宝石激光器中的低振荡高色散镜对

基于高反射膜层和Gires-Tournois(G-T)腔,优化设计了一对低振荡高色散镜。该色散镜对的中心波长为800 nm,能够在680～920 nm的带宽范围内提供-200 fs~2的平坦的群延迟色散。基于双离子束溅射工艺,利用Nb_2O_5和SiO_2制备了低振荡高色散镜对,并将其应用于800 nm钛宝石激光器系统。通过高色散镜对2次,100.8 fs激光脉冲被压缩至19 fs。     

色散渐减光纤环形腔镜非等比耦合传输特性研究

利用光纤环形镜对脉冲进行压缩有着消除脉冲基座的优势而被广泛采用。传统的色散递减光纤构成的环形腔构成都采用50∶50的耦合器,本文通过对不同脉冲宽度及不同类型色散递减光纤构成的环形腔镜研究,分析发现采用60∶40的非等比耦合器较50∶50的耦合器构成的环形腔镜能够获得更高压缩质量的输出脉冲。     

自启动飞秒钛宝石激光器空间色散的补偿

对于棱镜对补偿色散,半导体可饱和吸收反射镜(SESAM)启动锁模的振荡级,用反转镜将从输出镜输出的光折进腔内,有效地利用腔内棱镜对补偿了棱镜对臂输出产生的空间色散,获得了高质量的光斑模式,输出光谱宽度为51nm,脉冲宽度为26．7fs。     

色散斜率对光纤环形镜开关特性的影响

从相位的角度入手研究了高阶孤子在非线性环形腔镜中传输的特性，发现用环形腔镜得到的压缩脉冲与构成光纤环的光纤色散斜率有着密切关系，并且该斜率对光纤环形镜的开关特性也有重大影响。     

基于自动扫描光栅单色仪的光学腔色散测量

通过引入自动扫描光栅单色仪,实现了快速色散测量,极大程度地降低了载波包络偏频慢漂对测量准确度的影响,降低了测量复杂度,提高了色散测量精度。以815nm钛宝石锁模激光器作为光源,以自建的八镜光学腔作为参考,对厚度约为6.35mm的熔融石英窗片的群延迟色散(GDD)进行了测量,结果与Sellmeier方程给出的理论值相差1.2fs2,不准确度仅为0.5%。测得八镜光学腔在常温常压状态下的GDD为28.8fs2,比理论值低约12fs2,原因可归结为8片腔镜镀膜的不均匀性。     

利用光纤环形镜开关特性与孤子压缩效应获得无基座超短光脉冲

利用色散渐减光纤中高阶孤子非绝热压缩及非线性环形腔镜的消基座作用获得高质量无基座超短光脉冲.可以把波长为1.55 μm,脉宽为20 ps的光脉冲压缩为1.42 ps无基座超短脉冲.并与直接用色散渐减光纤的非绝热孤子压缩得到的同宽度光脉冲分别在光纤正负色散区传输进行了比较,发现用色散渐减光纤构成的非线性光纤环形腔镜获得的压缩光脉冲具有相对理想的波形和频谱结构,有利于在光纤中长距离稳定传输.     

飞秒脉冲激光器腔镜二、三阶色散的理论研究

详细研究了飞秒脉冲激光腔镜的结构参数及光束入射角对其二、三阶色散的影响。得出了反射单一定时，二阶色散和三阶色出量随着膜料折射率比值和镀膜层数的增加而变大，当这两个参量分别超过１．６７和２５层时，三阶色散开始振荡．另外发现光束入射均对三阶色散的影响比二阶色散明显。     

基于宽带高反镜色散补偿的高功率克尔透镜锁模飞秒激光器

半导体激光器泵浦的高功率飞秒激光器在工业加工和生物医学等领域中均发挥着重要的作用。一般而言，无论是被动锁模飞秒激光器还是克尔透镜锁模飞秒激光器，都需要在腔内引入一定的负色散平衡自相位调制，产生稳定的飞秒孤子。特别是随着平均功率的增加，腔内自相位调制增强，需要更多的负色散量进行平衡。常用的色散补偿器件有棱镜对、啁啾镜以及GTI(Gires-Tournois interferometer)镜等，棱镜对导致振荡器结构复杂，而啁啾镜和GTI镜的价格较为昂贵。实现了基于宽带高反镜色散补偿的高功率克尔透镜锁模运转，在泵浦功率为18 W时，利用Yb∶CYA晶体获得了平均输出功率为3.6 W、脉冲宽度为92 fs、100 min功率稳定性均方根值（RMS）为0.46%的稳定锁模脉冲，有利于进一步降低高功率飞秒激光器的成本。     

Noise variance due to stimulated Raman scattering among channels of a wavelength-division-multiplexed system

We calculate the noise variance created by stimulated Raman scattering between signal channels of a wavelength-division-multiplexed system, accounting for group velocity dispersion. The results show that the noise variance is significantly reduced in the presence of dispersion. When average dispersion is zero, we see the noise variance scale quadratically with distance, while nonzero average dispersion yields linear growth with distance.     

超短脉冲高斯光束经聚焦透镜的光场形式

考虑到激光腔模中光腰的频率依赖性 ,得到了超短脉冲高斯光束经消色差透镜聚焦后光场的解析形式 ,并讨论了此时透镜群速度色散对光束聚焦性质的影响。分析了单透镜色差和群速度色散对超短脉冲高斯光束聚焦的时间分布及脉冲波面的影响 ;比较了消色差透镜及单透镜中脉冲初始光腰尺寸对聚焦的影响。     

Modal dispersion and attenuation measurements of silicon nitrideand silicon oxynitride waveguides using a streak camera

By measuring short pulse propagation in silicon nitride and oxynitride waveguides fabricated on silicon, it has been possible to characterize both attenuation and group velocity dispersion accurately for the different modes that propagate. The method is self-calibrating, using the ratio between scattered light from forward and backward traveling pulses at a particular point on the waveguide. In principle, the group velocity data can be used to calculate the phase velocities for the different modes using known dispersion relations. The phase velocities were measured independently using a prism coupling technique, and the group velocities that could be derived from them matched the experimental data within a few percent. The resolution of the technique is limited mainly by amplitude fluctuations of the laser. The full-width-half-maximum resolution was at best about 12 ps but should be extendable to better than 5 ps     

Dispersion Properties of Magnetostatic Surface Waves in a Ferrite Plate with Dissipation

Dispersion of forward and backward (dissipative) magnetostatic surface waves is analyzed in the geometry of a plane-parallel in-plane magnetized ferrite plate with dissipation. The results of calculation of dispersion curves and characteristics of the group velocity as a function of the real and imaginary parts of the wave number are presented. A limitation on the dispersion curves and the group velocity with respect to the maximum value of the wave number has been revealed and interpreted on the basis of the aperiodic propagation mode. Practical recommendations for lowering of this limitation are given.     

Femtosecond optical pulse generation from a CW laser using anelectrooptic phase modulator featuring lens modulation

We report a novel electrooptic phase modulator featuring lens modulation and its application to the electrooptic chirping compression method for ultrashort optical pulse generation. In the pulse generation experiment, pedestal free optical pulses of 550 fs in width with a 16.25-GHz repetition rate were obtained by the group delay dispersion of a grating pair from a CW Ar laser. Furthermore, the electrooptic chirping compression method with the electrooptic phase modulator featuring lens modulation is applicable to the negative group delay dispersion as well as positive group delay dispersion     

Simulation of the Field Emission Arrays with Parallel Wedge Emitter, Gates and Co-Planar Lens

Using the particle-in-cell (PIC) simulation code MAGIC, the wedge emitter, parallel gate and anode with and without co-planar lens have been simulated. The electron beam streamlines and the X-V_x phase space have been evaluated, which show that the co-planar lens focuses the electron. Simulation results are presented for a single FEA's cell with the anode biased at 500V and spaced 100μm from the cathode, which indicated that the electron beam width at anode is about 60.2μm for without lens FEAs, after add the lens with ?70V, the electron beam width will be decrease to 8.1μm, meanwhile the maximum transverse velocity will decrease from ±1×10⁶m/s to ±1.46×10⁵m/s.     

Optical-Kerr-enhanced mode locking of a lamp-pumped Nd:YAG laser

We discuss the potential use of three new mode-locking techniques, namely additive-pulse mode locking, the combination of self-phase modulation and group velocity dispersion, and Kerr lens mode locking, as simple retrofits to enhance the performance of conventional multi-watt lamp-pumped Nd:YAG lasers. Of the three, we discard the APM technique because of structural and power-handling difficulties. We then discuss theoretically and confirm experimentally that the combination of SPM plus gain dispersion can lead to pulsewidth reduction by a factor of 2 to 2.5 but not more, in agreement with the analysis of Haus and Silberberg. Finally, while KLM can be very effective as a fast saturable absorber in many types of lasers, we find that its application to lamp-pumped YAG lasers is frustrated by instabilities in thermal focusing and transverse mode position characteristic of this type of laser     

钛宝石激光飞秒和皮秒脉冲的三种工作模式

在双光束泵浦的钛宝石激光器中,实现了飞秒和皮秒脉冲的独立自锁模、交叉锁模和多脉冲3种工作模式,分析了飞秒和皮秒激光腔内的群速弥散(GVD)、自相位调制(SPM)、交叉相位调制(XPM)、增益竞争和自振幅调制(SAM)。结果表明:独立自锁模工作模式下,GVD和SPM决定了自锁模激光脉冲的特性;交叉锁模工作模式下,飞秒和皮秒脉冲具有很高的同步性,脉冲间的抖动为517 fs,飞秒和皮秒激光腔的调谐范围分别为36nm和22 nm;多脉冲工作模式下,飞秒脉冲仍然是单脉冲,而皮秒脉冲分裂为3个次脉冲,间隔为426 fs。     

Group velocity of dielectric waveguide modes

The group velocity and dispersion of surface-wave modes propagating along a circular dielectric rod are computed and presented graphically in normalised form. The group velocity as each mode approaches the cutoff frequency is calculated approximately.     

Compensation of dispersion in optical fibers for the 1.3-1.6 μmregion with a grating and telescope

The transmission of ultrashort optical pulses over long distances in optical fibers is limited by pulse broadening due to group velocity dispersion. A grating and telescope dispersion compensator with group velocity dispersion of equal magnitude and opposite sign can compensate for the fiber dispersion. The possible benefits of such dispersion compensation in the 1.3-1.6-μm wavelength region are investigated. The results show that compensation of first-order dispersion at 1.55 μm in a fiber with zero dispersion near 1.3 μm is primarily limited by the second-order dispersion of the grating and the telescope compensator. For a wavelength slightly greater than the zero dispersion wavelength, both the first- and second-order group velocity dispersion can be canceled by the grating and telescope dispersion compensator, allowing transmission exceeding 100 Gb/s over 100 km