The disorder effect on the performance of novel waveguides constructed in two-dimensional amorphous photonic materials

On the basis of two-dimensional amorphous photonic materials,we have designed a novel waveguide by inserting thinner cylindrical inclusions in the centre of basic hexagonal units of the amorphous structure along a given path.This waveguide in amorphous structure is similar to the coupled resonator optical waveguides in periodic photonic crystals.The transmission of this waveguide for S-polarized waves is investigated by a multiple-scattering method.Compared with the conventional waveguide by removing a line of cells from amorphous photonic materials,the guiding properties of this waveguide,including the transmissivity and bandwidth,are improved significantly.Then we study the effect of various types of positional disorder on the functionality of this device.Our results show that the waveguide performance is quite sensitive to the disorder located on the boundary layer of the waveguide,but robust against the disorder in the other area in amorphous structure except the waveguide border.This disorder effect in amorphous photonic materials is similar to the case in periodic photonic crystals.     

Experimental investigation of the impact on nearby solid boundary during laser-generated bubble collapse

Cavitation damage has been considered as being responsible for many effects in hydraulic machinery and biological medicine. In order to better understand the cavity interaction with nearby solid surfaces, the impact loading induced by the high-speed liquid-jet and subsequent jet flow during the final stage of the bubble collapse in a static fluid is investigated by focusing a Q-switched pulsed laser into water. By means of a new method based on a fibre-coupling optical beam deflection technique, a detailed experimental study has been made to clarify the relationship of the impact pressure against a solid boundary as a function of the dimensionless γ that is generally used to describe the bubble dynamics with its definition γ= s/R_{max}(R_{max} being the maximum bubble radius and s denoting the distance of the cavity inception from the boundary). The experimental results are shown that for γ in the range of about 0.67 to 0.95 with a pulsed laser energy 230mJ, the transient pressure applied on the solid surface is maximum; while for γ>1 or γ<0.67, it is gradually decreased. By combination of our experimental results with the other work that detected the acoustic emission during the bubble collapse at different γ, it is concluded that in this range of 0.67－0.95, the destructive effect due to a liquid-jet and the following jet flow impact actually outweighs the well-known effect of shock wave emission and plays a vital role during the cavitation bubble collapse.     

超短激光脉冲在水中的非线性传输特性研究

基于扩展的非线性薛定谔方程及与其耦合的电子密度演化方程,理论研究了超短激光强脉冲在水中的非线性传输特性.理论模型综合考虑了衍射、正常群速度色散,多光子吸收、自聚焦及激光诱导产生的等离子体对光脉冲的自散焦效应.采用有限差分法模拟得到超短脉冲在传输过程中轴向上光功密度和等离子体密度的时空分布.系统分析了超短脉冲在水中传输的动力学过程,讨论了非线性自聚焦和等离子体自散焦效应在脉冲传输过程中的竞争关系.同时研究了不同入射激光能量,脉宽和聚焦条件对等离子体丝的时宅结构和脉冲能流横向分布的影响.该研究将有助于理解和推动超短光脉冲在激光医学、激光安全防护和水中激光加工中的应用.     

Three-channel dual-wavelength fiber laser based on a digital micromirror-device processor and photonic crystal fiber

A stable three-channel dual-wavelength fiber ring laser is proposed and experimentally demonstrated. The digital micromirror-device(DMD) processor can select and recirculate any dual waveband from the gain spectrum of the erbium-doped fiber at each channel. The uniform and stable dual-wavelength oscillation is obtained by a highly nonlinear photonic crystal fiber, which causes two degenerate the four-wave-mixing processes. By loading different reproducibility diffraction gratings on the optoelectronic DMD processor, the laser can be operated stably in a three-channel dual-wavelength scheme at room temperature. The power fluctuation of each laser channel is less than ～0.02 d B.     

波前函数法在光波干涉教学中的应用

本文介绍了波前函数的概念,并利用波前函数法分析讨论了光的杨氏双缝干涉和薄膜干涉现象.传统光程法在讨论两列波干涉时比较直观简单,但在讨论多列波干涉的情况下,光程法简单性的优势将无从体现.和传统的光程法相比较,在讨论多列波相互叠加时,波前函数法的优势凸显,另一方面,波前函数法充分体现了波动的物理思想,刻画出电磁波的传播和叠加的物理图像,有助于学生深层次理解波动概念.     

影响基于等厚干涉原理测量膜厚精度的因素分析

基于光学干涉原理的薄膜测量技术是重要的光电检测技术之一.该测量方法可获得较高的测量精度.但是在实际干涉测量中,膜厚测量的精度与所用光束的物理特性以及膜厚本身有较大关系.基于薄膜干涉的基本原理,分析了光束的发散角、薄膜厚度以及光束的入射角对基于薄膜干涉测长结果的影响,这对学生正确理解基于干涉的测量原理,掌握正确的测量方法,提高测量精度具有一定的指导意义.     

激光等离子体及点爆炸空气冲击波波前运动方程的研究

根据激光等离子体空气冲击波在自由空间中传播的约束条件导出的空气冲击波前运动方程与点爆炸波泰勒解进行比较,证明泰勒解是该冲击波波前传播方程在中场的近似形式.并将该冲击波运动方程与强爆炸空气冲击波的实验进行比较,计算结果与实验数据符合得非常好 关键词： 激光 核爆炸 等离子体冲击波     

二维八重准晶有机光子晶体平板的光学传播特性

采用时域有限差分法研究了二维八重准晶有机光子晶体的光传输特性,重点分析了光束在聚苯乙烯空气柱平板结构和聚苯乙烯介质柱结构中的透射特性与光局域特性。研究结果表明,即使在低折射率对比度的情况下,两种完整八重准晶平板结构中均出现了可见光波段的光子带隙和本征模,且光子带隙中心位置随着平板厚度的增大而红移。当在两种准晶结构中引入缺陷微腔时,带隙内的缺陷模产生位置和波长红移特性随着微腔结构的变化规律明显不同,这种差异性是由两种物理机制(即光子晶体缺陷能级变化与微腔所支持的驻波条件)共同作用的结果。这一研究结果将为实验制备有机准晶发光器件提供一定的理论基础。     

基于数字微镜器件的多通道C波段可调谐光纤激光器

可调谐光纤激光器可广泛应用于光纤通信、光纤传感、激光光谱、精密测量和激光加工等诸多领域。针对目前可调谐激光器在调谐性、灵活性、稳定性和多波长功率均衡性等方面的不足,提出一类新型的基于数字微镜器件(DMD)的多波长宽带可调谐光纤激光器。该激光器利用关键器件DMD作为波长调谐器,掺铒光纤作为激光增益介质,通过巧妙的光学设计,实现仅利用一块DMD芯片独立、灵活、稳定调谐多波长激光输出的目的。该激光器具有3个输出通道,各通道之间独立开关控制,每个通道均可实现波长在1530~1560nm之间的连续可调谐输出,波长调谐精度0.055nm/pixel,边模抑制比大于55dB,激光输出功率最大值为10mW,2h内的中心波长漂移小于0.02nm。