Soft modes in ferroelastic LaP5O14 and NdP5O14

We have observed an underdamped, temperature dependent optical phonon in the non-polar ferroelastic compounds NdP₅O₁₄ and LaP₅O₁₄. These materials exhibit a second-order displacive phase transition from C_2h to D_2h point group symmetry at temperatures slightly above ambient. The soft mode is observed in both phases.     

Photorefractive two-step recording in a piezoelectric La3Ga5SiO14 crystal doped with praseodymium

The first experimental verification to the authors' knowledge of efficient two-step recording in a photorefractive and piezoelectric crystal of La(3)Ga(5)SiO(14):Pr(3+) with cw laser light (I<20W/cm(2)) is reported. We found nonlinear behavior of the photorefractive sensitivity and photovoltaic current, indicating that the excitation process is connected to excitation of 4f(2) electrons of the Pr(3+) dopant through an intermediate level to the conduction band. This two-step nature of the photorefractive effect makes the crystal an exciting new candidate for applications in holographic storage.     

Laser-induced damage and periodic stripe structures of a CaF_2 single crystal by an ArF excimer laser

The laser-induced damage threshold of a calcium fluoride(CaF2)single crystal was obtained by a 193 nm ArF excimer laser.The damage morphology of the crystal was analyzed.The results showed that the surface of CaF2 single crystal broke along the natural cleavage plane under ArF excimer laser irradiation,some fragments fell off,and Newton’s rings were observed on the curved fragments.Laser-induced periodic stripe structures(LIPSS)appeared on the surface layer beneath the fragments that peeled off.The spacing of LIPSS was measured,and the formation mechanism of LIPSS was analyzed based on the interference model.     

含周期性空腔结构吸声机理的研究

为了研究水下含周期性空腔结构的吸声机理,建立并验证了含轴对称空腔周期性结构吸声特性计算的简化有限元仿真方法,用简化的有限元模型结合遗传算法对水下环境含周期性圆柱空腔结构的吸声性能进行了优化设计.从能量耗散、变形和模态的角度分析了含周期性空腔结构的吸声机理.空腔结构谐振包括表层的弯曲振动和空腔附近的径向变形,且径向运动也...     

SmxLa1-xP5O14和DyxY1-xP5O14晶体的荧光寿命研究

本文用脉冲衰减法和时间分辨荧光光谱法测量了六种不同稀土离子浓度的SmxLa1-xP5O4晶体的4G5/2→6HJ(J=5/2,7/2,9/2,11/2)四个能级和七种不同稀土离子浓度的DyxY1-xP5O14晶体的4F9/2→6HJ(J=15/2,13/2,11/2,9/2)四个能级的荧光寿命和荧光强度。结果指出,在这类晶体中,Sm3+和Dy3+的荧光寿命随着离子的浓度增加而变短,存在着严重的荧光浓度猝灭现象。最后还讨论了浓度与寿命,寿命与荧光强度的关系。     

稀土五磷酸盐(REP5O14)晶体的光谱性质

本文在较前人宽的波段内系统地研究了REP5O14(RE=Ce3+,Pr3+,Nd3+,Sm3+,Eu3+,Gd3+,Tb3+,Dy3+,Ho3+,Er3+,Tm3+,Yb3+)单晶的吸收光谱、激发光谱与荧光光谱.合理地确定了谱项.关于SmP5O14,GdP5O14,DyP5O14,TmP5O14与YbP5O14等晶体光谱的研究,至今尚未见报导.这些晶体系统的光谱数据,对于了解它们的性质及其应用方面,都是很有用的.     

Laser site-selection time-resolved spectroscopy of NdP5O14

Laser site-selection spectroscopy shows the presence of Nd ions in non- equivalent crystal field sites in NPP. Time-resolved spectroscopy indicates that energy transfer does not take place between ions in these different types of sites.     

Analysis of periodic thin-film structures with rectangular profiles

A rigorous analysis is presented for thin-film structures on which a rectangular-profile grating layer is superimposed. Typical dispersion curves are calculated for guided leaky waves, which are relevant to beam couplers in integrated-optics applications.     

五磷酸铈、锰晶体的发光

本文用蒸发溶液法生长了一系列CeP5O14:Mn晶体,测定了它们的组成和结构.测定了晶体的吸收光谱,激发光谱和发射光谱,观察到Ce3+→Mn2+之间的能量转移和在此体系中锰离子在545nm附近和665nm附近两个波段同时进行发射,并随着锰含量的增加,665nm的荧光强度下降而545nm的强度增加.     

超短脉冲激光诱导周期性表面结构

激光诱导周期性表面结构（Laser-induced periodic surface structures,LIPSS）具有纳米尺度的特征结构和自重复的微观尺度的排列图案,因此,LIPSS在传感器、太阳能发电、光催化等方面具有广泛的应用前景。本文首先介绍LIPSS形成过程中超快激光与物质相互作用的复杂过程,强调瞬态光学性质和表面结构变化的作用。然后综述几种具有代表性的LIPSS形成机理,并且讨论了各自的优缺点。接着介绍了LIPSS形成过程中材料的变化,主要包括材料化学成分、晶体结构和表面微观结构的变化。最后综述了LIPSS在材料表面处理、光学和机械等方面的应用。     

Laser emission from polished NdP5O14 crystals with directly applied mirrors

We report on crystal processing, laser fabrication, emission spectra and output characteristics of neodymium pentaphosphate lasers. We obtained cw oscillation with an output power of 19 mW from a crystal with dielectric mirrors directly applied on polished (001) planes. We pumped longitudinally with 280 mW of an argon ion laser at 514 nm focussed to a 94-μm diameter. Near threshold our laser operated in the vicinity of 1053 nm; when pumped 1.6 times threshold it operated dominantly in the vicinity of 1063 nm.     

Dynamic analysis of periodic structures

The natural vibration analysis of a periodic structure with repeated identical substructures may be simplified by using some symmetrical properties of the substructure dynamic matrices, resulting in a set of linear difference equations in the displacements. These equations are readily solved for cyclic symmetric systems, simply supported systems and infinite systems. The order of the overall frequency equations is at most equal to one half of the total number of degrees of freedom retained for a single substructure regardless of the number of substructures in the system. With these natural modes, the system with general boundary conditions at end stations is analyzed by a fast converging method.     

Self-organized periodic photonic structure in a nonchiral liquid crystal

A hybrid-aligned cell of the smectic A liquid material 8CB gives two stable director configurations, one of which is periodic and gives strong diffraction of light. This photonic lattice director profile arises from "frustration" caused by conflicting constraints imposed by the boundary conditions and the constant amplitude smectic density wave. A model is proposed which accords well with the experiment results, predicting correctly the dependence of the periodicity on the cell thickness and reproducing optical polarization microscopy results.