Stability of neodymium:YAG laser posterior capsulotomy in eyes with capsular tension rings

·AIM: To evaluate the stability of neodymium(Nd):YAG laser posterior capsulotomy in eyes with capsular tension rings(CTRs).·METHODS: A total of 60 eyes that underwent cataract surgery and laser posterior capsulotomy postoperatively were included in this retrospective cohort study. To evaluate the safety and stability of capsulotomy, changes in the size of posterior capsulotomy and anterior chamber depth(ACD) in three groups: the group without CTR, the group with 12 mm CTRs, and the group with 13 mm CTRs, at 1wk, 3, 12, and 15mo after capsulotomy, were compared. ·RESULTS: In the group without CTR and the group with 12 mm CTR, there was no significant change in ACD at every post-laser follow-up. In the group with 13 mm CTR, the ACD change was significant until 3mo after capsulotomy. In all groups, there was a significant increase in the area of capsulotomy between 1wk and 3mo post-laser. Between 3 and 12mo post-laser, only the group with 13 mm CTR showed a significant increase in the area of capsulotomy(P<0.01). ·CONCLUSION: Laser posterior capsulotomy is safe in all three groups. The capsulotomy and ACD become stabilized and have not shown significant changes since 1y postlaser, even with larger CTRs. The maintenance of centrifugal capsular tension can last longer with larger CTRs, and the stability of the capsulotomy site can be reached about 12mo after capsulotomy in pseudophakic eyes with larger CTRs.

Using Brillouin fiber-optic ring laser to provide base station with uplink optical carrier in a 10 GHz radio over fiber system

In this paper, a 10 GHz radio over fiber system is analyzed. The Brillouin fiber-optic ring laser is used in the center station （CS） to suppress the optical carrier for the modulation depth enhancement. Simultaneously, the Stockes wave induced by the Brillouin amplification injects and locks the Fabry-Perot （FP） laser to output a signal-mode optical source, which works as the uplink optical carrier.

Semiconductor Optical Amplifier (SOA)-Fiber Ring Laser and Its Application to Stress Sensing

We have developed a novel optical fiber ring laser using a semiconductor optical amplifier (SOA) as the gain medium, and taking advantage of polarization anisotropy of its gain. The frequency difference of the bi-directional laser is controlled by birefringence which is introduced in the ring laser cavity. The beat frequency generated by combining two counter-propagating oscillations is proportional to the birefringence, the fiber ring laser of the present study is, therefore, applicable to the fiber sensor. The sensing signal is obtained in a frequency domain with the material which causes the retardation change by a physical phenomenon to be measured. For the application to stress sensing, the present laser was investigated with a photoelastic material.

Continuous-Wave and Actively Q-Switched Diode-Pumped Er:LuAG Ring Laser at 1650 nm

We demonstrate a cw and actively Q-switched Er：LuAO laser resonantly dual-end-pumped by 1532nm fibre- coupled laser diodes. A maximum cw output power of 1.9W at 1650.3nm is obtained at a pump power of 25.5 W, corresponding to a slope efficiency of 43.3 %. In the Q-switched regime, the maximum pulse energy of 3.51 mJ is reached at a pulse repetition rate of 100 Hz, a pulse duration of 90.5ns and a pump power of 25.5 W. At the repetition rate of 400 Hz, the output energy is 2.12m J, corresponding to a pulse duration of 125.4 ns.

An experiment of dynamical behaviours in an erbium-doped fibre-ring laser with loss modulation

This paper reports a systematic experimental investigation on the dynamics in the low-frequency region in an erbium-doped fibre-ring laser with loss modulation. A rich variety of bifurcation is analyzed through the bifurcation diagram and structured with the concept of the winding numbers. The coexistence of multiple attractors and the crisis that appear in the saddle-node bifurcations, and an interesting structure of bifurcation which is similar to the bifurcations in high-frequency range, have been observed.

Mode decoupling in solid state ring laser based on stimulated Raman effect in polar crystals

In this paper we study the gain saturation induced mode-coupling control in solid state ring laser devices based on the stimulated Raman effect of the polar crystals in.order to realize solid state ring laser gyroscopes. We theoretically investigate the mode coupling induced by gain saturation between clockwise （CW） and counterclockwise （CCW） propa- gating laser modes. Because the CW and CCW running waves are pumped with counter-propagating lasers respectively, the independent coexistence can be ensured.

Investigation on the intensity noise characteristics of the semiconductor ring laser

Based on the frequency-domain multimode theoretical model, detailed investigations on the noise characteristic of the semiconductor ring laser （SRL） are first performed in this paper. The comprehensive nonlinear terms related to the third order nonlinear susceptibility Z3 are included in this model; the Langevin noise sources for electric field and carrier density fluctuations are also taken into account. As the injection current increases, the SRL may present several operation regimes. Remarkable and unusual low frequency noise enhancement in the form of a broad low frequency tail extending all the way to the relaxation oscillation peak is observed in any of the operation regimes of SRLs. The influences of the backscattering coefficient on the relative intensity noise （RIN） spectrum in typical operation regimes are investigated in detail.

Experimental investigation on chaos generation in erbium-doped fiber single-ring lasers

In this paper,the chaotic behaviors in an erbium-doped fiber（EDF） single-ring laser（EDFSRL） are investigated experimentally by using the loss modulation method.An electro-optic modulator（EOM） made of LiNbO 3 crystal is added to the system.Thus,by changing the modulation voltage and the modulation frequency of the EOM,the freedom of the EDFSRL system is increased.The chaotic characteristics of the system are studied by observing the time series and the power spectra.The experimental results indicate that the erbium-doped fiber single-ring laser system can enter into chaos states through period-doubling bifurcation and intermittency routes.

The λ-Characteristics of the Ring Laser Based on Non-Uniform SOA

Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and biophotonics fields, can be tuned at an ultra high speed up to Mega Hertz over 100 nm bandwidth range with high SNR and flatness output. A steady-state model and segmentation algorithms are employed to investigate the gain spectra of four kinds of non-uniform SOA and the lasing wavelength of the SOA-RL. It shows that the dependence of the lasing wavelength on the average width is stronger when the light propagates from narrower to wider end than conversely, and there are some particular structures to show ultra high stability lasing wavelength. It is supposed that the main reason could be the carrier density distribution along the propagation.

In-Line Inspection of Pipeline Defects Detection Using Ring-Type Laser

Pipeline plays a vital role in transporting fluids like oils, water, and petrochemical substances for longer distances. Based on the materials they carry, prolonged usage may cause the initiation of defects in the pipeline. These defects occur due to the formed salt deposits, chemical reaction happens between the inner surface and the transferring substance, prevailing environmental conditions, etc. These defects, if not identified earlier may lead to significant losses to the industry. In this work, an in-line inspection system utilizes the nondestructive way for analyzing the internal defects in the petrochemical pipeline. This system consists of a pipeline inspection robot having two major units namely the visual inspection unit and the power carrier unit. The visual inspection unit makes use of a ring-type laser diode and the camera. The laser diode serves as a light source for capturing good quality images of inspection. This unit is controlled by the Arduino in the power carrier unit which provides the necessary movement throughout the pipe. The inspected images captured by the camera are further processed with the aid of NI vision assistant software. After applying the processing function parameters provided by this software, the defect location can be clearly visualized with high precision. Three sets of defects are introduced in a Polylactide (PLA) pipe based on its position and angle along the circumference of the pipe. Further, this robot system serves as a real-time interactive image synchronization system for acquiring the inspected images. By comparing the actual and calculated defect size, the error percentage obtained was less than 5%.

Statistical Properties of a Ring Laser with Injected SIgnal and Backscattering

The statistical properties of a homogeneously broadened ring laser with an injected signal are investigated and the normalized two-mode intensity auto- and cross-correlation functions are calculated by a full saturation laser theory with backscattering. The theoretical predictions are in good agreement with the experimental measurements.Further investigation reveals that the backscattering can reduce the fluctuations in the system while the full saturation effect plays a major role when the laser is operated above threshold. It is also quite important to notice that the injected signal can drive the weak mode from incoherent light to coherent light.

Er^(3+)-Yb^(3+) Co-Doped Fiber Ring and Line Laser

Er3+-Yb3+ co-doped fiber of 2 m long is used as the laser gain medium. Two fiber lasers with different structures have been set up, one is the line cavity fiber laser with the dielectric mirror being replaced by an all-fiber reflecting mirror,the other is the ring cavity all-fiber laser. Both set-ups have achieved lasing operation at the wavelength of 1.53 μm. Pumped by the 1 064 nm light from all-solid-state Nd ∶YAG laser, the two fiber lasers at 1 530 nm are operational. Their output powers are 7.8 mW and 2 mW with 130 mW and 160 mW pump powers.

Fiber Grating Ring Laser in All Optical Communication System

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内燃机活塞环材料及表面处理技术研究现状与发展趋势

活塞环是内燃机中重要的零部件之一,该部件的摩擦损耗占内燃机总摩擦损失的26%。因此,活塞环材料的选用及其表面处理研究对于优化提升内燃机性能、延长服役寿命具有重要意义。简单介绍并总结了内燃机活塞环常用材料及其发展趋势,详细综述了激光表面织构技术、表面涂层技术以及表面复合技术在内燃机活塞环减摩抗磨方面的研究和应用现状。其中,激光表面织构技术(LST)可起到接纳磨屑、保持油膜等作用,从而降低活塞环表面摩擦和磨损,但由于织构形貌和几何参数特征对摩擦学性能的影响较为复杂,仍需结合实际工况进一步研究并优化。以镀铬、热喷涂、气相沉积及激光熔覆为代表的涂层技术也常用于活塞环的表面强化处理,但涂层材料种类繁多,难以形成统一的行业标准进而规模应用。此外,通过合理复合多种表面处理技术,比如微弧氧化与电泳沉积复合、超声滚压与离子渗氮技术复合、磁控溅射和低温离子渗硫复合等,可实现优势互补、发挥协同作用,有效改善接触表面的摩擦性能,为活塞环的减摩增寿研究开拓了新的思路。最后对未来活塞环材料开发应用及其减摩抗磨方面的研究发展进行了展望。

天文导航高精度自适应航姿与时间同步技术

船用天文导航设备因采用数学解算平台,在前端原始数采样时需进行滤波处理,数据输出与同步脉冲信号输出存在时延,一旦同步脉冲信号被干扰,对外输出数据将失去实时性。针对此问题,本文提出一种高精度自适应航姿同步技术,通过建立自适应基准脉冲为预处理模块与导航解算模块提供容错空间,结合外部时间信息实时进行时间同步自校正,避免同步信号丢失造成的时间同步异常,实现上级系统对船用导航系统多样化同步需求下高频实时数据输出。试验结果表明,该方法可行有效,可提高航姿信息实时性与可靠性。

基于SOA光纤环形激光器的分布式声传感系统

为了降低传统分布式声学传感器(DAS)系统复杂度并提高信噪比(SNR),提出了一种基于半导体光放大器的光纤环形激光器(SOA-FRL)的DAS系统。该系统用SOA-FRL取代了传统的DAS系统中的窄线宽激光器和脉冲调制器,实现了高稳定的光脉冲输出;采用双脉冲外差探测方法,实现了精确的声信号探测和声源定位。实验结果表明:在频率为1 kHz、幅值为1.14 rad的声信号作用下,所提系统的解调SNR高达38.25 dB,空间分辨率为12 m。

基于激光熔覆的缸套表面梯度材料制备及其摩擦学性能研究

目的研究功能梯度材料对缸套表面的抗磨减摩作用,提升缸套-活塞环配副的摩擦学性能。方法通过激光打标机在缸套表面制备具有30°角规则纹理排布的凹槽,在凹槽内采用同轴送粉的方式熔覆镍含量不同的铁基粉末,分析熔覆合金层的金相组织,并利用往复式摩擦磨损试验机研究在一定载荷压力下功能梯度材料缸套的摩擦学性能。结果熔覆层金相组织呈现梯度排布,熔覆层与基体材料分子原子交互扩散形成良好的冶金结合。牌号为350、镍质量分数为4.2%、铁质量分数80%的粉末所制备的功能梯度材料,减摩效果最为明显,相比未经处理的对照组,平均摩擦因数降幅为25.4%,且该组在试验中接触电阻的平均值最大,相比对照组提升了63.45%。牌号为330、镍质量分数为9%、铁质量分数为70%的粉末制备的缸套,表面支撑指数最高为0.78,相比于未处理的对照组,增幅达到35%,且试验组活塞环经摩擦后,磨损量均小于对照组。结论制备了30°角分布的功能梯度材料,能使得缸套-活塞环摩擦学系统在工作过程中摩擦副的润滑油膜厚度更厚,且在运行过程中更稳定,以减少摩擦力和降低摩擦因数。同时,增强其支撑能力和储存润滑油的能力,使所制备的缸套摩擦因数显著降低。牌号为350的材料,改善摩擦学性能的效果最优。

考虑时变效应的织构缸套润滑性能分析及试验研究

内燃机缸孔内的时变效应和气压变化对活塞环受力影响不可忽略,而织构形貌参数对发动机油耗性能的影响也有待深入研究。为此,构建考虑时变效应和缸内气体压力变化的织构化缸套-活塞环摩擦副的流体动压润滑模型,采用多重网格法求解模型获得润滑油膜压力分布规律,进而获得缸套-活塞环间的最小油膜厚度和摩擦力,并针对装配织构缸套的发动机开展台架试验。计算结果表明:缸内气体压力变化影响活塞环径向受力,时变效应使缸套-活塞环受挤压效应的影响;织构化缸套能够增加润滑油膜厚度、减少摩擦力,当微凹坑深度为4~7μm,织构面积密度较小如为5%、10%时,能够获得较佳的最小油膜厚度与摩擦力值。台架试验表明,与原发动机相比,装配织构缸套的发动机油耗性能明显改善,在中高转速下燃油耗降幅较为显著,油耗最大下降14.5%,而24 h机油耗减少26.48%。

测地激光陀螺反射镜法向位移影响分析

测地激光陀螺是一种基于Sagnac效应的测量地球自转角速度的惯性传感装置,可应用于世界时、大地测量学等领域。激光陀螺一般由压电陶瓷控制推移反射镜来提高稳频精度。针对稳频机构工作过程中球面反射镜的法向位移对谐振腔的影响,从环腔稳定性定义出发,不同于传统的光学矩阵分析谐振腔稳定性,而是使用更真实的射线追踪仿真对球面反射镜法向位移时谐振腔的出光稳定性进行分析。仿真结果表明,环腔的尺寸与球面反射镜的法向可位移范围呈正相关,实验测得可位移范围为1.492~1.695 mm左右,实验与仿真结果误差在1%内。本文对测地激光陀螺在稳频机构工作过程中的球面反射镜法向位移的影响进行了初步探究,研究结果对于测地激光陀螺的稳频控制及陀螺搭建有一定参考意义。

太阳系中太阳和行星的引力磁与Lense-Thirring效应

简述基本物理中引力试验的概况,特别是检测试验粒子绕中央旋转天体引起LenseThirring(LT)效应的研究进展。给出自旋质点在旋转体引力电磁(Gravitoelectromagnetism,GEM)中运动的Schiff公式。描述了检测地球LT效应的各种方法:激光测卫、GP-B、激光测月和环形激光陀螺,特别叙述了环形激光陀螺仪在地球科学上的应用,如地震、潮汐、地球自转、极移的检测,并给出了正在进行和未来更高精度测定LT效应的LARES、OPTIS等计划。叙述了检验火星LT效应的情况,包括用MGS测距资料、火星自然卫星Phobos和Deimos观测资料,以及今后发射绕火星探测器的建议。也谈及用太阳系行星(水星、金星、火星)测定太阳LT效应和未来采用国际空间站进行相对论检验的LATOR计划。最后,简述在脉冲双星、X射线双星和银心Sgr A*附近红外S系统恒星中引力场的广义相对论效应,以及我国开展该项工作的情况和提出的建议。