激光等离子体无源电探针探测及光谱诊断的比较分析

提出一种利用无源电探针探测激光焊接光致等离子体的方法。采用光电同步采集系统对激光焊接光致等离子体进行研究,利用无源电探针和光纤式光谱仪探测光致等离子体,利用等离子鞘层理论分析电信号,并运用相对光强法计算出光致等离子体的电子温度,比较同步光电信号分析结果。将不涂覆表面物质以及表面分别涂覆KF和TiO₂三种情况下的计算结果进行对比,对影响结果准确性的因素进行分析。研究结果表明通过无源探针法计算等离子体温度与光谱信号计算结果基本吻合,准确度受等离子体离子质量的影响。无源电探针法能够反映激光焊接光致等离子体内温度变化,具有较好的实时性,可以作为激光等离子体监测手段。     

Corrosion of Nickel-based Alloy G30 in the Stratum Water Containing H2S/CO2

The influences of temperature and CO2 pressure on the corrosion of nickel-based alloy G30 in the stratum water containing H2S/CO2 were investigated with the aid Mott-Schottky analysis and scanning electron microscopy（SEM） of electrochemical impedance spectroscopy（EIS）, The results indicate that alloy G30 is in the passive state in the stratum water, which is related to the formation of the passive film on its surface. This passive film can significantly protect the substrate from further corrosion. And the film protection is enhanced with decreasing temperature and CO2 pressure. Auger electron spectrometry（AES） and X-ray photoelectron spectrometry（XPS） results reveal that the passive film shows the double-layer structure, i.e. the inner chromium oxide and the outer iron/nickel spinel oxides or hydroxides with Mo oxides dispersing throughout the inner and outer scale.     

基于星载辐射计AMSR-E不同波段的北极海冰折射系数提取

海冰折射系数是一个重要的地球物理参数。利用Hong Approximation(HA)算法和星载辐射计AMSR-E数据,基于不同微波频段(6.9,10.7,23,37,89 GHz)实现北极地区不同季节海冰折射系数反演。首先对反演所用关键数据海冰密集度反演算法的系点进行优化,反演结果与验证数据平均偏差分别为3.00%和-0.50%,低于其它常用算法。结果表明：冬季一年冰和夏季海冰的折射系数反演结果在所有微波频段的平均值范围为(1.78~1.75)和(1.72~1.70),与前人研究结果基本一致,但冬季多年冰在较高频率的折射系数与前人结果偏差较大,高于10.7 GHz的微波频段不能用于冬季多年冰折射系数的提取;综合利用不同波段海冰折射系数反演结果能够有效识别沿岸冰间湖(比如冬季6.9 GHz),区分多年冰与一年冰(冬季89 GHz),并能确定多夏季海冰边缘融化范围(夏季6.9 GHz)。     

基于增益光纤长度优化的双波长运转掺铒光纤锁模激光器

构建了可自启动的双波长运转掺铒光纤锁模激光器.通过优化增益光纤长度,利用掺铒光纤在1530nm附近的再吸收效应调节激光器的增益谱,使激光器在1530nm和1560nm附近具有相同的增益强度.实验中采用31cm掺铒光纤作为增益光纤,以透射式半导体可饱和吸收体作为锁模器件,实现了自启动双波长锁模运转.激光器锁模输出重复频率为58.01MHz,信噪比为58.2dB,最高输出功率为4.8mW.锁模输出的光谱在1532.4nm和1552.3nm处具有两个强度接近的谱峰,谱峰间距约为20nm.该激光器无需手动调节即可实现双波长运转,更便于实际使用.     

A 12.1-W SESAM mode-locked Yb:YAG thin disk laser

Pumped by a 940 nm fiber-coupled diode laser, a passively mode-locked Yb:YAG thin disk oscillator was demonstrated with a semiconductor saturable absorber mirror(SESAM). 12.1 W mode-locked pulses were obtained with pulse duration of 698 fs at the repetition rate of 57.43 MHz. Measurement showed that the beam quality was close to the diffraction limit.     

Investigation of the Limit of Detection of an Infrared Passive Remote Sensing and Scanning Imaging System for Pollution GasEI北大核心CSCD

NECL could be used to estimate the limit of detection of the infrared passive remote sensing system. It was an important indicator of the sensitivity of the system. The theoretical equation of the NECL according to the atmospheric infrared radiation transfer model showed that NECL related to NESR, the brightness temperature of background and pollution gas, and the absorption coefficient of pollution gas. The remote sensing of SF6 was done. The limit of detection of the system at the different brightness temperature of background and pollution gas could be calculated. False color image of NECL was given from the measured data. The results show that NECL decreases rapidly by increasing the difference in brightness temperature of the background and pollution gas, the value of NECL was down to 10(-2) order of magnitude when the brightness temperature difference was equal to 30 K. False color image of NECL contributes to the discrimination of the limit of detection of the system in the complex background.     

基于光环路正交频分多址无源光网络的光拍频噪声避免方案及性能仿真(英文)

在正交频分多址无源光网络上行传输中,不同光网络单元的上行信号如果采用相同波长的不同激光器将会产生光拍频噪声,使得光网络单元的无色性难以实现.本文以正交频分多址无源光网络为研究对象,通过对系统结构的研究和相关公式的推导,分析了信号上行传输中光拍频噪声的产生原因和避免方式.针对下行发送上行载波结合光线路终端相干接收的光拍频噪声避免方案进行了仿真研究.分析了系统的抗色散方案以及色散累积和训练序列长度对系统性能的影响,给出了优化的参数设置,为系统实际应用提供了理论参考.     

基于柔性电路板单纤双向光纤组件的以太无源光网络单元研制(英文)

随着宽带接入技术的发展,以太无源光网络是光纤到户的一种备选方案.而光网络单元数量众多,其成本成为限制以太无源光网络技术实施的重要影响因素.本文提出了一种低成本以太无源光网络单元实现方式:采用带柔性电路板的单纤双向光纤组件直接安装在光网络单元的电路板上.为了验证弯曲柔性电路板的高速性能没有恶化,采用有限元方法仿真了弯曲柔性电路板的小信号响应.由于该方式没有独立的光收发模块,无法采用比特误码分析仪进行测试,因此提出了采用网络测试仪搭建光网络单元的光信号性能测试系统的方案并实现了对光信号的性能测试.结果表明:对于发射机,在0℃~70℃的范围内得到了超过10dB的消光比和1dBm的平均发射功率;对于接收机,估算灵敏度为-27dBm.     

超短脉冲光参量振荡器中TEM_(01)模经典增益的实现

用中心波长为850nm,重复频率为76MHz,脉宽为130fs的飞秒脉冲光产生二次谐波,泵浦TEM01模的同步光学参量振荡器,实验上获得了TEM01模大约4倍的经典增益,并给出了理论分析。这是产生高阶模飞秒脉冲光非经典频率梳的重要步骤,理论预计该增益下可以得到-2.20dB的TEM01模脉冲压缩光。     

Passive neutron area monitor with pairs of TLDs as neutron detector

A passive neutron area monitor has been designed using Monte Carlo methods; the monitor is a polyethylene cylinder with pairs of thermoluminescent dosimeters (TLD600 and TLD700) as thermal neutron detector. The monitor was calibrated with a bare and a thermalzed ²⁴¹AmBe neutron sources and its performance was evaluated measuring the ambient dose equivalent due to photoneutrons produced by a 15 MV linear accelerator for radiotherapy and the neutrons in the output of a TRIGA Mark III radial beam port.