A novel optical picosecond-duration NRZ-to-RZ format converter with simultaneous wavelength multicasting using a single-stage Mach–Zehnder modulator

We propose a novel and simple scheme to achieve NRZ-to-RZ format conversion and simultaneous wavelength multicasting based on a single-stage dual-arm electro-optic Mach–Zehnder modulator (MZM) and a short single mode fiber (SMF). The format conversion and wavelength multicast process are achieved by chirp compensation under the condition of generation of optical flat frequency comb. 40 Gb/s NRZ-to-RZ conversion with one-to-five multiple-wavelength channel multicasting and transmission of the NRZ and the converted signals over 200 km dispersion-managed fiber-link are successfully demonstrated by numerical simulation. Research results show that 40 Gb/s 2 ps RZ signal with wavelength-preserving can be obtained after format conversion. The converted RZ signal presents good transmission performance and can easily be multiplexed to 160 Gb/s using optical time division multiplexing (OTDM) technology. All the multicast channels can be error free after 50 km transmission. Besides, the conversion operation can also greatly reduce the timing jitter of the degraded NRZ signal due to the retiming function of the proposed scheme.     

Monitoring of laser heating temperature in laser spectroscopic measurements

During laser spectroscopic measurement, a part of laser energy will be converted into heat in the processes of excitation and light emission. Temperature monitoring can help to evaluate such nonradiative process. Upconversion luminescence of phosphor Y₂O₃:Er,Yb under laser excitation at 980 nm was investigated in this work. Point temperature of the phosphor was monitored using the fluorescent intensity ratio (FIR) technology. Laser induced temperature rising was identified by comparison with a theoretically ideal temperature calibration function: lnR = 3.1738–1167/T. The monitored temperature of laser heating rises monotonically with increasing laser power. Circumstances around heating point will modify the calibration function, but the linear slope of lnR ~ 1/T is constant.     

Modal prediction of atmospheric turbulence wavefront for open-loop liquid-crystal adaptive optics system with recursive least-squares algorithm

For an open-loop liquid-crystal adaptive optics system, its performance is mainly limited by the time delay. We propose a new modal recursive least-squares (RLS) predictive algorithm to overcome this problem. The RLS algorithm has a simple architecture, low computational complexity and a high converging speed. The impact of the number of the foreword prediction frame N and the number of the predictor order M of the RLS predictor is analyzed in detail. The results show that the best foreword prediction frame N must be equal to the system loop delay frame SLDF. The appropriate predictor order M of the RLS predictor is equal to 2 or 3 when there is no measurement noise and it depends on noise ratio N_R when the measurement error cannot be neglected. We present numerical simulations to show the significant improvements brought by the RLS predictor.     

Optimization of the three-dimensional electric f ield in IH-DTL

The tuning process of the three-dimensional electric field near the beam axis is very important in the optimization of the Interdigital H-mode Drift Tube Linac (IH-DTL). The tuning of the longitudinal field distribution, the Kilpatrik (Kp) factor, and the transverse dipole field have been discussed in detail, combined with the radio-frequency tuning process of the 53.667 MHz short IH-DTL cavity, which was designed to accelerate ²³⁸U³⁴⁺ from 0.143 MeV/u to 0.289 MeV/u in the SSC-Linac injector project at the Institute of Modern Physics. The flatness criterion and the tube tuning method are discussed in order to meet the beam dynamics requirements. In the tube tuning process, the energy gain error in the cells should be reduced to less than ±2%, and the Kp factor should be reduced to 1.6. The transverse dipole field and the method that uses a "plunger" to dismiss this dipole field are evaluated. The experience gained from the first cavity optimization benefits the tuning process of the three remaining IH-DTL cavities in the SSC-Linac project.     

Study of measuring methods on spatial resolution of a GEM imaging detector

In this paper, the limitations of the common method measuring intrinsic spatial resolution of the GEM imaging detector are presented. Through theoretical analysis and experimental verification, we have improved the common method to avoid these limitations. Using these improved methods, a more precise measurement of intrinsic spatial resolutions are obtained.     

K3B6O10Br非线性光学晶体的生长及性质研究

采用顶部籽晶法,KF.2H2O-PbO复合助熔剂生长K3B6O10Br晶体,获得了18 mm×18 mm×10 mm尺寸的单晶。K3B6O10Br紫外透过截止边约为210 nm,粉末倍频效应为3倍KDP,利用德拜公式计算了阴离子基团的偶极矩。采用直角棱镜法测试了晶体折射率并拟合了Sellmeier方程。计算及实验表明,K3B6O10Br能够实现532 nm及355 nm倍频输出。对晶体的激光损伤阈值、硬度及潮解性进行了测试。     

中温太阳能与化学链燃烧整合的冷热电系统

本文提出了中温太阳能与二甲醚-氧化钴化学链燃烧整合的新颖冷热电联产系统,并对系统热力性能及关键参数对系统热力性能的影响进行了分析。研究表明,燃气透平入口初温(TIT)1000℃,压比8.8时,新系统的总能效高达92.6%。在输出量相同的情况下,新系统的化石能源节能率达29.3%,太阳能集热面积节省率可达69.8%。同时,采用热重分析仪对系统关键过程—二甲醚-氧化钴化学链燃烧开展了初步的实验研究,验证了新系统的可行性。     

一次人工触发闪电上行正先导的传输特征

利用山东一次人工触发闪电的高速摄像和30 m, 60 m和480 m的同步电场测量, 清晰显示了人工触发闪电上行正先导的传输特征.上行正先导头部光强相对较强, 二维发展速度变化波动较大并呈现明显不规则性,表明上行正先导发展具有明显的梯级特征. 在先导开始阶段从340 m到705 m高度之间上行正先导平均发展速度为9.8×10⁴ m/s,起始速度是 3.8×10⁴ m/s,局部速度总体上随高度呈现增加趋势.电场变化在近距离产生有规律的梯级状 变化,记录到的28个梯级相邻梯级间隔变化从14 μs 到 39 μs,几何平均值为25.1 μs. 估计的先导梯级长度分布在0.9 m到3.7 m,几何平均值为1.7 m.先导电场变化由慢的正向梯级状变化和 脉冲变化组成,结合光学和电场变化测量结果,得出正先导头部通道发生弯曲可使其电场变化的梯级特征减弱 或消失;正负先导梯级形成机制可能类似,均由其先导头部前端的双向流光发展而来.     

自主研制核磁共振波谱仪的性能评估

主要介绍自主研制500 MHz核磁共振谱仪的性能评估情况,旨在建立一台功能完整的核磁共振波谱仪. 首先利用系统调试使控制台各个硬件单元在用户软件控制下实现NMR实验中的基本功能,然后通过性能测试保障功率线性度、信号稳定性和场频联锁的可靠性,实验验证了谱仪溶剂峰压制的效果,并获得良好的探头线形指标（0.43/5.46/10.73 Hz）和¹H灵敏度指标（信噪比为728∶1）,表明自主研制500 MHz核磁共振波谱仪系统能够满足常规核磁共振实验需求.     

分离扇回旋加速器的等时场在线优化

针对兰州重离子加速器冷却储存环（HIRFL-CSR）的分离扇回旋加速器（SSC）的等时场优化问题,依托HIRFL-CSR的主数据库系统Oracle,设计了系统控制界面,该界面不仅能够读取和给定电源电流值,而且能够实时更新束流相位信息。根据束流相位的实时数据,利用Kb-Kr方法以及Lagrange插值算法建立的等时场,实现了对SSC束流等时场的在线优化。优化后的等时场可以有效控制束流相位的漂移,提高束流品质。