高功率光纤激光器二级抽运技术的理论分析

从理论上分析了高功率光纤激光器直接抽运和二级抽运的斜率效率和热管理问题. 计算结果表明:波长为975 nm的激光直接抽运产生波长为1070 nm的激光时,理论斜率效率为80%,但当抽运光功率为10 kW时,在强制水冷条件下纤芯极值温度也难以降到150 ℃以下;在二级抽运技术中,波长为1018 nm的激光抽运产生波长为1070 nm的激光时,若采用传统的包层抽运技术,其斜率效率不足20%,如果抽运功率填充因子由0.0025提高到0.1,则理论上斜率效率可由18.5%提高到80.9%,从而总斜率效率由15.5 关键词： 二级抽运 功率填充因子 斜率效率 热管理     

EFFECTS OF BLENDING CHITOSAN WITH PEG ON SURFACE MORPHOLOGY,CRYSTALLIZATION AND THERMAL PROPERTIES

Biodegradable blend films composed of chitosan and PEG with various composition ratios were prepared.The chemical structure of the blend films was characterized with FTIR and X-ray,which showed no chemical bond formations but certain interactions probably coming from the hydrogen bonds.Morphologies of these blend films were viewed using AFM and SEM,suggesting that pure chitosan film had a smooth surface structure and the blend films surface showed a plenty of holes with varying size.Through the DMA measu...     

基于Labview实现二频机抖激光陀螺角随机游走系数的计算

国军标法和Allan方差法是目前用于计算二频机抖激光陀螺角随机游走系数最常用的两种方法,基于Labview对两种方法分别编程并予以实现,计算结果表明两种方法计算出来的结果几乎相等,具有等价性;但在数据处理的过程中发现用国军标法得到的拟合系数有时为负,针对这一现象通过理论分析发现目前数据处理方法的不完善是导致国军标法拟合系数有时为负的根本原因,对现有方法提出改进并基于Labview编程实现,实验结果表明：改进后的数据处理方法不仅解决了国军标法拟合系数有时为负这一问题,而且拟合误差降低了近一个数量级。     

物理老化无规聚苯乙烯屈服机理的研究

利用机械拉伸,示差扫描量热(ＤＳＣ)以及溶剂深胀等方法研究了老化物的无规聚苯乙烯(α-ＰＳ)的应力屈服行为,并从凝聚缠结的观点对实验结果进行了解释,实验结果表明,经物理老化手的α-ＰＳ在拉伸过程中出现应力屈服峰实质上是逐步打开凝聚缠结的过程,凝聚结是合物非昌相在物理老化过程中相邻的两三条链的局部连段由于范德化吸引力的作用形成的一种有序结构,其作用能很弱,升温至Ｔg附近,机械拉伸至屈服点以及溶胀剂都可将其完全破坏.     

DETECTION OF T_g BY MODULATED DIFFERENTIAL SCANNING CALORIMETRY

The glassy transition of the polyethylene terephthalate (PET) sampleswhich have been subjected to solvent induced crystallization (SINC) was investigated bymodulated differential scanning calorimetry (MDSC) and density measurement. The dif-ferential of heat capacity signal, d C_p/dT from MDSC, was used to monitor the SINCprocess. It reveals that the T_g temperature shifts to higher value with the advancement ofSINC. When the toluene-immersing time was longer (168h), the detection of T_g becomemore difficult, because some smaller peaks emerged at the lower temperatures and theseare explained as the movement of small segments in the amorphous region. These observedresults are due to the morphology and structure introduced by the SINC process.     

基于计数法测量激光多普勒测速仪的测速精度

为了测量所设计的激光多普勒测速仪(LDV)的测量精度,用均匀转动的斩波片代替高精度的转台作为标准的速度源,并基于单片机AT89S52,采用光计数的方法测量斩波片上某一固定位置的切向运动速度,LDV的测量结果与之相比较。实验结果表明,LDV测速的相对精度不超过8‰,稳定性较好。     

EMD阈值滤波在光纤陀螺漂移信号去噪中的应用

光纤陀螺(FOG)的漂移输出经常淹没在噪声中,直接建模补偿漂移信号非常困难,提出基于经验模态分解(EMD)的阈值滤波方法(EMD-T)对漂移信号预处理。为了提高EMD分解的精确度,基于噪声传播模型引入一种有界噪声辅助分析的方法,将漂移信号中幅值小、频率高的噪声信息压缩至低阶本征模态函数中。为了验证算法的有效性,采集一款干涉型FOG的静态漂移输出作为测试信号,将EMD-T与基于小波包变换(WPT)和常规EMD(CEMD)的阈值滤波方法进行了对比分析。仿真结果及Allan方差分析表明,EMD-T较WPT和CEMD滤波性能有显著的改善,经EMD-T处理后,漂移信号的量化噪声(Q)和角度随机游走(N)分别由0.7862μrad和4.58×10-3(°)·h-1/2下降至0.1340μrad和9.03×10-4(°)·h-1/2。     

Effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier

Theoretical and experimental research on the effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier is carded out. The complex Ginzburg-Landau equation is used to simulate the propagation of the pulse in the fiber amplifier and the results show that pulses with negative initial chirp produce the widest supercontinuum and pulses with positive initial chirp produce the narrowest supercontinuum when the central wavelength of the pump lies in the normal dispersion region of the gain fiber. A self-made line width narrowing system is utilized to control the initial chirp of the nanosecond pump pulse and a four-stage master oscillator power amplifier configuration is adopted to produce a high power near-infrared suppercontinuum. The experimental results are in good agreement with simulations which can provide some guidance on further optimization of the system in future work.