飞秒写制长周期光纤光栅的液体浓度测量实验研究

利用逐点写入法在去涂敷层的普通单模通信光纤中直接写入了长周期光纤光栅(LPFG),实验获得的LPFG在C波段的谐振波长1 538.8nm,衰减强度达10.63dB。其氯化钠和蔗糖溶液浓度传感特性实验表明,随着盐溶液浓度的增大,LPFG的谐振波长向左线性漂移,盐浓度每增加1%,波长向左漂移约0.05nm;随着糖溶液浓度从0%增大为50%,LPFG的谐振波长向左非线性漂移量高达约8nm。实验结果表明:飞秒激光逐点写入法操作简单,容易控制诱导的周期性折射率微扰在纤芯和或包层的位置,从而制备出对低浓度液体敏感的LPFG化学传感器;同时飞秒激光写制的LPFG具有较高的外界环境灵敏度,有望用在化学浓度传感中。     

信号采样对Cs2LiYCl6:Ce3+探测器中子-伽马甄别性能的影响

针对核脉冲信号数字处理中采样率与采样深度对粒子脉冲形状甄别效果的影响问题,本文基于Cs₂LiYCl₆∶Ce³⁺(CLYC)探测器进行²³⁹Pu-Be中子场中子/伽马射线混合信号采集,研究几种中子/伽马射线脉冲波形甄别算法以及这些算法对波形采样率和采样深度的适应性。研究结果表明：基于积分算法的电荷比较法与内积算法的k-means聚类配合向量投影法对采样率、采样深度、噪声的适应能力都好于基于微分算法的脉冲梯度法;由于k-means聚类配合向量投影法对向量维度敏感,在抗低采样率方面不如改进的电荷比较法,而在抗低采样深度方面二者能力相当;XGBoost和LightGBM这2种机器学习算法在采样率降至12.5 MS/s和采样深度降至4 bit后仍可获得100%的甄别准确度,在波形采样率和采样深度较低时相比传统算法优势明显。     

透过率对Nd∶YVO_4/Cr~(4+)∶YAG激光器被动调Q锁模的影响

文章用实验的方法研究了输出镜透过率和Cr4+∶YAG晶体的初始透过率对Nd:YVO4/Cr4+∶YAG激光器被动调Q锁模的影响,通过对实验结果的分析得到如下结论:输出镜透过率较低时,调Q脉冲宽度增加,调Q脉冲包络中包含的锁模脉冲个数增加,相应的脉冲包络所包含的能量增加。输出的锁模激光的功率减小;当Cr4+∶YAG晶体的初始透过率较高时,调Q锁模脉冲激光的调Q包络宽度变大,调Q脉冲包络中包含的锁模脉冲个数增加。在大功率泵浦时,锁模深度明显加深。     

The Distortion of Energy Deposit Distribution of (12)～C Ions in Water

The transport process of 12C ions in water was studied with SRIM code and Geant4 toolkit.The SRIM results indicate that the transverse diffusion of 12C ion beam causes distortion of energy deposit along the beam direction.The distortion becomes more notable as the trans-verse diffusion increases.The simulation results of Geant4 indicate that the influence of secondary fragments on energy deposit distribution would be the main factor causing the distortion in higher energy range.In the region adjacent to the beam line where the contribution from 12C ions domi-nates,the contributions from secondary fragments are ignorable.The further from the beam axis the region locates,the larger the contributions from secondary fragments,until the contributions from secondary fragments are ignorable.The further from the beam axis the region locates,the larger the contributions from secondary fragments,until the contributions from secondary frag-ments exceed that of 12C.Among all the secondary fragments,the contributions of H,He and B ions are mostly notable.It is also found that some positron-emitting secondary fragments could be very useful for position emitting tomography (PET).