新型红外非线性光学晶体SrCdGeSe4生长与性质表征

锶镉锗硒(SrCdGeSe4)晶体是近期被发现的一种性能优异的新型红外非线性光学材料.本研究采用自制的双温区管式炉成功合成出SrCdGeSe4多晶,单次合成量达到300 g;采用坩埚下降法首次生长出SrCdGeSe4单晶,尺寸为φ27 mm×80 mm;通过定向、切割和抛光等程序,得到几个不同尺寸的定向SrCdGeSe4晶片,选取一片8×8 ×2 mm3双面抛光(110)晶片测试了摇摆曲线、红外透过光谱和激光损伤阈值.结果 显示:(220)摇摆曲线半峰宽为44.8",该晶体的短波透过截止边为596 nm,且在1～ 14 μm波长范围内透过率超过68;;另外,晶体在Nd∶ YAG脉冲激光,脉宽5 ns,重复频率1 Hz,光斑直径0.15 mm测试条件下,激光损伤阈值为530 MW/cm2.     

基于法布里-珀罗腔产生飞秒激光脉冲串在硅表面诱导高质量亚波长周期条纹(特邀)EI北大核心CSCD

为了制备高质量表面周期结构,利用法布里-珀罗腔对飞秒激光进行时域整形,输出子脉冲间隔在1~300 ps内灵活可调的飞秒激光脉冲串,在硅表面诱导亚波长周期条纹。实验结果显示,利用飞秒激光脉冲串诱导得到的亚波长周期条纹明显优于原始高斯光诱导的亚波长周期条纹。利用子脉冲间隔为100 ps的脉冲串诱导的亚波长条纹最佳,条纹周期为1008 nm,结构取向角为2.8°,边缘粗糙度为3.9 nm,可达到光刻工艺的标准。     

双向血流超声多普勒信号的小波降噪

利用小波框架结合软阈值的方法对表征双向血流的超声多普勒信号进行降噪。为了避免软阈值非线性处理对双向血流多普勒信号方向表征的影响,先对超声多普勒信号进行方向分离,然后对分离后的信号分别进行小波降噪,最后合成降噪后的双向血流超声多普勒信号。对计算机仿真的股动脉超声多普勒血流信号的降噪实验结果分析表明:本方法在不影响双向血流信息的前提下,提高了多普勒信号的信噪比、最大频率曲线和平均频率曲线的估计精度。仿真实验的结果证明了本方法可以用于双向血流超声多普勒信号的降噪。     

颈动脉多普勒信号自回归滑动平均模型极点特征及分类应用

对颈动脉多普勒血流信号实现了一种基于自回归滑动平均(ARMA)模型、并采用反向传输(BP)神经网络分析ARMA模型极点特征的系统,以达到诊断脑梗塞疾病的目的。首先对音频颈动脉多普勒血流信号分时间段建立ARMA模型,得出模型极点分布的特征参数,研究这些特征参数对脑梗塞疾病诊断的敏感性,然后对敏感的特征参数利用BP神经网络进行分类,对是否存在脑梗塞的血流状况进行判别。共使用474例颈动脉血流信号来建立合适的神经网络,使用52例信号进行测试,结果表明:系统训练和测试的正确率均大于94%,可以满足临床的要求。     

一个无电场成形电极平面漂移室的研究

本文叙述了一个平面无电场成形电极漂移室的一些基本特性, 测量了探测效率、漂移时间与漂移距离的关系及不同位置的电荷谱.     

Measurement of the Carrier Recovery Time in Semiconductor Optical Amplifier Based on Dual-Pump Four-Wave Mixing Technology

A scheme of measuring the carrier recovery time in semiconductor optical amplifiers （SOAs） based on dual pump Four-wave mixing technology is presented. The carrier recovery times under 120mA, 180mA 240mA and 300mA injected currents are measured to be 111ps, 81ps, 71ps and 53ps, respectively. The carrier recovery time of the spacing between the two umps is also investigated. The experimental results show that the conversion efficiency keeps constant when the spacing of the two pumps varies within a small range.     

超短脉冲抽运下频率一致纠缠光源量子特性实验研究

利用自发参量下转换过程产生的频率纠缠光源在量子信息处理及相关领域中 具有十分重要的应用. 本文利用中心波长为792 nm, 脉冲宽度小于20 fs的脉冲激光源抽运满足II类准相位 匹配条件的周期极化磷酸氧钛钾晶体, 实验产生了偏振相互正交的频率一致纠缠光子对. 基于Hong-Ou-Mandel干涉仪的二阶量子符合干涉装置, 测量到该纠缠双光子对的干涉可见度约为42%, 表明其频率不可分特性较理想频率一致纠缠光源大大降低. 通过理论分析给出, 由于超短脉冲光源对应的宽频谱带宽影响, 相位匹配函数中的高阶色散项不再忽略, 从而导致纠缠光子对的频率不可分性减弱. 进一步利用实验参数给出的数值模拟结果与实验结果符合, 证实了脉冲抽运源带宽对频率一致纠缠光源的量子不可分特性的影响. 关键词： 频率一致纠缠 Hong-Ou-Mandel干涉测量 符合计数     

去甲基构树宁B的合成

以1,3-二羟基苯和对羟基苯甲醛为起始原料,经赫氏酰化、羟基保护、克莱森 斯密特缩合及催化氢化反应首次合成天然产物去甲基构树宁B,总收率40.9%,其结构经¹H NMR, ¹³C NMR和HR-MS(ESI TOF)确证。     

Measurement of the carrier recovery time in SOA based on four-wave mixing on narrow-band ASE spectrum

Carrier recovery time is a key parameter that determines the performance of a semiconductor optical amplifier (SOA). A measurement method of carrier recovery time in SOA based on a nearly degenerate four-wave mixing of narrow-band amplified spontaneous emission (ASE) spectra is presented. The results show the carrier times are 50.2, 44.6, and 23.6 ps when the injected currents are 120, 180, and 240 mA, respectively, which are in agreement with the nominal values of the sample.     

Microparticle collection for water purification based on laser-induced convection

Water purification is required for environmental protection. In this paper, we propose and demonstrate a rapid, effective and low-cost approach to collect numerous impurities(microparticles) in water on the basis of laser-induced thermal convection. We introduce a heat source by using a fiber tip, which is fabricated into a non-adiabatic-tapered shape. In order to improve the laser power absorption efficiency, we coat a gold film with a thickness of 300 nm on the fiber tip. Due to absorption, the laser power transferred from the fiber to the water results in thermal convection. The forces generated from the thermal convection drive the microparticles to move towards the fiber tip, thereby performing microparticle collection and achieving water purification. Laser-induced thermal convection provides a simple, high-efficiency and low-cost method of collecting microparticles, which is a suitable and convenient for local water purification.