调频连续波分布式光纤布拉格光栅复用系统

研究了利用调频连续波(FMCW)技术对分布式光纤布拉格光栅(FBG)复用系统进行寻址的基本原理;仿真分析了FBG传感器复用距离是系统最小分辨距离的整数倍或非整数倍时,对频谱信号的影响;搭建了基于FMCW的FBG复用系统实验平台,当传感距离1000m时,分别验证了不同扫描周期与复用系统差频信号的线性关系,及不同扫频范围与系统差频信号的线性关系。实验结果表明:FBG复用距离是系统最小分辨距离整数倍时,在测量距离1100 m范围内,系统测量最大误差为243 Hz,最大相对误差小于5%,可以实现FBG传感器的地址查询功能。     

快速扫描频率分辨光学开关装置测量超短激光脉冲

频率分辨光学开关法是目前测量超短激光脉冲的主流方法之一.本文比较了三大类二次谐波频率分辨光学开关系统的特点和适用范围,提出将标准二次谐波频率分辨光学开关法改装成一种快速扫描频率分辨光学开关法(frequency-resolved optical gating, FROG)装置.利用信号发生器输出的正弦信号同步地驱动音圈电机和扫描振镜,其中音圈电机带动直角反射镜往复运动可实现快速的延时扫描,与此同时扫描振镜快速转动进而按照延时顺序将自相关信号光谱反射至面阵相机感光面上的不同位置.该正弦信号还用于触发面阵相机持续曝光,即可拍摄到一幅完整的FROG迹线图,曝光时间可小于1 s.该方案在需要记录较大矩阵FROG迹线图的情形颇具优势,例如可实现色散大的啁啾脉冲和结构复杂的超短脉冲的实时测量.通过测量从自锁模钛宝石激光器输出的飞秒脉冲以及被200 mm厚的BK7玻璃块展宽后的啁啾脉冲的结构,证实了该装置的实用性.     

FPGA高精度测量频率研究

广播载波频率的精确测量是检测载波频率是否稳定的重要手段。由于常规测量频率的方法存在频率测量前后沿不确定性的问题,使测量结果存在1个字的测量误差。提出了全同步测频法测频,实现了被测信号、标准信号和闸门信号三者同步,从而消除了标准信号的1个字的量化误差。用VHDL语言编写了测频程序,在FPGA(现场可编程门阵列)上实现计数和控制,将测量数据通过串行线送到ARM微处理器上计算并显示出来,实现了四路中波载波的频率精确测量。     

重复频率倍增光频梳时域互相关绝对测距

利用法布里-珀罗标准具对光纤光频梳的重复频率(重频)进行倍增,使光频梳重频从最初的250 MHz提升至10 GHz,对应的脉冲间距从1200 mm缩减至30 mm,极大地降低了脉冲互相关测距方法对参考臂扫描范围的需求.建立了重频倍增光频梳的时域互相关干涉信号数学模型,通过数值模拟分析了光源参数(重频、起始偏移频率)和法布里-珀罗标准具参数(色散、腔长、中心波长)对滤出光谱形状以及互相关信号的影响.在实验中,使用重频倍增后的光频梳进行脉冲互相关干涉绝对测距,与参考干涉仪对比,在210 mm范围内获得优于4μm的测距精度.     

正、负电子贮存环与其入射器加速频率的关系

本文分析了e^－e⁺电子贮存环与其入射器加速频率是否要成整数倍关系的问题. 特别在近年来, 次谐波聚束器提出以后, 这个问题更为突出. 文中对此问题从几方面来进行讨论, 最后提出了两个新的建议, 使两者频率可以不保持整数倍关系, 但又具有频率成整数倍时的优点.     

基于双弹光差频调制的中红外波片相位延迟高精度测量

提出了一种基于双弹光差频调制的中红外相位延迟精确测量方法。通过两个硒化锌型弹光调制器(PEM)的差频降低系统调制频率,产生载有被测相位延迟的低频调制信号,调制后的1倍差频幅值和2倍差频幅值相除可求得被测波片的相位延迟。该方法可有效抑制光强波动及PEM相位延迟波动对测量的影响,提高测量精度。对测量原理进行了理论推导,设计了硒化锌型PEM和实验系统。实验结果表明,相位延迟测量误差不大于0.004%,灵敏度可达5×10~(-4) rad。     

数字相位测距仪信号源的研究与设计

在相位激光测距仪中,信号初始相位的相对稳定性对测距仪的测量精度非常重要.对于如何得到全同步的主振信号、本振信号、差频参考信号以及填充脉冲,给出了采用单片机控制频率合成器(DDS)直接数字频率合成芯片,直接滤波以及FPGA软件模拟DDS原理三种不同的方案,最后对这三种方案进行了比较.直接滤波法实现起来简单且成本较低,适合测量精度不是很高的系统.另外两种方案可用于测量精度较高的系统,但是成本较高.     

利用光纤和变频方法测量光速

对导入一分为二光纤的激光进行强度调制,改变其调制频率,经光电转换后送入示波器监测X-Y合成的李萨茹图形,使两路激光输出信号相位差为2π整数倍.利用调制频率和光程差即可计算出光速.     

光栅外腔半导体激光器GHz射频调制特性研究

研究了光栅外腔半导体激光器(ECDL)对射频频率调制的响应特性,分析了射频频率调制时光栅外腔对半导体激光器的边带信号的影响.实验中测量了GHz射频频率调制的.ECDL输出的边带信号随射频信号功率、注入电流、光栅外腔长度的变化情况.证实了当射频调制频率等于光栅外腔自由光谱区的整数倍时,ECDL输出的边带信号可在一定程度上得到增强.     

三能级原子与少周期脉冲串作用中的相干布居捕获

研究了少周期脉冲串作用下三能级原子中的布居转移和相干布居捕获现象.在非旋波近似的情况下求解了密度矩阵方程.研究结果表明在等时间间隔的锁相脉冲作用下,系统能级的布居逐步转移并积累,系统基态相干也逐步积累.在满足脉冲重复频率为基态能级频差的整数分之一倍时,三能级系统和频率梳中两梳齿频率成分作用形成相干布居捕获现象,原子暗态布居值达到最大,介质对脉冲透明.在适当选取少周期脉冲参量的情况下,在0.5个ns的时间内三能级系统相干性演化到最大后到达稳态,相干布居捕获发生.与脉宽为100个fs的多周期脉冲相比,少周期脉冲串在介质中建立相干布居捕获的时间缩短两个数量级.由于频率梳中与三能级系统发生作用的梳频成份有相同的频移,相干布居捕获的条件双光子共振仍然满足.因而,当两基态能级频率差较大时,如果选取少周期脉冲载波频率为系统能级1至2和1至3的传输频率之和的一半ω=(ω₁+ω₂)/2,室温下原子热运动的引起的多普勒频移并不会破坏相干布居捕获.     

变像管同步扫描相机的理论分析

本文主要讨论了变像管同步扫描对皮秒弱光现象诊断理论依据,从噪声理论出发,导出了这种相机的探测方程和最小可探测光功率密度的表达式,同时用概率论和数理统计的方法研究了这种相机的极限时间分辨率,并用蒙特卡洛模拟方法计算了其时间传递函数。分析表明,该类相机的最小可探测光功率密度约为10¹²W/mm,时间分辨率较单次扫描机更高。     

一种新型皮秒同步扫描变像管

本文描述了一种新型皮秒同步扫描变像管的设计特点及实验结果。其静态空间分辨率为50lp/mm,时间分辨率为1.1ps。     

B. 变像管诊断技术

本文评述了变像管诊断技术的国内外最新发展,详细地分析介绍了本届会议上出现的几种新管型,并涉及到某些应用。     

扫描相机标定脉冲信号位置的确定及噪声处理

 扫描相机标定数据处理中的一个关键问题是如何准确确定脉冲信号的位置，实验数据的信噪比和脉冲信号位置的定义方法都会对标定结果的准确性产生影响。采用了取半高宽的方法来确定扫描相机标定脉冲信号的位置，在信噪比比较高 （大于100） 的情况下，该方法确定标定信号的位置可以达到亚像素水平。对于信噪比比较低 (小于10) 的实验数据，先采用快速傅里叶变换方法对其进行滤波，通过滤波可以极大地抑制噪声信号的影响，然后采用“半高宽法”确定脉冲信号的位置，最后得出可信的标定结果。当扫描相机定在0.3 ns的扫描档时，通过该方法得到的扫描速度为0.214 ps/pixel,扫描不确定度为0.002 9 ps/pixel,拟合线性相关系数为0.999 7。     

基于电子轰击式CCD的大动态条纹相机研究

为了实现对更弱、以及物理量跨度更大的信号探测, 满足材料、生物、信息、半导体物理以及能源等重大科学领域对诊断精密化的进一步需求, 需要提高条纹相机的动态范围、空间分辨率和信噪比. 为此, 本文研制了基于电子轰击式CCD(EBCCD)的大动态条纹相机, 条纹变像管采用时间和空间方向分别聚焦的矩形框电极和电四极透镜结构, 可降低空间电荷效应. 并提高电子加速电压, 减小电子渡越时间以降低空间电荷相互作用时间. 采用基于电子轰击读出技术的背照式CCD(BCCD)作为读出器件, 取代传统的像增强CCD(ICCD)以缩短图像转换链, 较大地降低了超快诊断设备转换过程中的图像衰减, 从而提高条纹相机图像的信噪比、空间分辨率和动态范围. 实验得到静态空间分辨率高于35 lp/mm, 动态空间分辨率达到20 lp/mm, 偏转灵敏度为60.76 mm/kV, 动态范围达到2094:1, 扫描速度非线性为5.04%, 条纹相机的电子轰击半导体(EBS)增益达到3000以上.     

Improving the precision of fluorescence lifetime measurement using a streak camera

Streak camera has high temporal resolution and high sensitivity, and is a powerful tool in biomedical study to measure fluorescence lifetime and perform fluorescence lifetime imaging. However, nonuniformity of the gain in the streak tube and nonlinearity of the sweeping speed limit the precision of fluorescence lifetime measurement, particularly when fluorescence lifetimes are short. We have constructed a two-photon excitation fluorescence lifetime measurement system that is based on a synchroscan streak camera and have developed accordingly a method to correct the effect of gain nonuniformity and nonlinearity of sweeping speed on the measurement precision. A continuous-wave laser of high stability is used to calibrate the gain of the streak camera, and a Fabry-Perot etalon is used to calibrate the nonlinearity of the sweeping speed. Fitting algorithms are used to correct the gain of the streak camera and nonlinearity of the sweeping speed respectively, which significantly improves the measurement precision of the system, as characterized through the fluorescence lifetime of the short-lived fluorescence dye, Rose Bengal. Experimental results show that the measurement fluctuation of the lifetime has been improved from more than 10% to 2% after correcting the effects of gain nonuniformity and sweeping speed nonlinearity.     

Sound localization in noise in normal-hearing listeners

The ability to localize a click train in the frontal-horizontal plane was measured in quiet and in the presence of a white-noise masker. The experiment tested the effects of signal frequency, signal-to-noise ratio (S/N), and masker location. Clicks were low-pass filtered at 11 kHz in the broadband condition, low-pass filtered at 1.6 kHz in the low-pass condition, and bandpass filtered between 1.6 and 11 kHz in the high-pass condition. The masker was presented at either -90, 0, or +90 deg azimuth. Six signal-to-noise ratios were used, ranging from -9 to +18 dB. Results obtained with four normal-hearing listeners show that (1) for all masker locations and filtering conditions, localization accuracy remains unaffected by noise until 0-6 dB S/N and decreases at more adverse signal-to-noise ratios, (2) for all filtering conditions and at low signal-to-noise ratios, the effect of noise is greater when noise is presented at +/- 90 deg azimuth than at 0 deg azimuth, (3) the effect of noise is similar for all filtering conditions when noise is presented at 0 deg azimuth, and (4) when noise is presented at +/- 90 deg azimuth, the effect of noise is similar for the broadband and high-pass conditions, but greater for the low-pass condition. These results suggest that the low- and high-frequency cues used to localize sounds are equally affected when noise is presented at 0 deg azimuth. However, low-frequency cues are less resistant to noise than high-frequency cues when noise is presented at +/- 90 deg azimuth. When both low- and high-frequency cues are available, listeners base their decision on the cues providing the most accurate estimation of the direction of the sound source (high-frequency cues). Parallel measures of click detectability suggest that the poorer localization accuracy observed when noise is at +/- 90 deg azimuth may be caused by a reduction in the detectability of the signal at the ear ipsilateral to the noise.     

Picosecond‐resolved X‐ray absorption spectroscopy at low signal contrast using a hard X‐ray streak camera

A picosecond‐resolving hard‐X‐ray streak camera has been in operation for several years at Sector 7 of the Advanced Photon Source (APS). Several upgrades have been implemented over the past few years to optimize integration into the beamline, reduce the timing jitter, and improve the signal‐to‐noise ratio. These include the development of X‐ray optics for focusing the X‐rays into the sample and the entrance slit of the streak camera, and measures to minimize the amount of laser light needed to generate the deflection‐voltage ramp. For the latter, the photoconductive switch generating the deflection ramp was replaced with microwave power electronics. With these, the streak camera operates routinely at 88 MHz repetition rate, thus making it compatible with all of the APS fill patterns including use of all the X‐rays in the 324‐bunch mode. Sample data are shown to demonstrate the performance.     

A new synchroscan streak-camera read-out system for use with CW mode-locked lasers

The synchroscan streak-camera system has been further developed to obtain both picosecond temporal resolution and direct photomultiplier read-out from a single image tube. Advantages include reduction in cost, potentially improved S/N ratio, greater dynamic range and “free temporal range”, and ultimately improved time-resolution in the subpicosecond regime. An application to signal-to-noise improvement in Raman spectroscopy is described.     

大动态范围飞秒扫描变象管理论设计与实验评价

设计了一种具有大动态范围的多用途飞秒扫描变象管,其理论时间分辨率可达50fs.分别借助掺钛蓝宝石飞秒激光器和YAG皮秒激光器对其性能进行了实验评价.获得了同步工作状态下时间分辨率1.8ps以及单次扫描工作状态下动态范围优于128:1的结果.