利用光子相关光谱测量流体加速度——一种新的流体加速度计

推导了伴有布朗扩散运动的匀加速运动流体的外差光子相关光谱强度,论证了外差光子相关光谱强度的振荡频率与扩散运动及入射激光光场强度无关。基于这个理论结果提出了一     

Microwave frequency shifting using photon acceleration

Using a Bostick Gun as a plasma source, we have been investigating the effects of a moving plasma front on the frequency of an incident R.F. signal. We have been able to measure frequency shifts of 10 MHz frequency with a 2.6 GHz signal. The density is such that the plasma frequency is well above the transmitter frequency 1.3 meters from the plasma source. No magnetic field is used.     

用光子回波技术测量物质的横向弛豫时间

本文采用密度矩阵法推导光子回波讯号强度与激光光脉冲相对延迟的一般关系,得出二脉冲、三脉冲光子回波强度随时延的变化公式。实验上,用可调谐染料激光器作为光源,分别采用二脉冲、三脉冲光子回波技术,测得室温常压下饱和碘蒸气的横向弛豫时间T2约为140ps。     

Doppler and acceleration tolerances of high-gain, wideband linear FM correlation sonars

An analysis is presented of the decorrelation effects of target velocity and acceleration on high-gain, wideband linear FM correlation sonars that match the received signal against a family of velocity reference functions, each of which is a different time-compressed or -expanded replica of the transmitted signal. Such sonars are shown to have velocity (i.e., Doppler) and acceleration tolerances far different from that predicted by narrowband radar theory. Unlike the narrowband case, the wideband velocity tolerance may be quite small and is approximately independent of the carrier frequency and inversely proportional to the time-bandwidth product (TW). Narrowband radar-type calculations of velocity tolerance can give erroneous results far in excess of the true value. This is because the narrowband velocity tolerance is derived entirely on the basis of temporal overlap loss, whereas the actual tolerance depends primarily on the slope difference between the frequency-time sweeps of the received and reference signals. High acceleration tolerance, without separate acceleration processing channels, can be achieved by cross-correlating the acceleration return with a "best match" velocity reference function. The resultant wideband acceleration tolerance is approximately inversely proportional to WT²and better than the narrowband tolerance by a factor of 12 Q (Q = carrier frequency/bandwidth). This improvement arises because the wideband reference functions are able to partially compensate for the nonlinearity imparted to the transmitted frequency-time sweep by an accelerating target, whereas such compensation is not possible in narrowband systems employing carrier-shifted reference functions.     

基于相关系数的证据冲突度量方法

当证据高度冲突时,使用D-S组合规则将会得到不合常理的结果,因此,针对证据组合规则的改进成为一个重要的研究课题,在选择合适的证据组合方法之前,确定证据之间是否冲突、冲突程度如何,是个至关重要的问题,为了更加准确地描述证据间的冲突,在分析证据相似度与证据冲突关系的基础上,基于证据相关系数提出了一种新的证据冲突度量方法,理论分析和数值计算表明该方法可有效表示证据之间的冲突程度,相关系数越大,证据间冲突就越小,与其他方法相比,该方法更具全面性和合理性。     

Molecular photodissociation by an ultraviolet photon

The laser has greatly expanded the study of photodissociation dynamics. By generating large concentrations of fragments using monochromatic light, the laser enables the measurement of their final state distribution. This distribution over translational, vibrational, and rotational states combined with the conservation of energy and linear and angular momentum allows us, in principle, to calculate the forces acting in the excited state. A review of experimental results so far obtained shows that: 1) for diatomics the quantum states of the dissociated atoms can now be directly determined, 2) for triatomics the excess of photon energy over dissociation energy appears in comparable amounts in vibrational and translational energy with rotational energy often substantial as well (ICN and H2S are exceptions), 3) in complex molecules optical energy is absorbed in one part of the molecule and utilized in another with resulting intramolecular transfer of energy.     

基于激光散斑角度相关法表面粗糙度测量

为了完成对精密机械表面粗糙度的精确测量,基于远场角度散斑强度的相关理论,采用激光散斑方法设计了表面粗糙度测量的实验光路。在实验光路中,将平面镜与待测粗糙表面固锁在一起,当转动待测粗糙表面时,平面镜与分束镜、接收屏组成了测量转动角度的光指针,提高了转动角度的测量准确度。在数据处理中,提出了基于MATLAB软件的角度散斑相关度峰值的计算方法,简化了测量步骤,提高了测量速度,进而利用相关度峰值计算求得表面粗糙度。利用设计和组建的系统对平铣表面粗糙度标准模块的表面粗糙度进行了实际测量,并对测量结果与标准样块的标称值进行比较,取得了较高的测量准确度。结果表明,此研究验证了激光散斑方法测量表面粗糙度的可行性,对进一步完善表面粗糙度的精密测量是有帮助的。     

超短脉冲激光特性的三阶相关测量研究

在飞秒激光放大系统研制以及激光与物质相互作用研究过程中,良好的脉冲对比度是十分重要的一个指标,为了准确地测定激光对比度,我们利用非线性晶体对激光强度变化十分敏感的特性,研制了一台三阶相关仪,并对一台飞秒激光器进行了脉冲对比度的测量研究,所得结果揭示出了二阶相关仪所无法得到的信息,为测量飞秒激光脉冲的对比度提供了一种简便的方法.     

Optical time domain reflectometry by photon counting

A photon counting technique has been used to extend greatly the range of optical time domain reflectometry or `back-scatter? for fault location in optical fibre systems. A range of more than 40 dB of one-way fibre loss has been achieved even when the break was index-matched to eliminate any reflection.     

Generation of optical vortices by apodized photon sieves

As a novel diffractive optical element, photon sieve has good focusing properties. We propose a method to verify the focusing properties by using apodized photon sieves. The apodized photon sieve is obtained by using a Gaussian window function to modulate the general photon sieve. Focusing properties of apodized photon sieve are studied by numerical simulations and experiments. It shows that photon sieves have good focusing ability, and the focusing ability of the photon sieve on the focal plane is stronger than that on other image planes. The experimental results also demonstrate that photon sieves can be used to generate optical vortices. The existence of optical vortices is confirmed by the formation of fork fringes. This apodized photon sieve is expected to have some practical applications in focusing analysis, optical imaging, and optical communication.     

加速寿命试验中修正阿伦尼斯加速因子的研究

阿伦尼斯(Arrhenius)加速因子常用于可靠性加速寿命试验(ALT)或环境应力筛选(ESS)的温度应力加速寿命模型中,但事实上Arrhenius方程和由其得出的Arrhenius加速因子之间存在着矛盾.本文首先提出这一矛盾,接着从激活能的定义及物理意义进行分析,说明了引起矛盾的原因,并最终得出修正Ar-rhenius加速因子.