LiNbO_3:Fe晶体中光感应四波混频光散射

本文报道用一束异常氩激光倾斜照射LiNbO_3:Fe晶体薄片时出现的两种新的光感应光散射现象,讨论了它们的产生机理。     

光折晶体Fe:LiNbO_3中的光致散射效应

本文给出了光折晶体中光致散射理论,并用Fe:LiNbO_3晶体以氩离子激光为光源研究了光致散射效应,得到了透射光强度随照射时间变化的动态曲线及与理论一致的散射光强随散射角变化的实验曲线.实验中还观察到表面复合效应,提供了简便地消除此效应的方法.     

新型光折变晶体Ce:BSO中的各向异性光散射

各向异性光散射现象已在几种光折变晶体中观察到,如BaTiO_3,Fe:LiNbO_3,Cu:LiTaO_3。这几种晶体共同特点是均具有较高的光折变灵敏度,因而晶体中缺陷引起的杂散光与入射光相互作用时能够得到放大,产生各向异性光散射。普通BSO(Bi_(12)SiO_(20))晶体光折变灵敏度较低,未发现各向异性散射现象。我们在首次生长的新型光折变晶体Ce:BSO中观察到一种新的很强的各向异性光散射,并利用BSO晶体的光折变理论给予较圆满的解释。     

光折变晶体全息存储中散射噪声特性的研究

采用信噪比损失系数 (LSNR)深入研究了光折变铌酸锂晶体中散射噪声对全息输入图像像质的影响。对不同掺杂物质、不同掺杂浓度、不同处理方法以及不同记录方式的大量晶体进行了实验研究 ,并重点考察了物光束引起的散射噪声的特性。实验结果表明 ,氧化态晶体的散射噪声的影响小于生长态和还原态晶体 ,反射光路较之透射光路和邻面入射 ( 90°)光路更不易受散射噪音影响     

1.8～2.5微米可调谐LiNbO_3光参量振荡器

报导一种用重复频率1次/秒,双45°LN电光调Q,Nd:YAG一级振荡二级放大,输出e偏振1.064微米激光做泵浦源,实现双谐振温度调谐的LiNbO_3光参量振荡器。泵浦激光脉宽30毫微秒,输出能量在120毫焦耳左右。用掺1％MgO:LiNbO_3做参量晶体,以相位匹配角Q=49°切割。参量振荡腔采用平面腔结构,宽带腔片在1.8～2.5微米范围内高反,1.064微米T≥90％。整个参量腔放入200℃左右可调的恒温槽中,恒温精度±0.2℃。参量振荡输出波长由一     

同步加速器辐射产生飞秒辐射脉冲

劳伦斯·伯克利国家实验室的研究人员已产生持续不足 30 0 fs的频闪式同步加速器闪光。这些亚皮秒脉冲的光谱范围从红外延伸至 X射线波长。在伯克利实验室的高级光源 ( ALS) ,研究者可直接从同步辐射加速器储存环的电子束中提取飞秒脉冲辐射。从 AL S直线加速器中产生 ( 50 Me V)的相对论电子脉冲与红外激光产生的 10 0 fs脉冲交叉成 90°角。在这种布局中 ,部分红外光子与电子相互作用并被散射。散射光子具有 X射线的能量 ,沿与电子束相同的方向传播 ;离散射脉冲中心最近的光子具有最高的能量。散射脉冲的弛豫时间由红外脉冲通过电子束…     

LiNbO_3：Fe中的两种光折变机制

ＬｉＮｂＯ_３：Ｆｅ中的两种光折变机制郭儒，凌振芳，刘思敏，张光寅（南开大学物理系，天律３０００７１）实验指出，将一束会聚的激光照射在掺铁的铌酸锂（０．０８ｗｔ％Ｃ切割的晶体表面时，有两种不同的光感应光散射现象。当人射光滑方向入射时，只形成一般的背向?..     

人血管对He-Ne激光的吸收系数和散射相函数的研究

运用光生物学、基础医学以及物理学的基本理论,探讨了人血管组织的激光传播特性,定量测定了人血管组织的激光传输参量。采用标准积分球测量了人血管组织样品在632.8nmHeNe激光照射下的透射比T和反射比R,推算吸收比A。并把分光仪改装为光散射测量装置,测量了632.8nmHeNe激光照射下,-90°～90°散射角范围内的散射相函数S(θ),计算散射余弦平均值μ。结果表明:人血管组织受小功率(P=20mW)632.8nmHeNe激光照射时,光强衰减符合指数衰减规律,人血管组织对激光有较弱的前向散射。     

专利

美国加州的Kafka J D等人提出一种新颖的同步泵浦光学参量振荡器设计方案.该参量振荡器是由一个带有光路的共振腔、高功率泵浦光源和温度控制系统组成.在共振腔光路中的光束腰位置放置LBO晶体.高功率泵浦源产生波长为700nm～900nm的亚 皮秒脉冲光辐照LBO晶体,选择共振腔长度 使泵浦源实现同步泵浦的工作条件.温度控制系统控制LBO晶体的温度在2°C左右.(美国专利号:5847861)(No.66)高效单频变换仪美国康涅狄洛州Zygo公司的Hill H A发明一种光电变频仪.该仪器可把单频线偏振激光束转换成具有一对共线垂直偏振分量的光束,每一个分量有一个不同的频率.电子系统频率为f_o的电信号,与电信号连接的声—光器件用于调节与入射光束相关的出射光束的强度,从而使单频线性偏振激光束转换成具有高衍射效率的双共线垂直偏振分量的激光束.     

用于大功率激光焊接的组合YAG激光器

日本AMAGASAKI消息,目前工业生产厂商正在寻找一种用于焊接厚金属板的高亮度、大能量的YAG激光器,日本的科研人员正试图满足这一需要.先进材料处理研究所Shigek Fujinaga领导的研究组利用组合YAG激光束获得高平均功率,并将其用于厚金属板的焊接.该研究组研究出两种组合YAG激光束的方法,两种方法均采用光纤传输能量.一种方法是在出射端组合光束,而另一种是在入射端.研究人员利用两束,且每束具有2kw平均功率的CW(连续波)YAG激光束和一束1.5 kw功率的脉冲激发光束,实验测定了能产生5.5 kW平均功率的激光束焊接的各种特性.Fujinaga说:“两种光束组合方法各具优点和缺点,……在光纤的出射端使用集束光学组件的一个缺点是,对焊接机器人来说,显得太大、太重以致于不能快速移动,而在光纤的入射端组合激光束的缺点是,它排除掉了三条光束中任何非聚焦的光束,当把两条CW YAG光束和一条脉冲激发光束组合时,发现有时还需要做点什么才行.”为了确定最佳空间配置,研究人员发现,当光束对工件表面法线的人射角呈15°时,火舌卷流(Plume)的形态和焊接深度是个常数.把入射角增加到30°会导致熔深分叉,并在焊缝截面方向上使熔化面积扩大.但是利用集束光学组件组合时,他们发现,在水平焊接时,虽然未出现熔深分叉,也不必将光     

Equivalent transformations for the mixed lumped Brune-type sectionand uniform transmission line

As an analytical method for nonuniform transmission lines (NTLs) equivalent transformations are extended to a more general case, namely a mixed lumped Brune-type section and a uniform transmission line (unit element, UE). Circuits consisting of a cascade connection of a lumped Brune section and a UE are equivalent to one consisting of a cascade connection of a nonuniform transmission line whose characteristic impedance distribution is expressed with a trigonometric function and a lumped Brune section. This equivalent transformation method is easily applied to a circuit consisting of a lumped C section and a UE. The equivalent circuit is a circuit consisting of an NTL and a lumped C section. In this case, the characteristic impedance distribution of the NTL may be expressed in terms of a hyperbolic function. Exact network functions of the NTLs are easily obtained from the equivalent circuits without solving the telegrapher's equation. By considering the limiting case of these equivalent transformations, equivalent transformations for circuits consisting of a cascade connection of a lumped resonance circuit and a circuit and a uniform transmission line are derived     

Filter-embedded design and its applications to passive components

A design in which a filter is embedded in a fiber fixed on a substrate is proposed. It was successfully applied to the fabrication of low loss fiber optic components for a single-mode fiber transmission system. These components have a wide operational temperature range. The design is easily adapted to a multifilter or multifiber component. Filter embedding is achieved in two ways. One is to insert a thin filter chip in a slit which is machined into a fiber fixed on a substrate by a dicing saw (filter inserted type). The other is to evaporate a filter film directly on a fiber end face and butt this fiber to another fiber on a guide groove on a substrate (filter evaporated type)     

Some Theoretic Results on a Digital EMG Signal Processor

As is well known, a general EMG signal processing scheme includes a prewhitening filter, a v-order detector, a smoothing filter, and a relinearizer. In this paper, a theoretical analysis of such a scheme is carried out, including a detector characteristic which presents a logarithmic behavior.     

Unifying probabilistic and variational estimation

A maximum a posteriori (MAP) estimator using a Markov or a maximum entropy random field model for a prior distribution may be viewed as a minimizer of a variational problem.Using notions from robust statistics, a variational filter referred to as a Huber gradient descent flow is proposed. It is a result of optimizing a Huber functional subject to some noise constraints and takes a hybrid form of a total variation diffusion for large gradient magnitudes and of a linear diffusion for small gradient magnitudes. Using the gained insight, and as a further extension, we propose an information-theoretic gradient descent flow which is a result of minimizing a functional that is a hybrid between a negentropy variational integral and a total variation. Illustrating examples demonstrate a much improved performance of the approach in the presence of Gaussian and heavy tailed noise. In this article, we present a variational approach to MAP estimation with a more qualitative and tutorial emphasis. The key idea behind this approach is to use geometric insight in helping construct regularizing functionals and avoiding a subjective choice of a prior in MAP estimation. Using tools from robust statistics and information theory, we show that we can extend this strategy and develop two gradient descent flows for image denoising with a demonstrated performance.     

High-speed sensory-motor fusion based on dynamics matching

This paper discusses a design concept of a sensory-motor fusion system to achieve high performance in a dynamic changing environment. From the viewpoint of a dynamic system, the new concept called "dynamics matching" is proposed to match the dynamics constraints of a system. Based on this concept, we describe a high-speed vision chip that has a general purpose parallel processing array along with a photodetector all in a single silicon chip. Next we describe a new sensory-motor fusion system which consists of a hierarchical parallel processing system, a vision chip system, and a multifingered hand-arm. All sensory feedback, including visual feedback, can be achieved in 1 ms. In addition, as an application of the system, we demonstrate high-speed grasping using visual and force feedback.     

Stereo‐Vision‐Based Human‐Computer Interaction with Tactile Stimulation

If a virtual object in a virtual environment represented by a stereo vision system could be touched by a user with some tactile feeling on his/her fingertip, the sense of reality would be heightened. To create a visual impression as if the user were directly pointing to a desired point on a virtual object with his/her own finger, we need to align virtual space coordinates and physical space coordinates. Also, if there is no tactile feeling when the user touches a virtual object, the virtual object would seem to be a ghost. Therefore, a haptic interface device is required to give some tactile sensation to the user. We have constructed such a human‐computer interaction system in the form of a simple virtual reality game using a stereo vision system, a vibro‐tactile device module, and two position/orientation sensors.     

A Note on Loaded Line Synthesis (Correspondence)

The purpose of this note is to present an alternate derivation of a formula for the synthesis of a loaded line. The problem is to determine the values of the normalized susceptances a and c mounted an exact quarter-wavelength apart along a uniform line. These are arranged in the order a, c, c,. . .c, a to achieve a loaded line with a given phase shift and perfect match. In order to analyze a particular line design for standing-wave ratio and phase shift over a band of frequencies on a digital computer, it is worthwhile to know the values of the susceptances to many more decimal places than one would achieve from a simple graph.     

A W-Band Air-Cavity Filter Integrated on a Thin-Film Substrate

In this letter, a W-band air-cavity filter has been developed on a thin-film substrate using a lossy silicon substrate as a base plate, which is suitable for a mm-wave system-on-package. The lossy silicon suppresses a parasitic substrate mode excited in a thin-film substrate, while a coupling loss between a transmission line and a resonator is minimized by etching the backside of the lossy silicon substrate underneath the coupling area. In the backside etching process, 70 mum of silicon was left for mechanical support of the thin-film substrate. The resonator was fabricated using a low-cost silicon micromachining technique and was flip-chip integrated on a thin-film substrate. The fabricated air-cavity resonator showed an unloaded Q of 851 at a resonant frequency of 94.18 GHz. Improvement in the coupling loss by the backside etching process was verified with measurement results. The fabricated filter exhibited an insertion loss of 1.75 dB and a return loss better than 14.5 dB with a 1.3% 3 dB fractional bandwidth at a center frequency of 93.8 GHz.     

Remote-controlled platoon merging via coder-estimator sequence algorithm for a communication network

In this paper, a platoon-merging control system is considered as a remotely located system with a state represented by a stochastic process. In this system, it is common to encounter situations where a single decision maker controls a large number of subsystems, and observation and control signals are sent over a communication channel with finite capacity and significant transmission delays. Unlike a classical estimation problem where the observation is a continuous process corrupted by additive noise, there is a constraint that the observation must be coded and transmitted over a digital communication channel with finite capacity. A recursive coder-estimator sequence is a state estimation scheme based on observations transmitted with finite communication capacity constraint. In this paper, we introduce a stochastic model for the lead vehicle in a platoon of vehicles in a lane considering the angle between the road surface and a horizontal plane as a stochastic process. In order to merge two platoons, the lead vehicle of the following platoon is controlled by a remote control station. Using the coder-estimator sequence, the remote control station designs the feedback controller. The simulation results show that the inter-vehicle distance and the deviation from the desired inter-vehicle distance are well regulated.     

Distortion Compensation of Reconstructed Hologram Image in Digital Holographic Display Based on Viewing Window

A holographic display based on a viewing window enables the converging of a reconstruction wave into a viewing window by means of an optical system. Accordingly, a user can observe a reconstructed hologram image, even with a small diffraction angle. It is very difficult to manufacture an optical system with no aberrations; thus, it is inevitable that a certain amount of wave aberrations will exist. A viewing‐window‐based holographic display, therefore, always includes distortions in an image reconstructed from a hologram pattern. Compensating the distortions of a reconstructed image is a very important technical issue because it can dramatically improve the performance when reconstructing a digital three‐dimensional content image from a hologram pattern. We therefore propose a method for suppressing image distortion by measuring and compensating the wave aberration calculated from a Zernike polynomial, which can represent arbitrary wave aberrations. Through our experimental configuration using only numerical calculations, our proposed method decreased the reconstructed image distortion by more than 28%.