两维相干度调制光波的解调

本文从理论上推出,利用Raman-Nath型声光调制器和两维光栅,即可进行光波空间相干度的两维调制与解调,从而实现信号的双路传输,实现光波的波面复用.对两维行波型调制情况进行了实验验证.     

基模高斯光束轴向相干叠加柱波场的研究

运用标量光学理论,研究了纳米加工中的基模高斯光束轴向相干叠加光场的三维强度分布特征,导出了高斯驻波场的光强分布表达式。在此基础上通过数值计算方法,分析比较了正确波驻波场与高斯驻波场之间的异同点。     

原子纳米光刻中双层光学掩膜的实现方法研究

利用原子光刻的方法制备纳米结构的光栅已经成为了一种较为成熟的工艺。通过原子与激光驻波场的相互作用,利用原子自生在势能场中的偶极力对原子的密度进行调制,从而得到所需要的光栅结构。利用此种工艺所制备的光栅相对于传统工艺来说具有精度高,光栅常数直接溯源于原子能级。希望能够通过对激光的改良来提升原子沉积结果。通过双层驻波场来提高原子沉积质量已经被多次提到。实验中利用几何光学的方法实现了所需要的新型激光驻波场。并对其汇聚,相干等特性进行了研究,取得了较为满意的结果。为利用双层驻波场来沉积原子打下了基础。     

调制相干度的光波的解调

本文提出一种调制空间相干度光波解调的概念,理论分析及相应的实验结果表明,这种调制波及其解调在相干光通信中可能将有实际意义。     

基于Bose-Einstein凝聚腔光力学系统的可调控相干完美吸收

研究了基于Bose-Einstein凝聚(BEC)腔光力学系统中的相干完美吸收现象,阐述了诱导相干完美吸收产生的条件,分析了强耦合BEC光力学腔发生相干完美吸收时的能量转换.通过控制泵浦场功率可以有效调制相干完美吸收.当相干完美吸收产生时,输入探测场能量完全转化为机械振子和腔场能量而不产生任何透射和反射,并且通过改变腔的品质因子可实现能量萃取.强耦合BEC腔光力学系统为基于相干完美吸收的换能器、调制器及光开关等潜在应用提供了理论基础.     

部分相干方形平顶电磁脉冲光束经相位调制透镜的聚焦特性

将稳态场的相干偏振统一理论应用于脉冲光束的研究。构建了部分相干方形平顶电磁脉冲光束,并推导出该光束经相位调制透镜后聚焦的交叉谱密度函数表达式。详细探讨了相位调制尺寸、调制深度、调制中心位置以及光束相关长度等对聚焦场光谱强度的影响。研究结果表明,局域相位调制会导致在聚焦场中产生另一光谱强度峰值,光束的相关参数和相位调制参数决定该光谱强度峰值大小,并在一定情况下使之发生移动。特别是当光源相关参数和相位调制参数处于某临界值时,会发生光谱强度峰值开关现象。同时发现,空间相关长度导致光束发生空间焦移,而脉冲时间相关长度导致光谱强度峰值在频率上的移动。     

驻波场中囚禁离子的Wigner-Yanase偏态信息

研究了驻波场中囚禁离子的Wigner-Yanase偏态信息并得到了其恢复周期,发现此周期与离子布居数反转的恢复时间相同.对解析解与数值模拟进行分析,发现Wigner-Yanase偏态信息的恢复时间随Lamb-Dicke 参数的增大而减小,随离子平均振动声子数的增大而增大;当离子质心从驻波场波节移向波腹时,Wigner-Yanase 偏态信息的恢复时间变长.从理论上证明了囚禁离子振动态处于相干态时离子初始偏态信息恒为1/2,分析了离子与驻波激光场之间的量子纠缠特性.     

激发态上钠原子的相干囚禁

对Ｖ型三能级原子系统与双激光场同时共振产生的能级相干效应进行了研究。计算了各能级上的粒子数分布，实验观测到在相干驻波场中的钠原子被囚禁在激发态上的现象。对比和分析有无干涉效应存在时３Ｓ１／２，Ｆ＝２态上布居数的变化情况。     

关于驻波声光调制器等效阻抗问题

本文从实验现象出发，以行波声光调制等效电阻抗的计算方法为基础，给出了驻波声光调制器的理论模型，进而分析推导出驻波声光调制 中介质对换能器电阻抗贡献大小；从而对驻波声光调制器的工作状态和最佳使用条件进行了分析讨论。     

J0相关径向偏振涡旋光束紧聚焦的空间相干特性

为了研究J₀相关径向偏振涡旋光束深聚焦的相干特性,采用矢量德拜理论和相干理论,对聚焦场在光轴和焦平面上的相干特性进行了理论分析和数值仿真,取得相干度表达式和模拟数据。结果表明,在焦点区域的纵向相干度不但随着拓扑荷数n的增加而增大,而且还随着相干参量或者数值孔径d_NA的增大而减小;在焦平面的横向相干度也随着拓扑荷数或者相干参量或者数值孔径的增大而减小; 当n≥5或者d_NA≤0.4时,纵向相干度在焦点附近约为1;这种相干度还存在相位异常点。这些研究结果对J₀相关矢量涡旋光束在许多领域的应用具有一定意义。     

Distributed fiber-optic stress-location measurement by arbitrary shaping of optical coherence function

A functional distributed fiber-optic stress-location measurement technique by arbitrary shaping of the optical coherence function has been demonstrated. The technique measures the distribution or location of stress-induced polarization mode coupling in a polarization-maintaining fiber by manipulating the optical coherence function. The location of applied stress is given by optical path difference between the two polarization modes, which is determined by the synthesis of the coherence function. Three types of coherence function-a scanning peak, a scanning low-sidelobe peak, and a standing triangle-have been synthesized experimentally and used for stress locating. When using the coherence function of scanning peak, the coherence peak is slid to scan over the measurement range by a phase modulation to obtain the stress distribution; when using the triangular coherence function, the detection range is set within a linear slope of the triangle so that the stress location is directly converted into the value of the coherence degree.     

The evolutions of the spectrum and spatial coherence of laser radiation in resonators with hard apertures and phase modulation

The evolutions of the spectrum and spatial-coherence of light in optical resonators are investigated theoretically in detail on the basis of coherence theory in the space-frequency domain. The initial light in the resonator is assumed to be polychromatic and spatially incoherent with a certain spectral width. By considering the effects of the edge diffraction and phase modulation, the evolutions of the spectrum and coherence are clearly demonstrated for different types of resonator. The results show that the spectral evolution is affected not only by the g-factor of the resonator (the type of resonator), but also by the edge diffraction and phase modulation. We introduce a new parameter, called the global degree of spatial coherence, to characterize the spatial coherence on each mirror. The spatial-coherence evolution is also affected by g-factor of the resonator, edge diffraction, and phase modulation. The physical mechanism of these phenomena is explained and discussed.     

基于激光冷却技术的中性锶原子特性研究

为了研究碱土金属类的中性锶原子在多普勒冷却激光场中的冷却特性,从Heisenberg方程出发,采用激光冷却理论分析得到锶原子在能级跃迁（5s2）1S₀~（5s5p）1P₁ 1维驻波激光光场和3维磁光阱中冷却效果与激光强度、失谐量等冷却激光场参量的关系。结果表明,当锶原子处在1维驻波激光光场中且在弱激光光场、频率小失谐条件下,锶原子所受耗散力与这两个参量呈线性关系,但当两个参量增长至一定程度时耗散力呈现饱和现象;当锶原子在3维磁光阱中且当阱中激光光场的频率失谐为-16MHz时,碱土金属锶原子有最低冷却温度,约为0.76mK。对多普勒冷却光场中性锶原子特性的分析为其它碱土金属类原子的冷却研究提供了一定的理论指导。     

Galvanic vestibular stimulation elicits consistent head-neck motion in seated subjects

Humans actively stabilize the head-neck system based on vestibular, proprioceptive and visual information. Galvanic vestibular stimulation (GVS) has been used previously to demonstrate the role of vestibular feedback in standing balance. This study explores the effect of GVS on head-neck kinematics and evaluates the approach to investigate the vestibular contribution to head-neck stabilization. GVS was applied to 11 seated subjects using seven different stimuli (single sinusoids and multisines) at amplitudes of 0.5-2 mA and frequencies of 0.4-5.2 Hz using a bilateral bipolar configuration while 3-D head and torso kinematics were recorded using motion capture. System identification techniques were used evaluating coherence and frequency response functions (FRFs). GVS resulted in significant coherence in roll, yaw and lateral translation, consistent with effects of GVS while standing as reported in the literature. The gain of the FRFs varied with frequency and no modulation was observed across the stimulus amplitudes, indicating a linear system response for the stimulations considered. Compared to single sine stimulation, equivalent FRFs were observed during unpredictable multisine stimulation, suggesting the responses during both stimuli to be of a reflexive nature. These results demonstrate the potential of GVS to investigate the vestibular contribution to head-neck stabilization.     

Simulation of ocean waves imaging by an along-track interferometricsynthetic aperture radar

A two-dimensional (2D) model for describing the imaging of ocean waves by an along-track interferometric synthetic aperture radar (AT-INSAR) is derived. It includes the modulation of the normalized radar cross section by the long waves, velocity bunching, and azimuthal image smear due to orbital acceleration associated with long waves and due to the orbital velocity spread within the AT-INSAR resolution cell (parameterized by the scene coherence time). By applying the Monte-Carlo method, AT-INSAR amplitude and phase image spectra are calculated for different sea states and radar configurations. The Monte-Carlo simulations show that velocity bunching affects the AT-INSAR imaging mechanism of ocean waves, and that a unimodal ocean wave spectrum may be mapped into a bimodal AT-INSAR phase image spectrum due to an interference between the velocity term and the velocity bunching term in the AT-INSAR imaging model. It is shown that the AT-INSAR imaging mechanism of ocean waves depends on the ratio of the scene coherence time and the time separation between the observations by the two antennas. If this ratio is larger than one, the AT-INSAR phase image spectra are distorted. Furthermore, the simulations show that the AT-INSAR phase image spectrum is quite insensitive to the ocean wave-radar modulation transfer function. Comparing AT-INSAR with conventional SAR imaging of ocean waves, the authors find that the azimuthal cut-off in AT-INSAR phase image spectra is shifted toward higher wavenumbers than in conventional SAR image spectra. This implies that AT-INSAR can resolve shorter azimuthal wavenumbers than conventional SAR. Thus the authors conclude that AT-INSAR phase images are better suited for measuring ocean waves spectra than conventional SAR images     

激光显示中散斑减弱的研究

简述了散斑的形成机理,具体分析了在近场条件下通过降低激光的时间或空间相干性来抑制散斑的方法,以及仅通过降低激光的相干性来减弱激光显示中散斑的缺陷。提出一种全新在远场条件下减弱散斑的超声光栅法,且详细说明了超声波减弱散斑的工作原理。当合成的激光束通过因超声波在液体媒介中的传播而形成的"位相光栅"时,激光发生衍射,通过一系列透镜将所有衍射光完全会聚到投影屏幕上,投影移动的干涉条纹在屏幕上产生"沸腾"的散斑图样,考虑到人眼的视觉暂留特性。散斑在人眼中得到均匀化。以绿光为例,说明了激光束通过"位相光栅"时,经过CCD相机和图像处理系统,显示屏幕上散斑对比度和光强的变化,显示了超声光栅法有效地抑制了激光显示中的散斑现象。     

弹性波在受拉钢绞线中传播的耦合与衰减

基于超声波的无损检测方法在钢绞线健康监测检中得到了越来越多的关注。目前大多数研究将钢绞线视为整体来研究弹性波在其中的传播特性,而很少研究弹性波在钢丝绞线间的传递及相互耦合。该文从单根钢丝的角度出发,分别通过仿真和实验的方法,在外围单根钢丝线中激励弹性波,测量其余钢丝线中的响应,分析弹性波在钢丝线间的传递关系。仿真和实验结果表明,在受拉钢绞线中,弹性波从激励钢丝线到其余钢丝线的传递率相同,与几何位置无关。随后改变信号接收位置,得到了弹性波随传播距离呈指数衰减的规律。     

高斯和超高斯型随机相位调制的光腔模式

本文利用空间－频率域相干模式理论对内置高斯或超高斯类型的随机相位调制的腔内模式进行了数值分析。结果表明：在这种随机相位片调制下,通过控制参数,可以在一腔镜上得到部分相干的类超高斯分布的光束,且类超高斯阶次可由相位参数控制;本文还引入新的参量－平整度来描述光束的整体强度分布的特征。     

Ultrasonic interferometry: study of particle sedimentation inliquid

An ultrasonic interferometry method was designed to study sedimentation of particles in liquid. The method, based on A mode echography, measures the amplitude of ultrasonic waves reflected (echo E1) by a fixed interface I1 called "solid plate-sediment" interface formed when particles are sedimenting on a solid plate. The amplitude of the echo depends both on mechanical properties of the three media (solid plate, sediment and suspension) on the thickness of the sediment and on the presence of a second mobile interface I2 called "sediment-suspension" interface. In the first phase of sedimentation when the second interface is very close to the first, two reflected waves interfere. Then, in the second phase of sedimentation when the sediment is thick enough, the amplitude of the echo E1 depends only on the sediment and solid plate properties. The first phase will give information on the sedimentation rate of particles (SR). We have compared SR of particles determined by this method with SR measured in a cylindrical tube of the same geometry as the ultrasonic measurement cell and with theoretical values of the sedimentation rate given by theoretical models.