空间相位调制对光伏孤子传播的影响

利用空间相位调制技术控制高斯光束在光伏晶体中的传播.数值分析结果表明，适当地选择各调制参数，可以使光束以类孤子的形式传播，或使光束发生自偏转、分束、发散.还进一步就中心光强、半高全宽的大小对相位调制的影响作了定性的分析. 关键词： 空间光学孤子 空间相位调制 光开关 光偏转 光分束     

基于相控阵雷达模型的液晶光束偏转波控方法研究

针对闪耀光栅模型光束偏转角度数量分布有限的缺点,提出一种基于相控阵雷达模型的液晶光束偏转波控方法。该方法控制液晶电极间相位差,通过改变液晶电极间相位差控制出射光波束方向。使用傅里叶光学方法推导该模型最大偏转角度、光束偏转角度与电极间调制相位关系以及衍射效率和偏转角度的关系。实验证明该方法可实现任意分辨角的光波束扫描, 在0.15°光束扫描范围内实现优于20 μrad的连续光束偏转。     

空间相位调制对强非局域空间光孤子的影响

利用空间相位调制技术和数值分析的方法，讨论了高斯光束在强非局域非线性平板波导中的传输问题，发现只要介质的响应具有对称性,光束就会有相同的演化规律，可控的空间相位调制参数不仅能让光束自偏转还能实现分束，其全新特性在全光开关及分光器上有潜在的应用价值. 关键词： 强非局域空间光孤子 空间相位调制 光偏转 光开关     

导波光束偏转器的双稳态特性

利用LiNbO_3波导电光棱镜,验证了导波光束偏转器的双稳态特性.对此,利用调制特性曲线的高斯函数模型,作了必要的理论分析,与测量结果基本相符.     

高斯光束孤波演化过程中的自偏转

研究了无耗晶体的扩散效应对高斯光束在光伏光折变晶体中孤波演化特性的影响。结果表明，对于给定的与晶体参量匹配的高斯光束，晶体的扩散效应将造成高斯光束孤波演化的自偏转，而且其自偏转过程与同参量的屏蔽光伏明孤子的自偏转过程具有极其类似的特征。同时发现，高斯光束的波形即光束的横截面对其孤波演化的自偏转影响最大。比较了高斯光束孤波演化的自偏转与明孤波自偏转的理论曲线，结果表明，对于匹配的高斯光束，其自偏转程度与解析计算结果非常接近。     

星间激光通信光束微弧度跟瞄性能检测装置的设计原理

基于矢量折射定理,研究了透射光束通过双棱镜实现微弧度量级偏转的设计原理,解决了星间激光通信精跟瞄检测的难题。推导了正交双棱镜实现光束偏转的精确公式,提出以水平张角和垂直张角表达光束视场,并说明了单棱镜实现光束偏转的一般情况。根据设计指标和计算结果确定了棱镜的主要参量,进而对光束的偏转结果进行了数值模拟。最后的实验结果与模拟结果基本一致。结果表明:取棱镜棱角α为4°时,棱镜每旋转1′,透射光束变化约1μrad;分别控制双棱镜在其最小偏向角一侧小角度偏转,可以实现光束在水平方向和垂直方向500μrad范围内的精确扫描,装置的扫描精度可以达到0.2μrad。     

利用Mirage效应确定非均匀材料厚度方向的热扩散率分布

在热导率沿试样厚度按指数规律渐变的假设下，利用两种基本数学变换，求解了非均匀材料的热传导方程，得到了试样内及与其相邻媒质内的温度场解析解。再根据光热光偏转理论，确定了检测光束切向偏转分量的位相与调制频率之间的函数关系，如果利用熟知的由检测光束法向偏转分量测定试样热扩散率的技术，测定试样两表面的热扩散率，这样就可以由Mirage效应的两个偏转分量来测定试样热扩散率沿厚度方向的分布。本文给出有关的理论推导，同时也给出了人造金刚石试样内热扩散率分布的实验结果。     

高斯光束在外加空间调制电场的光折变晶体中的演化

研究了高斯光束在外加空间调制电场的光折变晶体中的演化,结果表明,在不同的外加调制电场作用下高斯光束的光场分布会随着外电场变化而被调制。重点研究了同相位和反相位以及相位差为π/2的高斯光束在外加空间调制电场的光折变晶体中的相互作用,在外加空间分布线性增加电场作用下出现了许多新的实用特性,通过调整外加电场分布,可以让两同相位相干光靠得更近而不发生融合,也可以让两靠得很近的反相位光束可控偏转,还可以控制相位差为π/2的两相干光束进行能量转移。这种连续变化的电场可以用阶梯分布的电场替代,为工程实现提供了可能。     

匹配高斯光束在耗散晶体中的孤波演化及偏转特性

研究了匹配的高斯光束在加外电场的耗散型光伏光折变晶体中的动态演化及其偏转特性.结果表明，对于给定的耗散系统，若该系统能支持某一特定的耗散全息屏蔽光伏明孤子，也可能找到与之相匹配的高斯光束，则该匹配的高斯光束能在此给定的耗散系统中演化成稳定的屏蔽光伏空间孤子.同时，考察了扩散效应对此匹配的高斯光束的影响，结果显示，扩散效应将造成此匹配的高斯光束孤波在演化过程中产生偏转现象，而且其偏转过程与之相对应的明孤子的偏转过程具有极其类似的特征.通过比较研究匹配的高斯光束与耗散全息屏蔽光伏明孤子的偏转特征曲线，我们发现，对于匹配的高斯光束，其空间偏转的数值计算结果与明孤子偏转的解析计算结果非常接近.总之，在耗散系统中，匹配的高斯孤波的动态演化特性(包括偏转过程)与耗散全息屏蔽光伏明孤波的演化特性是相符合的.因此，人们往往可直接用匹配的基模高斯光束代替耗散全息屏蔽光伏明孤波，为理论分析和实验研究提供了便利.     

基于空间光调制器的光束大角度扫描技术研究

为实现一束激光在90°锥形范围内的扫描，利用液晶空间光调制器在光束偏转控制时精度高、无机械惯性等优点，研究并建立了基于液晶空间光调制器的光束偏转和角放大光路系统。提出了空间光调制器的可编程相位调制算法和角放大光路结构，推导了空间光调制器光束偏转角度与相位灰度驱动图的关系，设计了角度放大倍率高于22倍的角放大光路系统。在此基础上，建立了光束扫描控制实验系统，对该装置角度出射范围进行了测量，将实际的角放大倍率与设计值进行对比。实验结果表明:研制系统的出射视场角可达91.22°，并可通过畸变校正实现出射视场角范围内的规则形状扫描。该研究在光束敏捷控制、无线激光通信、目标搜索与追踪等领域具有重要的研究价值和应用前景。     

Thermal buckling and natural vibration of the beam with an axial stick–slip–stop boundary

As a first attempt to study the dynamics of a heated structure with complicated boundaries, this paper deals with the thermal buckling and the natural vibration of a simply supported slender beam, which is subject to a uniformly distributed heating and has a frictional sliding end within a clearance. This sliding end is initially at a stick status under the friction force, but may be slightly slipping due to the thermal expansion of the beam until the sliding end contacts a stop, i.e., the bound of the clearance. The material properties of the beam are temperature-independent for low temperature, but temperature-dependent for high temperature. For each case, the analytic solutions for the critical buckling temperature and the natural frequencies of the heated beam are derived first. Then, discussions are made to reveal the effects of beam parameters, such as the ratio of beam length to beam thickness, the ratio of clearance to beam length and the temperature-dependent material properties, on the critical buckling temperature and the fundamental natural frequency of the heated beam. The study shows that both friction force and clearance have significant influences on the critical buckling temperature and the fundamental natural frequency of the beam. When the friction force is not very large, the clearance can greatly increase the critical buckling temperature. These conclusions enable one to properly design the stick–slip–stop boundary so as to improve the mechanical performance of the beam in thermal environments.     

Change of zonal flow spectra in the JIPP T-IIU tokamak plasmas

When Ohmically heated low-density plasmas are additionally heated by higher-harmonics ion-cyclotron-range-of frequency heating, heated by neutral beam injection, or strongly gas puffed, the intensity of zonal flows in the geodesic acoustic mode frequency range in the tokamak core plasma decreases sharply and that of low-frequency zonal flow grows drastically. This is accompanied by a damping of the drift wave propagating in the electron diamagnetic drift direction, turbulence by trapped electron mode (TEM), and the increase of the mode propagating to ion diamagnetic drift direction (ITG). In the half-radius region, TEM and high-frequency zonal flows remain intense in both OH and heated phases. ITG and low-frequency zonal flows grow in heated plasmas, suggesting a strong coupling between ITG and low-frequency zonal flow.     

Study of thermo-optical distortions in a plate active element with zigzag beam path

Phase distortions introduced into the laser beam propagating in a plate under diode pumping of the active element (AE) and for intentionally caused temperature gradients in the AE are studied. The temperature distribution along the optical axis of the active element is measured during its end diode pumping. Phase distortions of the test beam propagating through the nonuniformly heated active element are studied. Interference patterns are obtained and optical distortions of the test beam are measured at various temperature gradients in the crystal.     

非均匀激光辐照下硅镜热变形对光束传输特性的影响

 使用有限元法计算了硅镜在DF化学激光器非稳腔输出的中空非均匀激光辐照下镜面温升和反射面面形随时间变化的特性,使用65阶Zernike多项式对镜面面形进行了曲面拟合,使用光线追迹的方法计算了平行光束经不同数量硅镜反射后的光束波前分布PV值、Strehl比和Zernike像差系数随时间变化的特性。计算结果表明：在典型的DF激光器输出的中空方形光束辐照下,硅反射镜的热变形将使反射光束产生波前畸变,波前畸变中,y方向像散项占据主要地位,其次是离焦项;随着激光系统中反射镜面数量的增加,高阶像差系数将逐渐增大,且波前PV值与反射次数成线性关系。     

Space-selective growth of frequency-conversion crystals in glasses with ultrashort infrared laser pulses

We report on space-selective growth of a second-harmonic-generation beta-BaB(2)O(4) (BBO) crystal inside a BaO-Al(2)O(3)-B(2)O(3) glass sample at the focal point of an 800-nm femtosecond laser beam. A spherical heated region was formed during the focused laser irradiation through observation with an optical microscope. We moved the heated region by changing the position of the focal point of the laser beam relative to the glass sample. We grew BBO crystal continuously in the glass sample by adjusting the moving speed of the heated zone. Our results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.     

Features and Limiting Characteristics of the Heating of a Substance by a Laser-Accelerated Fast Electron Beam

The features of plasma formation in a substance heated by a laser-accelerated fast electron beam have been studied. These features are related to the ratio of the heating rate to the rate of energy loss because of radiation processes and electronic thermal conductivity, which are governed by the dependence of the energy of the heating beam particles on the beam intensity, which is characteristic of laser-driven electron acceleration. It has been shown that energy losses increase with the beam intensity and significantly limit the maximum temperature of the formed plasma. The possibility of generating an intense γ-radiation pulse of a nonnuclear origin because of the bremsstrahlung of laser-accelerated electrons has been discussed.

     

A Particle-in-Cell Simulation Study on Harmonic Waves Excited by Electron Beams in Unmagnetized Plasmas

The excitation of harmonic waves by an electron beam is studied with electrostatic simulations.The results suggest that the harmonic waves are excited during the linear stage of the simulation and are developed in the nonlinear stage.First,the Langmuir waves(LWs)are excited by the beam electrons.Then the coupling of the forward propagating LWs and beam modes will excite the second harmonic waves.The third harmonic waves will be produced if the lower velocity side of the beam still has a positive velocity gradient.The beam velocity decreases at the same time,which provides the energy for wave excitation.We find that it is difficult to excite the harmonic waves with the increase of the thermal velocity of the beam electrons.The beam electrons will be heated after waves are excited,and then the part of the forward propagating LWs will turn into electron acoustic waves under the condition with a large enough intensity of beam electrons.Moreover,the action of ions hardly affects the formation of harmonic waves.     

A CEMS apparatus for in situ studies of ion beam modified metals

An apparatus for CEMS studies of ion beam modified metals is described. The spectrometer can be coupled directly to the ion implanter. During ion bombardement the sample can be cooled to liquid nitrogen temperature or heated to about 500 K. CEMS measurements can be taken directly after ion beam modification between room temperature and liquid nitrogen temperature. As a first test of the performance of the apparatus CEMS spectra of boron-ion implanted iron at room temperature are presented.     

Glass modification by continuous-wave laser backside irradiation (CW-LBI)

We report on a permanent change in the physical properties inside glass that is rapidly heated and quenched with a continuous-wave (CW) laser beam. The absorption of the glass was enhanced by laser heating, and the heated spot moved by thermal radiation and conduction. To trigger the heating, an absorbent material was placed on the backside of a glass plate and irradiated through the glass. The laser beam can modify borosilicate glass with a high aspect ratio (∼100:1) at a rate of ∼130 mm/s. The modified zone consists of two concentric cylindrical zones and is crack-free.     

Measurement of the diameter of a laser beam

A new and simple technique for measuring the effective diameter of a laser beam used in material processing is described. The time for the temperature of a spot heated by the laser beam to rise to 90% of equilibrium is compared with that predicted theoretically for a Gaussian TEM₀₀ laser beam. A Gaussian beam diameter equivalent is thus deduced. This calculated diameter is of particular relevance to applications where the laser is used as a heat source.