利用细棒润湿效应弯曲液面边界反射的研究

发现了细棒润湿效应时弯曲液面上边界反射光场的圆形暗场扩张效应.当平行激光束垂直入射到由细棒润湿效应引起的弯曲液面上时,边界反射产生特殊的反射图样,图样的中心为圆形暗场,周围有清晰的衍射条纹,并且暗场的半径随入射光束半径的缩小而变大.理论上分析了反射图样暗场的半径与边界入射光束半径的解析关系,实验室上计算了弯曲液面的斜率,进而得出弯曲液面上升的最大高度和接触角.建立了一种利用弯曲液面边界反射的暗场扩张效应来实时测量液面特性的新方法.     

分划板失调对猫眼光学系统反射特性的影响

为了研究猫眼光学系统中分划板失调对入射光束的反射特性影响,考虑光学元件的等效光阑作用,将失调光阑孔径函数展开为有限项复高斯函数之和,利用失调光学系统的广义衍射公式,推导出入射光束经含分划板失调猫眼光学系统的反射光束场分布的近似解析式,得到反射光束场分布与入射光束光学参量、分划板孔径尺寸和分划板失调量之间的关系,对特定猫眼光学系统定量分析了分划板失调对反射光束场分布的影响。结果表明,分划板失调对反射光束场分布产生影响,特别是对远场光场分布影响显著。     

高斯光束斜入射非平行薄膜滤光片的反射光强分布

基于多光束干涉原理,推导了非平行角度调谐薄膜滤光片在斜入射时的高斯光束反射光强表达式。在此基础上研究了高斯光束的入射角以及非平行滤光片两端面间所存在楔角对反射光强分布的影响。计算和实验结果都表明,滤光片的反射光强分布不仅与入射角有关,而且非平行滤光片两端面间楔角的大小和正负特性还会在一定程度上影响斜入射时滤光片的光场分布、反射率和隔离度。要保证滤光片在斜入射时反射率和隔离度的稳定,既可以在切片时提高滤光片的平行度,也可以通过在斜入射时保证楔角为负来实现。     

平行金属线阵列地面附近的早期HEMP环境

铺设金属网的地面作为一种复杂的地表,区别于均匀半空间均匀地面,金属网必然会影响地表附近上方的电磁环境,因此,对其电磁环境的准确描述和分析十分必要。为此,以地面铺设平行金属阵列为典型情形,提出了一种计算平行金属阵列地面附近上方高空核爆电磁脉冲环境的解析方案,并且分析了地面铺设平行金属阵列结构之后对早期高空核爆电磁脉冲环境的影响。结果表明：当地面铺设平行金属线阵列后,相比于均匀半空间地面而言,不同高度下的水平极化场,反射场与入射场相互抵消的现象更加明显,使得总水平极化场衰减更为严重;而对于不同高度下的垂直极化场,其反射场和入射场的叠加现象也更加明显,使得地面附近上方的垂直场强幅值大于入射波场强幅值的效应加强。     

飞机燃油管道中的润湿阻力及其光学测量

文中建立一种激光测量燃油管道润湿阻力的方法及实验装置。得到了小流管条件下润湿阻力大小的解析表达式,即液体表面斜率与反射亮场及入射光通光半径之间的解析关系。根据弯曲液体表面光反射原理及光电自动检测原理,建立了润湿阻力的激光测量实验装置。依据激光反射图样光斑大小可以测出液面的斜率和液面与管壁的接触角。再根据润湿阻力的解析式,得到了润湿阻力大小。实验上,观察到特殊的弯曲液体表面激光反射图样,该图样为圆形光斑,具有明显的干涉圆环。圆形光斑的大小不仅与入射光通光半径有关,而且与表面的弯曲度有关。理论上润湿阻力的大小与液体的表面张力成正比,与接触角的余弦值成正比。本装置具有无损和自动化特点。     

有限宽度平面光波在非线性光学界面上的反射特性

利用计算机数值模拟的方法,取一系列不同的入射光强研究了由线性光学介质与非线性光学介质所构成的非线性光学界面的反射特性。将这结果与二维高斯光束的情况进行比较,发现有限宽度平面波在非线性光学界面上的反射特性是有明显差别的。在n_2≤0.01的非线性界面上,有限宽度平面波与高斯光束的反射光强分布明显地不同,前者沿界面已有相当一部     

矩形光阑限制下高斯光束的衍射特性分析

为了研究矩形光阑边长与透镜像方焦面处光束光斑尺寸以及光斑内所包含功率的关系,根据高斯光束经矩形光阑和透镜变换后在透镜像方焦面的衍射场分布表达式,采用MATLAB进行数值计算的方法,进行了理论分析。结果表明,当光阑对光束的衍射影响明显时,光束衍射场的中央亮条纹的宽度随着光阑边长的增大而减小;当光阑对光束的衍射影响极小时,中央亮条纹的宽度随着光阑边长的增加而阶跃变化,中央亮条纹强度的半最大值宽度随着光阑边长的增大而减小;当光阑对光束衍射影响极小时,中央亮条纹半最大值宽度趋近于一定值。给出的中央亮条纹强度半最大值宽度与矩形光阑边长关系的拟合表达式,可为激光应用装置的设计提供理论支持。     

径向偏振相干光束阵列的深聚焦

调整相干光束阵列中单元光束的线偏振方向可以得到近似的径向偏振光,但其特性与理想的径向偏振光存在差异。基于Richards-Wolf矢量衍射积分理论,利用数值方法对径向偏振相干光束阵列的深聚焦场进行了分析。研究了实际应用中较为关注的主要参数,即焦面上轴向偏振场及总场主瓣宽度、轴向偏振场的纯净度及产生效率。结果表明,与理想径向偏振光不同,径向偏振相干光束阵列的深聚焦场在焦面上会出现角向偏振分量。采用单环排布并使光束紧贴透镜瞳面边缘,可以产生质量更好的轴向偏振场。对于单环排布阵列,增多光束数目对轴向偏振场及总场主瓣宽度、轴向偏振场的纯度影响不大,但可以提高轴向偏振场的生成效率。     

CO2激光气化切割非金属材料的机制分析

研究了CO2激光气化切割高吸收率非金属材料的机制。基于实验拍摄的前沿形状和切缝形状，经过理论分析建立了激光气化切割非金属材料的三维能量耦合模型，分析了实际弯曲切割前沿和两壁面对激光的反射和能量吸收过程。前沿和壁面的能量吸收主要决定于入射光束的前三次入射(即两次反射)，前沿本身的多次反射增强了前沿底部的功率密度，而壁面的多次反射增强了前沿中下部位的功率密度。正是由于多次反射的存在，使得整个前沿都有功率密度分布。两切口壁面对入射激光有波导作用，入射激光在左右两壁面之间相互反射，朝着切口深部传输，即所谓的“壁面聚焦效应”(Wall focusing effect)。     

光热失调技术的实验研究

光热失调技术是利用光学薄膜反射或透射光谱的温度效应研究薄膜吸收的一种新方法,是光热技术的一种.以BK7玻璃为衬底的高反射膜为样品,以连续激光为加热光源,实验研究了该方法反射和透射探测方式,以及加热光束入射角度对光热信号的影响,得出反射和透射光热信号相位相反,加热光束入射角对光热信号的影响较小,进一步验证了光热失调技术测...     

激光引力波望远镜镜面杂散光测试方法

激光引力波望远镜的杂散光来源主要是细光束入射到镜面产生的反射杂散光。1 W的激光入射产生的杂散光需抑制到10-10 W以下,否则将严重影响主要参数光程差的测量精度。针对该应用背景,考虑了在细光束入射到镜面条件下由杂散光测试数据重构表征镜面反射特性的双向反射分布函数（BRDF）参数的可行性。传统方法测量BRDF需要4个转角,系统复杂不便于实时应用。为此基于光学元件各向同性和镜面杂散光模型的对称性,综合考虑了平面镜、曲面镜以及光束衍射效应、测量误差等因素,提出了一种仅利用子午面内一维测量若干个点的散射数据即可重构得到BRDF参数的方法,并用数值方法对其可行性和测量精度进行了验证。     

Features of propagation of surface acoustic waves in two-dimensional phononic crystals on the surface of a lithium niobate crystal

Two-dimensional phononic crystals are fabricated on the surface of a lithium niobate crystal. A numerical method is developed for calculating the frequency dependences of the transmission and reflection coefficients of a surface acoustic wave for a rectangular region with two-dimensional periodic structure on the surface of an elastic body. Measurements of the frequency dependences of the reflection and transmission coefficients are performed for propagation in the part of the lithium niobate crystal surface on which two-dimensional phononic crystals were fabricated. Forbidden zones are found in the transmission spectra of the waves transmitted through phononic crystals. It is shown that, if the width of the incident wave beam is less than the width of the region with the two-dimensional periodic structure (the two-dimensional phononic crystal), then a resonant increase in the transmission coefficient arises near the center of the rejection band.     

Diffraction Properties of Blazed Gratings Illuminated with Broad-bandwidth and Divergent Beam

Far-field intensity and diffraction efficiency of the blazed reflection gratings illuminated with broad-bandwidth and divergent beam are investigated. When the spectral width and divergence of the incident beam with a constant energy increase, the maximum intensity decreases, and the half width at e^-2 of the maximum intensity becomes wider. Diffraction efficiency has no deterioration for the blazed grating with a proper groove shape even when the incident light contains a broad range of wavelengths and comes from a wide range of angles.     

Reflective spectrum broadened by nano-particle-network in chiral liquid crystals

Based on the analytical expression of the electromagnetic field solution of a helical symmetric dielectric material, the relationship between spectral reflectivity and birefringence of a chiral liquid crystal and the blue shift of the Bragg reflection in the condition of oblique incidence are presented in this paper. The theoretical results indicated that: 1) If birefringence (An)of the liquid crystal is greater than 0.2 and the thickness of the liquid crystal layer reaches 3μm, the liquid crystal layer will reflect more than 90% of the incident light; 2)To reflect the whole visible spectrum by Bragg reflection,An of the liquid crystals in plane alignment state should exceed 0.6; 3) When the incident beam inclines to 60°from the normal direction, the blue shift of the reflective spectrum will reach to 100 nm. On the other hand, since the An of the commercial chiral liquid crystals is not larger than 0.2, to get the entire visible reflective spectrum, it needs to introduce a polymer network into the liquid crystals and make a sagging structure on the surface of substrates. The contribution of the network is to establish random anchorage that makes the pitch varied, hence broadening the Bragg reflection spectra.The random distribution of the sagging structure on the surface substrate is used to induce random screw axes of the chiral liquid crystal, which not only causes a blue shift of Bragg reflection but also further stretches the reflection spectra. Experiments demonstrated that the Bragg reflection spectrum could be broadened from by introducing both polymer network and sagging structure on the substrate surface cell.     

激光在测定液体表面张力系数及折射率中的应用

实验发现 :激光束照射在振动的液面上 ,表面波对入射光可产生衍射 ;用扩束后的激光束入射在插入细针的液面区 ,其反射光场中心分布近似为一暗椭圆形。以上两种实验现象机理 ,可用于液体表面张力系数的测定。激光经小孔透射样品池中的液体介质 ,在液体上表面发生遮光效应 ,根据其机理 ,建立了一种测量液体折射率的新方法     

各向异性粗糙海面对掠入射激光的散射特性研究

针对目前粗糙海面的激光散射场模型并不适用于激光束掠入射的情况以及忽略风速的影响,基于Cox-Munk模型及基尔霍夫近似（KA）模拟各向异性粗糙海面,建立海面对掠入射激光束的方向反射率分布模型,仿真分析了方向反射率随风速、风向、入射角、入射方位角、反射角、反射方位角的变化规律,并通过水池实验进行了验证。结果表明:粗糙海面对激光束的散射能量主要分布在以被照射海面为顶点的圆锥形角空域,此空域角方向位于镜面反射方向附近,且随着风速的增加,空域角逐渐变大,对于掠入射的激光束,由于海浪的遮蔽效应,空域角方向会偏离镜面方向。该模型可以为激光半主动制导导弹对海上小目标射击研究以及利用激光束照射粗糙海面布设激光诱饵研究提供一定理论依据。     

Video camera system using liquid-crystal polarizing filter toreduce reflected light

We have been developed a video camera system using an electrically-controllable liquid crystal polarizing filter for television program production, which can quickly reduce undesirable reflected light from a window pane or watery surface, by automatically judging the polarization state of incident light from the change in video signal intensity. More than 80% of linearly-polarized incident light is removable by this method for all incident polarization angles. The time required for detecting and reducing reflected light is approximately 0.3s in our system. The drastic reduction of polarized light reflected from glass and watery surfaces was demonstrated, and object images obscured by bright reflected light were clearly captured in an instant     

An analysis of the photoinduced current from a finely focused light beam in planar p-n junctions and Schottky-barrier diodes

We present analytic expressions for the photocurrent generated by a highly convergent light beam from a microscope objective lens incident on both planar p-n junctions and Schottky-barrier diodes. The variation of the current as a function of surface recombination velocity, depletion region width, diffusion length, and objective lens numerical aperture are all discussed. We also consider the application of the technique as a method of measuring minority-carrier diffusion lengths, which is independent of variations in surface reflectivity.     

Curved Waveguide Array Diode Lasers for High-Brightness Applications

We have developed a novel structure for achieving high-brightness output from a semiconductor laser array using coherent spatial beam combination. The structure consists of an array of curved ridge waveguides with in-phase, coherent output. Interference of the multiple outputs leads to a narrow, bright, on-axis, far-field beam shape. Experimental results demonstrate a diffraction limited output beam width, ideal for high-brightness applications.