非对称光束干涉制备二维微纳光子结构研究

研究了基于不同偏振组合的非对称4束和5束光干涉制备二维微纳光子结构.通过改变光束的参数组合获得了枝节状、波形状等结构.在非对称光束干涉中,光束的构型和偏振改变了波矢差分布,从而改变晶格形貌和对比度.利用CHP-C感光胶开展了全息光刻实验制备,获得了与模拟一致的光子结构.该研究为制备新颖光子结构提供了有效途径,此类光子结构还可以为制备不同类型的金属点阵结构提供模板,对新型光子器件的制备和应用研究具有一定的促进作用.     

Laser diode beam shaping by optical interference

We recently proposed a novel beam shaping technique that employs Lloyd’s mirror interference. In this study, we apply this technique to three commercial laser diodes: laser diodes used for optical pumping of solid-state lasers, for laser beam printers, and for laser displays. The elliptical output beams from these laser diodes could be transformed into nearly circular beams by inserting a mirror-polished GaAs substrate below the active layer of each laser diode and adjusting its height. The experimentally observed far-field patterns were predicted fairly well by numerical calculations based on Huygens’ integral. We confirmed that our beam shaping technique is applicable to laser diodes with various wavelengths and vertical beam divergence angles. We also describe the monolithic configuration of the beam shaping system, which can be fabricated by dry etching.     

激光辐照下薄膜镜面波纹损伤机理研究

 用透镜将脉冲激光束聚焦在铝膜镜面上，在部分样品的激光损伤边缘区，出现波纹状损伤形貌。大多数情况下，有多套波纹同时存在，在镜面形成花纹，或者其中有一两套波纹占优势。提出了脉冲激光辐照下光学元件损伤区边缘产生波纹的一种光干涉模型：认为样品表面本身存在微米级杂质颗粒或者表面缺陷点在激光辐照下首先产生鼓包变形，鼓包或杂质颗粒将激光反射（散射）在未发生变形的区域，与直接辐照在该区域的激光束产生干涉，使得变形区周围的光强呈周期性分布，当变形区进一步损伤后，则在损伤区周围留下了波纹状图案。模拟实验验证了这种设想。     

激光捕获技术及其发展

激光捕获技术是利用光辐射力来捕捉、移动和操纵微粒的先进技术。光镊即单光束梯度力光阱是通过在高度会聚的激光束束腰附近所产生的极高的场强梯度来形成皮牛顿量级的力,可以三维地捕获和操纵微小粒子。阐述了激光捕获技术的模型和原理以及系统的基本结构;追踪了激光捕获技术的最新研究进展;介绍了非高斯型光阱、光纤光阱和全息光镊等几种特殊形式,并分析了每种形式的特点。展望了激光捕获技术的发展前景。     

非线性晶体产生的空心光束中大尺寸粒子囚禁与导引

提出了一种基于非线性ZnSe晶体产生的空心光束与光泳力的大尺寸粒子二维囚禁与一维导引、三维囚禁方案.理论上分析并计算了单个非线性ZnSe晶体产生的空心光束内粒子受到的横向与纵向光泳力,纵向光泳力的大小同粒子尺寸与光束尺寸比例的四次方成正比,与空心光束功率成正比,方向与光束传播方向一致.粒子尺寸与空心光束尺寸越接近时,横向光泳力的大小越大.结果表明该光泳力可以实现对大尺寸粒子的二维囚禁,同时可对粒子进行长距离(米量级)一维定向导引;理论上分析并计算了基于双非线性ZnSe晶体产生的局域空心光束内粒子所受横向与纵向光泳力情况,光泳力与系统参数的依赖关系与单个非线性晶体产生的空心光束中的粒子受力情况类似,不同的是该条件下纵向光泳力指向光束中心.结果表明该局域空心光束可以实现大尺寸粒子的三维有效囚禁.基于非线性ZnSe晶体产生的空心光束或者局域空心光束可以作为大尺寸粒子非接触式有效操控的工具,在现代光学以及生物医学中有潜在的应用.     

全光纤光反馈环形腔结构多路激光被动相干合成

提出了基于全光纤光反馈环形腔结构的多路光纤激光相干合成方案,实现了多路激光的被动相干合成。全光纤结构避免了传统孔径拼接输出结构的旁斑能量耗散问题,保证了合成光束的光束质量。开展了实验研究,实现了4路光纤激光的相干锁相输出,获得时域、空域特性均十分稳定的合成光束,合成效率为96.1%,取得较好的合成效果。     

基于衍射光学器件的多自由度测量仿真研究

提出了基于衍射光学器件的单光束多自由度测量的新方法。描述了该方法的基本原理,建立了相应的激光干涉系统的数学模型,设计了一种能够产生多自由度测量信息的衍射光学器件。分析了干涉场光强信号特征与目标各平动和转动量之间的关系,给出了仿真计算结果。该方法原理简单,测量效率高,并能提供较高的测量分辨率和测量精度。     

Direct measurement of three-body interactions amongst charged colloids

Three-body interactions amongst three charged colloidal particles are measured in a deionized aqueous solution. Two of the particles are confined to an optical line trap while the third one is approached by means of a focused laser beam. From the observed particle configurations we extract the three-body potential which is found to be attractive and roughly of the same magnitude and range as the pair interactions. In addition, numerical calculations are performed which show qualitative agreement with the experimental results.     

Observation of multi-path interference in broad-area semiconductor lasers with optical feedback

Multi-path interference effects induced by optical feedback in broad-area semiconductor lasers is experimentally studied. An external mirror and an internal laser cavity form a closed composite optical feedback loop. For a very small tilt of the external mirror for the exit facet along the stripe width of the active layer, the light emitted from the laser undergoes multi-path reflections in the composite cavity, and we therefore observe multi-path interference effects of the laser oscillations for a small mirror tilt. The laser output power always shows the fundamental mode of the single feedback loop together with an oscillation of a certain higher multi-path loop. The laser oscillation and the beam profile are strongly dependent on the tilt. We observed up to a nine-fold multi-path interference in the experiment.     

光学系统像差与光场干涉对激光参量测量精度的影响

研究了采用面阵CCD探测器测量光束参量的技术问题,研制了一套高精度激光参量测量系统,对其光学系统像差与光场干涉原因进行了理论分析,实验测量了连续抽运1064nm固体模式发生器产生的基模厄米高斯光束,分析对比了其输出光束带有干涉条纹时对测量精度的影响,对光学系统的设计提出了具体技术要求,为同类装置的研制提供了参考依据。     

Sensitivity enhancement in thermal lens laser spectrometry

A novel experimental configuration for thermal lens detection is described. The method makes use of optical filtering of the probe beam by means of a circular aperture. This considerably reduces noise associated with intensity fluctuations of the probe beam. The technique provides an enhancement of the signal-to-noise ratio by almost one order of magnitude as compared to other thermal lens laser spectrometers. A theoretical calculation of the signal enhancement associated with optical filtering of the probe beam is presented. Furthermore, experiments on methyl blue dissolved in ethylalcohol are described which verify the theoretical predictions.     

Spiral interferometry

We present a surprising modification of optical interferometry. A so-called spiral phase element in the beam path of a standard microscope results in an interferogram of phase samples, for which the interference fringes have the shape of spirals instead of closed contour lines as in traditional interferograms. This configuration overrides the basic problem of interferometry, i.e., that elevations and depressions cannot be distinguished. Therefore a complete sample profile can be reconstructed from a single exposure, promising, e.g., high-speed metrology with a single laser pulse. The method is easy to implement, it does not require a spatially separated reference beam, and it is optimally stable against environmental noise.     

Optical bottles: A quantitative analysis of optically confined nanoparticle ensembles in suspension

We present a novel method, an optical bottle, that uses a focused laser beam to trap and a second laser to analyze optically confined multiple nanoparticles. A theoretical framework based on the mechanical equilibrium of the optical radiation pressure produced by the focused laser beam and the osmotic pressure produced by the enriched particle concentration in the optical trap is developed for analyzing the ensemble behavior of the optically confined nanoparticles. Experiments were conducted for fluorescently labeled polystyrene nanospheres and unilamellar phospholipid vesicles to determine the optical trapping energy of individual particles as well as the osmotic compressibility of the colloids. The new method is not limited by the particle concentration and is relatively easy to implement.     

光纤相控阵稀疏排布优化算法对比

光纤相控阵在激光合束、激光雷达等领域具有应用前景.光纤阵列配置方式不同于微波相控阵,光纤天线间距大于波长时存在周期旁瓣问题,影响主瓣能量分布.本文从物理模型出发,建立了基于同心圆环形点阵集合的光学相控阵天线布阵理论模型,提出了利用解析延拓的傅里叶变换方法实现干涉场强度的快速合成理论,讨论了在离散采样时数值仿真需关注的采样带宽和采样数目问题,解决了快速实现多光束干涉场数值仿真的问题.对比研究了两种优化光学相控阵天线配置的优化算法:遗传算法和粒子群算法,分别实现了不同种群数量遗传算法和粒子群算法迭代优化,分析了二者在优化过程中的收敛速度和优化效果,得到了峰值旁瓣比PSR=0.270的配置阵列.所提出的方法有望用于实际的光学相控阵天线配置中,指导天线主瓣能量最大化的优化设计;研究模型对不可微分目标函数优化问题的研究有一定参考价值.     

Design and simulation of excitation laser system for <Emphasis Type="Italic">in-situ</Emphasis> Raman monitoring

A system for in-situ Raman monitoring of thin film growth during Microwave Plasma Assisted Chemical Vapour Deposition (μPACVD) process was developed. Dedicated Raman probe system was designed for precise focusing of an excitation laser beam into the growing film. The probes have to be placed outside the reaction chamber (working distance about 20 cm) in order to avoid interference of the process by work of measurement devices (non-invasive measurements). Analysis and calculation supported by simulations based on Monte-Carlo ray-tracing method and Beam Propagation Method showed that glancing-incidence optical configuration is of the Raman system is the most sufficient one. Range of the most effective incidence angles of the excitation beam was determined. Shape and size of laser spot at the sample was determined. Correction of spherical aberrations by use of doublets was proposed to ensure efficient focusing of the excitation beam into the investigated film.     

环镜对激光束变换的理论分析与实验

介绍一种新型的光学元件，它可把一束激光变换成一个两维的激光平面。本文用多光束干涉的原理解释了光平面形成的原理，同时对应用前景及实用情况也作了一些估计     

同材质颗粒不同填充密度的随机介质中光场的空间分布

用时域有限差分法研究了同一材质的颗粒在不同填充密度下的随机介质中光局域化问题. 依据随机介质激光的实验参数,模拟了颗粒填充密度不同的随机介质中光场的空间分布. 结果表明：当散射颗粒的散射平均自由程与波长相当时,随机介质中的光场分布呈现局域化的特征,而且随着颗粒填充密度增大,光场的局域化程度增强. 因此,在同样的抽运激励下,颗粒填充密度越大的随机增益介质越容易产生激光辐射. 数值模拟结果与实验定性符合. 关键词： 随机激光 时域有限差分法 颗粒填充密度 局域化     

Conversion of a high-order mode beam into a nearly Gaussian beam by use of a single interferometric element

We present a new, compact, and practical optical mode converter that efficiently transforms a high-order Hermite-Gaussian (HG) laser beam into a nearly Gaussian beam. The mode converter is based on coherently adding different transverse parts of the high-order mode beam by use of a single planar interferometric element. The method, configuration, and experimental results obtained with a pulsed Nd:YAG HG TEM10 laser beam are presented. The results reveal that the efficiency of conversion of a HG beam to a nearly Gaussian beam can be as high as 90%.     

Study on the possibilities of controlling the laser output beam properties by an intracavity deformable mirror

The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power transverse flow cw CO₂ laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters of the laser radiation.     

Quality factor of circular laser diode beam tailored by optical interference

The quality factor of a laser diode beam tailored by Lloyd’s mirror interference was investigated numerically and experimentally. The far and near-field patterns were analyzed by numerical calculations based on Huygens’ integral. An almost circular tailored beam was calculated to have a quality factor as low as 1.08. This beam-shaping technique was experimentally demonstrated using a commercial 640 nm laser diode and a mirror-polished GaAs substrate. The optical beam tailored by Lloyd’s mirror interference was nearly circular and its beam quality factor was measured to be 1.24. Although this measured beam quality factor is slightly higher than the numerically calculated one, it is acceptably low.