Optical trapping of single fluorescent molecules at the detection spots of nanoprobes

We propose a scheme of optical trapping of fluorescent molecules, based on the strongly enhanced optical field due to surface plasmon resonances at laser illuminated metal tips or particles. A semiclassical approach is compared to a quantum-mechanical one. Attractive as well as repulsive forces are possible depending on the wavelength of the optical field. The trapping potential is shown to be strong enough to overcome the Brownian motion in water solution for common optical tweezer light inten-sities. Single molecule resonance Raman spectroscopy probes are particularly well suited for the trap-ping scheme. Finally we propose intracellular probing of the function of biomolecules as an application.     

Reflection Induced Voltage Change of Surface Emitting Laser for Optical Probing

We demonstrate a novel optical probing technique using the reflection-induced change in voltage of a GaAs vertical cavity surface emitting laser (VCSEL). We present the modeling and experiment of the VCSEL based probing. A two-dimensional image probing is successfully demonstrated.     

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.     

复杂激光系统中平板光学元件的调频-调幅效应的研究

为了抑制大口径光学元件中的受激Brillouin散射效应,并满足打靶过程中束匀滑的要求, 目前高能激光驱动器大都采用了正弦相位调制脉冲.然而,这类脉冲在复杂激光系统中传输时, 会出现明显的调频-调幅(FM-to-AM)效应.研究这种效应的来源,对提升激光系统的整体输出性能至关重要. 对复杂激光系统中一直被人们所忽视的平板光学元件带来的FM-to-AM效应进行了理论研究和数值模拟. 数值模拟结果表明,通过平板光学元件的次数越多调制深度越大,呈线性递增趋势,当通过次数为10次时, 调制深度高达22.2%;并且平板光学元件对各谱线的过滤也各不相同,当前端选用的中心波长为1054 nm时, 平板光学对各谱线的过滤作用非常小.提出通过改变中心波长来减小FM-to-AM效应, 这对于复杂激光系统的设计具有重要的指导意义.     

Study of ferroelectric switching by domain-wall induced light scattering

Measurements of 90°-scattering of weak laser light are used to investigate pulsed domain switching in ferroelectrics. The studies were performed on strontium-barium niobate (SBN) single crystals. A good agreement of the switching parameters estimated from the optical measurements with those obtained by means of conventional electrical methods proves the validity of the optical method for switching studies. Due to the limited scattering volume in all three spatial dimensions, the method facilitates local probing of the switching within the crystal bulk. In particular, local specialities of the domain density can be detected. Furthermore, the excellent time resolution inherent in optical probing techniques allows for a comprehensive study of the dynamics.     

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

C60高聚物复合固体材料的反饱和吸收过程研究

本文报导了新型材料C_(60)α-甲基苯乙烯/苯乙烯共聚物薄板的制作,并利用530nm,10ns激光研究此固体材料的激光透过特性.观测到反饱和吸收过程,即实现了光限制效应.     

利用光镊技术演示光的自旋角动量

阐述了光与物体相互作用时自旋角动量的传递与扭力矩原理.基于光镊光致旋转原理,利用能够悬浮单个粒子的光镊技术并采用具有双折射特性的CaCO3晶体粒子,设计了微粒在不同偏振光场中的旋转运动实验内容,研究光与双折射晶体粒子相互作用产生的光致旋转效应,观察和测量由自旋角动量引起粒子的扭转力矩的大小、方向以及旋转速度等力学效应.     

Multimodal nonlinear optical polarizing microscopy of long-range molecular order in liquid crystals

We demonstrate orientation-sensitive multimodal nonlinear optical polarizing microscopy capable of probing orientational, polar, and biaxial features of mesomorphic ordering in soft matter. This technique achieves simultaneous imaging in broadband coherent anti-Stokes Raman scattering, multiphoton excitation fluorescence, and multiharmonic generation polarizing microscopy modes and is based on the use of a single femtosecond laser and a photonic crystal fiber as sources of the probing light. We show the viability of this technique for mapping of three-dimensional patterns of molecular orientations and show that images obtained in different microscopy modes are consistent with each other.     

Method for probing the orbital angular momentum of optical vortices in electromagnetic waves from astronomical objects

We present an efficient method for probing the orbital angular momentum of optical vortices of arbitrary sizes. This method, based on a multipoint interferometer, has its most important application in measuring the orbital angular momentum of light from astronomical sources, opening the way to interesting new astrophysics. We demonstrate its viability by measuring the orbital angular momentum of Laguerre-Gaussian laser beams.     

用于Z-pinch诊断的266nm激光探针分幅阴影成像系统

采用Nd-YAG激光器的四倍频激光(266nm)设计了激光探针分幅阴影成像系统，该系统具有时间分辨率和收光效率高，测量范围大，可有效屏蔽可见光干扰的优点，在钨丝阵实验中成功获得晚期内爆等离子体的分布图像.对系统结构和性能参数做了介绍，对测量结果进行了讨论. 关键词： Z-pinch 激光探针 等离子体分布 分幅成像     

Ultra‐fast nano‐optics

Ultra‐fast nano‐optics is a comparatively young and rapidly growing field of research aiming at probing, manipulating and controlling ultrafast optical excitations on nanometer length scales. This ability to control light on nanometric length and femtosecond time scales opens up exciting possibilities for probing dynamic processes in nanostructures in real time and space. This article gives a brief introduction into the emerging research field of ultrafast nano‐optics and discusses recent progress made in it. A particular emphasis is laid on the recent experimental work performed in the authors' laboratories. We specifically discuss how ultrafast nano‐optical techniques can be used to probe and manipulate coherent optical excitations in individual and dipole‐coupled pairs of quantum dots, probe the dynamics of surface plasmon polariton excitations in metallic nanostructures, generate novel nanometer‐sized ultrafast light and electron sources and reveal the dipole interaction between excitons and surface plasmon polaritons in hybrid metal‐semiconductor nanostructures. Our results indicate that such hybrid nanostructures carry significant potential for realizing novel nano‐optical devices such as ultrafast nano‐optical switches as well as surface plasmon polariton amplifiers and lasers.     

Analysis of Center Wavelength Shift of VCSEL Light in AWG for WDM PON Applications

Center wavelength shift of vertical cavity surface emitting laser light in arrayed waveguide gratings is verified with mathematical and experimental analysis.It is induced by the linearly increasing trend of optical power of vertical cavity surface emitting laser by bias current increase.It is retrieved effectively to the original center wavelength by simple correction method of compensation.This was done for application of vertical cavity surface emitting laser as a light source in optical line terminal of wavelength division multiplexing-passive optical network.     

Laser polishing of diamond plates

Results are reported on laser polishing of 150–400-μm-thick free-standing diamond films with either a copper vapor laser (510 nm wavelength) or an ArF excimer laser (193 nm wavelength). Studies were focused on three particular goals. First, we aimed at a choice of optimum conditions for laser polishing of thick diamond films. It was shown that the laser polishing conditions and the resulting surface roughness were controlled by varying the angle of incidence of a scanning laser beam and by polishing time. Second, the laser ablation technique was applied to remove a defective layer from the “substrate” side of the diamond plates in order to reduce optical losses due to absorption in this layer. Third, the structure of the laser-graphitized diamond surface was studied using UV, visible, and IR optical spectroscopy techniques in the course of the “step-by-step” oxidative removal of the graphitic layer with increasing temperature of the oxidation in ambient air. Once the graphitic layer was removed, the optical transmission in the UV-visible-IR spectral range of the diamond films polished under optimum conditions was measured and compared with the optical transmission of the mechanically polished diamond films. It was shown that the optical quality (in the long-wave infrared region) of the laser-polished diamond plates was sufficient to reach the transmittance value very close to the theoretical limit. Received: 20 October 1998 / Accepted: 8 March 1999 / Published online: 5 May 1999     

Interference of speckle fields in the diffraction zone of a focused spatially modulated laser beam by a random phase screen

The processes of formation of average-intensity interference fringes upon diffraction by a random-phase object of a laser beam having interference fringes and focused on the surface of the object are considered. The dependences of the fringe contrast on the parameters of scattering inhomogeneities of the object and the parameters of the focused laser beam are established in analytical form for various diffraction regimes. Practical possibilities of a method of probing of scattering objects in problems of measuring the parameters of inhomogeneities and problems of interference-pattern formation in optical systems with scattering media are discussed.     

Monte Carlo方法模拟光在生物组织中传播的新进展

Monte Carlo方法已被广泛用于模拟复杂的随机介质如生物组织中光的辐射传输.在生物光子应用中,早期的Monte Carlo模拟模型忽略了光在组织中传输的波动性,而用中性粒子光子包来模拟其传播过程.然而,许多光学诊断技术是基于光在组织中的偏振效应和多重散射的相干性来揭示组织的生理和病理信息,这就要涉及光辐射的波动性.本文阐述了用Monte Carlo方法模拟光在生物组织中传播的最新进展.     

入射角和薄片表面特性对激光干涉测温的影响

以激光干涉为理论基础,采用具有不同表面光学特性的单晶硅片和K-8光学玻璃为样品,针对不同的测量条件,研究干涉条纹对比度变化对温度测量的影响.分析了薄片干涉条纹对比度与测量光束直径、入射角、样品表面粗糙度以及表面镀膜之间的相互关系,研究了薄片的横向温度梯度对干涉对比度的影响.实验结果表明,上述各因素对温度测量参量对比度产生的影响具有规律性,并在一定对比度阈值条件下,能够满足精确测温的条件要求.     

非线性光栅的自适应光限幅

首次采用液晶为自聚焦媒质,夹在内表面刻有光栅的两玻璃片间,以Ar离子激光514.5nm波长的激光束垂直入射到光栅上,实验验证了该光栅的自适应光限幅特征。     

Fast microstructuring of silica glasses surface by NIR laser radiation

The glass surface microstructuring technology using laser radiation with NIR wavelength (λ=1.064 μm) was revealed in this work. Glass plates were placed on the cellular graphite surface. Focused laser radiation passed through the glass plate and interacted with cellular graphite. The radiation heated the graphite surface and thus the high temperature influenced the back side of the glass plate. After consecutive laser scans, having certain periods and interruptions of laser radiation, the microstructures with depth ~0.5 μm were formed. Besides, in this work we suggested the method to calculate optical characteristics of formed elements. It was experimentally shown that these microstructures could be used to form phase diffraction gratings (PDGs) and random phase plates (RPPs). We experimentally demonstrated the possibility of these elements being used as RPPs which are suitable for multimode laser radiation homogenization and as PDGs which are suitable for laser simultaneous processing of metal films.     

光纤传输激光驱动飞片实验研究

构建了一种基于光纤传输高功率激光的飞片发射系统,并测试了飞片速度.飞片膜层为三明治结构:铝烧蚀层、氧化铝隔离层和铝飞片产生层.飞片膜层采用磁控溅射技术沉积在玻璃衬底上,总厚度为5.5 μm.激光辐照铝膜层产生高温高压等离子体,驱动剩余膜层产生高速飞片,速度达数km/s.同时,实验研究了光纤传能系统的输出激光空间分布特性和传输激光能量容量,它们决定了飞片的平面性和最大速度.光纤端面损伤是限制光纤传输激光能量容量的关键因素,光纤端面通过精密机械抛光和激光预处理可以获得理想的抗激光损伤能力.采用基于光纤阵列探针的时间序列测试技术获得了飞片的平均速度,并评估了飞片的平面性.采用搭建的基于光纤传输高功率激光的飞片发射系统获得了速度达1.7 km/s、直径接近1 mm的高速飞片. 关键词： 激光驱动飞片 激光辐照 光纤阵列探针 激光等离子体