Thin films by regular patterns of metal nanoparticles: Tailoring the optical properties by nanodesign

Ultrathin metal films consisting of regular two-dimensional arrays of 44–95 nm sized silver nanoparticles were fabricated by electron-beam lithography. By independent variation of particle shape and interparticle distance, respectively, the film's optical extinction maximum wavelength can be tuned in a range from 460 nm to 520 nm and the bandwidth between 50 and 100 nm. The results suggests the potential of lithographically designed nanoparticle films as thin layer material with tailorable optical properties for applications in microoptics and optoelectronics.     

Stable Fano-like plasmonic resonance: its impact on the reversal of far-and near-field optical binding force

Even for a 100 nm interparticle distance or a small change in particle shape,optical Fano-like plasmonic resonance mode usually vanishes completely.It would be remarkable if stable Fano-like resonance could somehow be achieved in distinctly shaped nanoparticles for more than 1μm interparticle distance,which corresponds to the far electromagnetic field region.If such far-field Fano-like plasmonic resonance can be achieved,controlling the reversal of the far-field binding force can be attained,like the currently reported reversals for near-field cases.In this work,we have proposed an optical set-up to achieve such a robust and stable Fano-like plasmonic resonance,and comparatively studied its remarkable impact on controlling the reversal of near-and far-field optical binding forces.In our proposed set-up,the distinctly shaped plasmonic tetramers are half immersed(i.e.air-benzene)in an inhomogeneous dielectric interface and illuminated by?circular?polarized light.We have demonstrated significant differences between near-and far-field optical binding forces along with the Lorentz force field,which partially depends on the object’s shape.A clear connection is shown between the far-field binding force and the resonant modes,along with a generic mechanism to achieve controllable Fano-like plasmonic resonance and the reversal of the optical binding force in both far-and near-field configurations.     

Localized vibrational modes in optically bound structures

We show, through analytical theory and rigorous numerical calculations, that optical binding can organize a collection of particles into extended, periodic one-dimensional lattices. These lattices, as well as other optically bound structures, are shown to exhibit spatially localized vibrational eigenmodes. The origin of localization here is distinct from the usual mechanisms such as disorder, defect, or nonlinearity but is a consequence of the long-ranged nature of optical binding. For an array of particles trapped by an interference pattern, the stable configuration is often dictated by the external light source, but we observed that interparticle optical binding forces can have a profound influence on the dynamics.     

菌紫质光致变色吸收特性的二能级理论研究

采用二能级模型(B态和M态)简化菌紫质(bR)光循环过程,建立了菌紫质光致变色吸收特性的数学方程,数值计算了bR膜对570nm单光束和对570nm与412nm双光束的吸收特性.计算表明,bR膜的光吸收特性与入射光波长、入射光强、摩尔消光系数、光密度和M态寿命有很大的关系.bR膜用于光存储时,读出光强和M态寿命是影响bR读出使用时间的两个重要因素.570nm与412nm双光束作用于bR膜时,可以实现以光控光操作,但由于570nm黄光的透过动态范围要比412nm紫光的透过动态范围大得多,因而在实际应用中应以黄光作为信息光,紫光作为控制光.基于bR膜对黄、紫光束的吸收特性,可以将其应用于亮背景滤除、反象器、图象相减、光寻址空间光调制器等光信息处理领域.     

基于神光Ⅱ的激光黑腔靶全孔径背反散射光信号

介绍了神光Ⅱ装置激光黑腔靶实验中全孔径背反系统的工作原理,分析了激光靶耦合背反系统对散射光的收集情况,发现打靶产生的散射光完全进入背反收光系统,同时,8路激光对穿打靶时全孔径背反系统中存在杂散背景光。采用场图感光纸结合滤光片的方式对杂散背景光成分进行了分析,结果表明,杂散光的成分为打靶激光倍频过程中剩余的部分二倍频和基频光。在北4路激光注入打靶时,用南4路全孔径背反系统的能量测量系统对南4路背反系统中的杂散光进行了监测,显示杂散光对背反系统SRS能量测量的影响约为15%。     

Multicomponent periodic nanoparticle superlattices

In this article, we review the state-of-the-art in the preparation and characterization of multicomponent self-assembled superlattices of colloidal nanoparticles with core sizes in the range of 2–20 nm and interparticle spacing less than 2 nm down to intimate contact stemming from sintering. Several aspects of the field are discussed, including: structural organization, the role of particle size distribution, key interparticle forces at play, and methods of investigation of the structures. Contrary to the extensively studied colloidal crystals composed of microscale particles, the nanoparticles possess unique size-dependent properties, such as electronic, optical, or magnetic, which when combined into periodic structures can potentially lead to new collective states stemming from precise positioning of the nanocolloids. As such, we examine a number of emerging applications of this new class of metamaterials. Finally, we speculate on the potential impact of these materials, the new directions, and the challenges for the researchers.     

Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification.The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol.With the saturated amplification,we can obtain high energy incoherent light pulses,whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy.Moreover,the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy.Selecting s-polarized fluorescence with a Glan-Taylor prism,the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed.The maximum output energy is 0.67 mJ for the optical parametric amplifier.By using an optical filter and compressor,the generated high energy incoherent light has great potential as the incoherent pump,signal or idler wave of a parametric down-conversion process,so that a wave with a high degree of coherence can be generated from an incoherent pump light.     

适用于色敏解调的光位移传感器宽带LED

为保证光位移传感器的工作性能,输入光源在500~800 nm波长范围内需具有较高的光谱能量,照明用LED波长在700 nm以上光谱能量陡降,限制了传感器的工作范围.针对照明用LED光谱能量不足的问题,研制出适用于色敏解调光位移传感器的宽带LED光源.首先利用单色仪对光位移传感器色敏元件WS7.56的性能进行了测试,依据色敏解调结果提出了光位移传感器正常工作所需的输入光源的光谱能量阈值.在照明用LED光谱特性基础上,配比掺杂氮氧化物红色荧光粉提升LED红光及近红外光光谱能量,得到了满足输入光源光谱能量阈值的宽带LED.最后,对该宽带LED光位移传感器进行了位移测量实验,实验结果较使用照明用LED光源有明显改善,位移解调线性度良好.本文研制的宽带LED光源体积小、效率高,是光位移传感器较为理想的宽带光源.     

一种新型的专用于光学相干层析系统的宽带光纤光源

报道了一种新型的专用于光学相干层析系统的输出光谱为准高斯型的宽带超荧光光纤光源.该光源采用掺饵光纤作为增益介质.其关键技术是在抽运源的输出端增加了光耦合器，并在光源输出端插入多级长周期光纤光栅对铒离子的自发光谱进行调制和整形；同时采用光控器和温控器来控制抽运源的输出以提高光源输出功率的稳定性.该光源的中心波长为1.57μm，输出光谱的3dB带宽大于75nm，输出功率为27mW.实验结果表明，该光源输出光谱的自相关函数的旁瓣峰被大大削弱，可以满足光学相干层析系统的应用. 关键词： 光学相干层析术 超荧光光纤光源 长周期光纤光栅 光耦合器     

Novel split-band erbium-doped fiber amplifier

In this paper we design a 120 nm bandwidth erbium-doped fiber amplifier using a seed light injection method for the first time. It is shown that when the wavelength of the seed light varies from 1520 to 1570 nm, the gain at 1610 nm reaches maximum near 1553 nm and increases as the seed light power. Based on the method, a novel split-band EDFA configuration is designed. The split-band architecture employs a 1550/1610 nm waveband multiplexer/demultiplexer and two independent sub-bands which pass in parallel through separate branches of the optical amplifier. The signals at independent sub-bands are combined and flattened before output, resulting in a broadband gain-flattened optical amplifier with 120 nm bandwidth.     

理论构造周期极化KTiOPO_4晶体制备852和1550nm双色纠缠光

利用KTiOPO4(KTP)材料非线性系数d33对应的二阶非线性0-类准相位匹配,理论上设计构造了一种周期极化KTiOPO4晶体(PPKTP),当晶体温度为20℃时,晶体准相位匹配格子的周期为10.70μm。波长为550nm的激光泵浦由该晶体组成的光学参量振荡器能产生含852nm信号光和1550nm的闲置光的双色纠缠,其中信号光对应Cs原子吸收线,闲置光1550nm对应光纤通讯波长。该纠缠光对量子信息网络和原子信息存储有非常重要的意义。     

Optical manipulation of plasmonic nanoparticles

We investigate numerically the optical forces exerted by an incident light beam on metal nanoparticles (MNP) sustaining the so-called localized surface plasmons (LSP). We first describe how the particle dispersion can be used to tune the respective contribution from extinction and gradient forces. By a suitable adjustment of the illumination conditions, single MNP can be selectively guided, sorted and trapped. The second part of our work investigates the interparticle forces existing within a MNP ensemble. Our results show that MNP located in a conventional optical trap can self-arrange under optical forces according to specific architectures. In particular, at very low distances, they tend to agglomerate into metal clusters leading to very high field concentration in the interstices. PACS 71.45.Gm; 71.36.+c; 87.80.Cc     

Near-field 3D mapping of spiral light structures formed by a polymer nanocylinder

It is demonstrated that polymer nanocylinders can form spiral light structures. Spiral distributions of light intensity are observed at distances of 230–1100 nm above the nanocylinder with a diameter of 700 nm and a height of 1100 nm. The optical spirals are measured using a scanning near-field optical microscope that performs 3D scanning over planes when the nanocylinder is illuminated from the bottom with linearly polarized CW He-Ne-laser radiation at a wavelength of 632.8 nm. It is shown that the topology of the optical spirals significantly depends on the incident polarization.     

Gummic acid stabilized γ-Fe2O3 aqueous suspensions for biomedical applications

Biomedical applications of magnetic nanoparticles depend critically on their preparation as aqueous colloidal suspensions, or ferrofluids, with long term stability under physiological conditions. Dispersion of the magnetic nanoparticles is generally achieved by the use of protein cages, polysaccharide, polypeptide and charged macromolecular coatings, which minimize interparticle magnetic interactions, particle agglomeration and precipitation. The synthesis and characterization of gummic-acid stabilized maghemite ferrofluids is reported. X-ray diffraction, transmission electron microscope and dynamic light scattering measurements give a γ-Fe₂O₃ magnetic core diameter of 8 nm and a nanocomposite particle hydrodynamic diameter of 50 nm. Mössbauer and magnetization measurements indicate the presence of isolated, sterically stabilized superparamagnetic nanoparticles resistant to aging, and thus, promising agents for the production of novel magneto-pharmaceuticals.     

Phase-coherent optical frequency division by 3 of 532-nm laser light with a continuous-wave optical parametric oscillator

Phase-locked 3:1 division of an optical frequency was achieved with a continuous-wave monolithic optical parametric oscillator (OPO) pumped by a 532-nm Nd:YAG laser, by use of 5% MgO-doped LiNbO(3) as a nonlinear optical crystal. The OPO generated signal light (798 nm) with 4-mW power and idler light (1596 nm) with 3-mW power for a pump power of 68 mW. Approximately 2microW of second harmonics (SH's) of the idler light was produced by external-cavity-enhanced SH generation by use of a periodically poled LiNbO(3) crystal. The beat signal between the signal light and the SH of the idler light was observed with a signal-to-noise ratio of 40 dB at a 10-kHz bandwidth and was successfully phase locked to a signal from a synthesizer through the electro-optic effect of the crystal.     

辐射变色膜片对质子剂量响应的实验标定

利用串列静电加速器产生的5~9 MeV的质子束对HD-810型辐射变色膜片（RCF）进行了标定。用分光光度计和普通的商用平板扫描仪对辐照后的RCF透过率进行了测量,得到了光学密度变化随RCF灵敏层吸收剂量的变化曲线。标定实验结果表明:在一定的吸收剂量范围内,RCF的光学密度变化与RCF灵敏层中吸收剂量成线性关系,并且与质子能量无关。测量光学密度所用光源的波长对线性范围的大小有较大影响,绿光(532 nm)比红光(670 nm)有更大的剂量探测范围。     

Writing 40 nm marks by using a beaked metallic plate near-field optical probe

We have developed a near-field optical probe that uses a triangular metallic plate with a three-dimensionally tapered apex as a light source for thermally assisted magnetic recording. Numerical analysis using a finite-element method shows that the size of the optical spot generated at the apex is 15 nm x 20 nm, and the efficiency (defined as the ratio between the power of the optical near field at the surface of the recording medium and that of the incident light) is 15% when the incident light is focused by a lens with a numerical aperture of 0.8. The metallic plate was fabricated on the surface of a quartz slider and used for writing marks on a phase change recording medium. The marks were observed with a scanning electron microscope, and we confirmed that marks with a diameter of 40 nm were successfully written on the medium.     

基于聚合物的橄榄球形光学微谐振器

利用苯二甲酸丙二醇酯(PTT)聚合物微米线从生物相容性聚合物材料聚乙烯吡咯烷酮(PVP)水溶液中提拉制备得到直径为10～300μm的橄榄球形光学微谐振器。将波长为532nm的绿光和波长为671nm的红光分别耦合到最大直径为94.7μm和68.3μm的橄榄球形微谐振器,观察了其谐振特性。利用1549～1552nm的连续光源对直径为94.7μm的橄榄球形微谐振器进行了光学性能测试,测量了其吸收光谱。观察到明显的回音壁模式吸收峰,测得其品质因子为1.05×105。     

In situ characterization of an optical cavity using atomic light shift

We report the precise characterization of the optical potential obtained by injecting a distributed-feedback erbium-doped fiber laser at 1560 nm to the transverse modes of a folded optical cavity. The optical potential was mapped in situ using cold rubidium atoms, whose potential energy was spectrally resolved thanks to the strong differential light shift induced by the 1560 nm laser on the two levels of the probe transition. The optical potential obtained in the cavity is suitable for trapping rubidium atoms and eventually to achieve all-optical Bose-Einstein condensation directly in the resonator.     

Bidimensional near-field sampling spectrometry

We report on a concept of compact optical Fourier-transform spectrometer based on bidimensional (2D) spatial sampling of a confined interferogram. The spectrometer consists of a nanostructured glass surface on which two light beams interfere in total internal reflection. Subwavelength spatial sampling of the interferogram near field is achieved by introducing a tilt angle between a 2D array of optical nanoantennas and the interferogram pattern. The intensity distribution of the scattered light is recorded on a 2D CCD camera, and a one-dimensional Fourier transform of the interferogram is used to recover the input light spectrum. Experimental results show a wide spectral bandwidth in the visible range, down to 380 nm, with spectral resolution of 1.6 nm around 780 nm.