相位光栅分离双波长宽角度光线的理论分析

使用衍射光栅的分色分光方式一般以平行光入射情况为讨论基础,对于非平行光入射的情况讨论较少.本文基于菲涅尔衍射理论和角谱理论,将球面波与平面波的衍射波场联系起来,从而在传播函数中引入角度参量,结合分数泰伯效应的理论基础,推导出双波长宽角度入射光线经相位光栅衍射后的波场分布函数,并对推导出的函数进行数值模拟,得到像面不同位置衍射波场分布.与平行光入射时的标准波场分布相比较,得到宽角度入射时的衍射波场的横向展宽量和偏移量.通过调节光栅台阶的宽度,改变衍射场的展宽和偏移,使各个单一波长的衍射波场宽度小于光栅周期的一半,从而减少双波长光衍射波场的混叠.同时本文给出波场宽度与光栅台阶宽度的变化关系,选取光栅面上多个位置作为台阶宽度的计算点,并对整个光栅的台阶宽度进行曲线拟合,得到可以使双波长宽角度入射光实现良好空间分离的光栅参量.该结果可用于各类宽角度入射光线的光谱分离场合,如双波长成像、液晶显示和液晶投影等.     

基于表面等离激元的长波QWIP光栅优化

为了提高长波量子阱红外探测器的灵敏度及探测率,采用表面等离激元效应来提高量子阱红外探测器中二维光栅的耦合效率。利用三维时域有限差分算法,分析表面等离激元作用下,长波量子阱红外探测器中二维金属薄膜光栅参数对入射光的调制作用。计算结果表明,对于8 m的入射光,当光栅周期P=2.8 m,孔直径D=1.4 m,光栅层厚度L=0.04 m时,X Y平面内Z方向电场值最大,光栅的耦合效率最高。     

细菌视紫红质的自衍射效率与最佳入射角研究

研究了弱光强下细菌视紫红质膜(bR膜)的自衍射特性.给出了弱光强下相干光在bR膜中产生的振幅光栅光强分布模型,并用ysinαx近似表示透射光强分布,结果与实验吻合.给出了不同透射光强y与指数α的对应关系.结果表明,在bR膜及入射光波波长给定的情况下,入射光强越小,对应的α值越大,当入射光强为0.072/T(mW/cm2)时,α等于1.计算出不同入射光强和入射角下的自衍射效率.结果发现,对应于最大衍射效率的最佳入射角为2°.     

Enhanced surface plasmon interference lithography from cavity resonance in the grating slits

Surface plasmon interference lithography based on grating diffraction has been studied both theoretically and experimentally in recent years. In this paper, we demonstrate that the cavity resonance in the grating slits can improve the subwavelength interference, not only the intensity but also the uniformity of the pattern. Both the typical lithography structure which merely consists of periodic metallic gratings and the modified structure equipped with a reflection layer are studied. The finite element method has been performed to study the interference pattern. Numerical simulations show that the property of the interference pattern is the optimum when cavity resonance happens. This enhancement can be applied to all the lithography structures which are based on the grating diffraction.     

Formation of high-frequency two-dimensional interference patterns of surface plasmon polaritons

The formation of high-frequency two-dimensional interference patterns of surface plasmon polaritons in a structure consisting of four diffraction gratings with one-dimensional periodicity in a metallic film has been studied numerically and experimentally. It has been shown that change of linear polarization of the incident radiation to its circular polarization makes it possible to reduce the period of the formed pattern at a fixed wavelength. A similar change in the form of the pattern can be achieved by introducing an equivalent shift to the geometry of the structure.     

对称面形光栅TE模的衍射特性

本文采用耦合波方法计算了对称面形光栅的衍射效率,分析了光栅截面面形为正弦、三角形、矩形、梯形光栅衍射效率与光栅周期、沟槽深度的关系,计算了光栅的峰值衍射效率。理论计算表明:合理地选择光栅周期、沟槽深度,对称面形光栅都可以达到很高衍射效率,接近100%;光栅的峰值衍射效率基本出现在Bragg衍射且光栅的周期等于衍射波长时。     

低频液体表面波激光衍射条纹的特征

用激光衍射法实现了低频液体表面波稳定、清晰、反衬度非常高的条纹,并发现了缺级现象.理论上分析了表面波的光衍射效应,得到了衍射光场和表面波之间的解析表达式,表达式包括衍射因子和干涉因子.通过对衍射因子和干涉因子的分析,得到衍射条纹空间分布与表面波波长的关系、条纹的半角宽度与入射激光光斑覆盖表面波的个数和入射方向的关系、衍射光强度与表面波振幅的关系,并解释了条纹缺级现象.     

Spin wave diffraction and perfect imaging of a grating

We study the diffraction of Damon-Eshbach-type spin waves incident on a one-dimensional grating realized by microslits in a thin Permalloy film. By means of time-resolved scanning Kerr microscopy, we observe unique diffraction patterns behind the grating which exhibit replications of the spin wave field at the slits. We show that these spin wave images, with details finer than the wavelength of the incident Damon-Eshbach spin wavelength, arise from the strongly anisotropic spin wave dispersion.     

Analysis on diffraction properties of the transmission phase grating

Diffraction properties of the transmission phase grating are analyzed in terms of the Fourier optics theory. The analysis results show that the diffraction intensity distribution of the transmission phase grating is closely related to the optical thickness of the grating and the wavelength of the incident light, and not only determined by the grating's period and slit width. For monochromatic incident light, more than 80% of the diffraction energy will concentrate to the first diffraction order under certain conditions. For white incident light, the energy of the first order of diffraction spectrum may be much higher than other orders. Based on these results, some possible applications of the transmission phase grating are discussed.     

亚波长金属偏振分束光栅设计分析

结合有效介质理论和薄膜光学的抗反射设计方法,设计了基于0.65μm工作波长的亚波长金属偏振分束光栅,给出了光栅的优化设计参数,采用严格耦合波理论分析了光栅的偏振分束特性.结果表明,亚波长金属光栅对TE偏振表现为金属膜特性,具有高反射,对TM偏振表现为介质膜特性,具有高透射,在-30°<θ<30°的大入射角范围和0.47μm<λ<0.80μm的宽入射波谱内,该光栅的透射光和反射光均具有高偏振消光比和低插入损耗的特点. 关键词： 亚波长金属偏振分束光栅 有效介质理论 薄膜光学 严格耦合波理论     

Influence of groove depth and surface profile on fluorescence enhancement by grating-coupled surface plasmon resonance

The fluorescence intensity of a sample placed on a metal grating pattern is enhanced due to excitation by the electric field of the grating-coupled surface plasmon resonance (GC-SPR). The dependence of the enhancement on groove depth and surface profile was studied with the aim of improving the sensitivity of fluorescence detection. The enhancement was found to depend on the groove depth, with intensity most enhanced on grating substrate of about 20 nm depth, which produced an intensity about 30 times greater than that on a flat borosilicate glass substrate. Rigorous coupled wave analysis calculation showed that the shape of the groove influenced GC-SPR, suggesting that controlling not only the depth but also the shape of the grating surface profile can be an important factor in improving the sensitivity of detection by fluorescence microscopy.     

Surface plasmon resonance sensor based on diffraction grating with high sensitivity and high resolution

A surface plasmon resonance (SPR) sensor based on diffraction grating with high sensitivity and high resolution is proposed. The sensitivity of grating coupled SPR sensor based on angular interrogation is enhanced by replacing +1st diffraction order of metallic grating with −1st diffraction order to excite the surface plasmon. To improve the resolution of grating-based SPR sensor, aluminum is used as an SPR-active metal. The reflectivity dip of the Al-based sensor is sharper than an Au-based one, which is the mostly widely used as SPR-active metal. And 3-nm-thick gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the sensor not only has high sensitivity and high resolution, but also exhibits good linearity.     

THz surface plasmon jump between two metal edges

We excite surface plasmon in the THz frequency range at a metal surface using a diffraction grating coupler. Then the excited surface plasmon propagates along the flat metal surface, scatters into free space at the sample edge and then couples onto the flat surface of a second device similar to the emitting one. Using THz time-domain spectroscopy, we study plasmon propagation and its coupling processes in time and frequency domains. We measure a surface plasmon propagation length, at a flat air-aluminum interface, smaller than expected. We report for the first time a high coupling efficiency of the THz surface plasmon field between the two grating devices separated by a several centimeters-thick air gap.     

记录结构对体光栅各向异性衍射选择特性研究

以静态体光栅各向异性衍射理论分析模型为基础,将与体光栅厚度有关的记录光强调制度引入到各向异性耦合波方程中.利用耦合波理论分析了光折变晶体中体光栅的各向异性衍射性能,研究了在不同初始记录光强比的条件下,记录光入射角的改变对光折变体光栅各向异性布喇格衍射性能的影响.结果表明：记录光入射角和记录光初始光强比均对体光栅的各向异性衍射具有选择性;与此相比,记录光入射角和记录光初始光强比对于体光栅各向同性衍射不具备选择性.     

亚波长介质偏振分束光栅的衍射特性

 采用严格耦合波理论并结合矩阵LU分解法,分析了亚波长介质光栅的刻槽深度、占空比、入射角、入射波长等参数对TE偏振和TM偏振0级衍射效率的影响。结果表明:在1 550 nm波长处,出现瑞利反常现象。由此提出利用瑞利反常现象设计工作波长为1 550 nm的偏振分束光栅,通过优化设计确定了最佳设计参数,即光栅周期为l0/2,瑞利入射角为30°,刻槽深为0.9l0,占空比为0.5。结果表明,参数优化后的偏振分束光栅可以使TE偏振0级反射波和TM偏振0级透射波同时达到近100%的衍射效率。     

隐失驻波全内反射荧光显微术的数值计算

从理论上详细计算了在全内反射的条件下，两束入射光产生的隐失干涉场(即隐失驻波)的强度分布，并分析了其不同于传统传播波干涉场的特点。同时使用数值模拟证明了利用隐失干涉场，即隐失驻波的激发方式，可以提高系统的分辨力，在横向实现超经典分辨的荧光成像。具体的分析表明，两束光以相等的角度入射，同时振幅相等，偏振态相同，所形成干涉条纹的反衬度最高，此时成像系统的有效点扩展函数最优化；入射介质1的折射率越大，隐失干涉场的空间周期越短(空间频率越高)，其对应的调制点扩展函数中心瓣的半峰全宽越小，可能分辨更小的物体，但同时旁瓣的强度也增强，最终成像的分辨力受两者的共同制约。     

Resonance excitation of polaritons and plasmons at the interface between a uniaxial crystal and a metal

A resonance is theoretically predicted in which a plane electromagnetic wave in a transparent optically uniaxial crystal, reflected from its metallized surface, creates a wave field at the interface whose intensity is considerably higher than the intensity of the incident wave. In the crystal, a high-intensity (bulk or surface) polariton is excited, whereas, in the metal, a large-amplitude localized plasmon is excited. The structure of the fields created in the crystal is close to that of the fields of bulk polaritons at the boundary with a perfectly conducting surface. The nonideality of the metal is taken into account in the Leontovich impedance approximation. Conditions are found under which the resonance is accompanied by a full transformation of the incident wave into a polariton-plasmon localized near the interface. This coupled wave can be considered as a pumped eigenmode. The intensity of the wave field localized at the boundary can amount to 10–15 times the intensity of the incident wave in the visible range. The resonance half-width with respect to the angles of incidence amounts to a few degrees. In the infrared range, the excitation factor can be an order of magnitude higher, while the resonance half-width sharply decreases down to about 0.1° for a wavelength of 5 μm. Conditions are obtained for the resonance excitation of high-intensity bulk polaritons that arise as reflected modes propagating at a small angle to the boundary. The phenomena investigated are completely attributed to the anisotropy of the crystal.     

Improvement of plasmonic field-matter interaction by subwavelength dielectric gratings

We experimentally and theoretically investigate that detection sensitivity in surface plasmon resonance (SPR) biosensors can be significantly enhanced by employing subwavelength dielectric gratings deposited on a gold film. The enhancement originates from an improvement of field-matter interaction: enhanced evanescent field intensity at the binding region and increased surface reaction area. Using a large-area SiO₂ grating array fabricated by nanoimprint lithography, experimental sensor performance measured by parylene film coating shows that the SPR substrates combined with a dielectric grating provide a notable sensitivity improvement compared to a conventional bare gold film. We also demonstrate that plasmon field can be more confined and enhanced at the dielectric gratings with a larger width. The proposed SPR structure could potentially be useful in a variety of plasmonic applications including high-sensitivity biosensors.     

Multiple beams surface plasmon interference generation: A theoretical analysis

In this paper, multiple beams surface plasmon (SP) interference generation based on prism coupling technique is theoretically analyzed and presented. The proposed multiple beams SP interference configuration is investigated for nanolithography application for two-dimensional feature fabrication. The configuration is then numerically and experimentally analyzed by employing aluminum metal at 364-nm illumination wavelengths to realize high resolution and high aspect ratio two-dimensional periodic nanoscale dot array patterns on the recording medium.     

复合Ag/SiO_2正弦光栅基底SERS特性分析

当前微流控表面增强拉曼散射(SERS)检测领域常用的贵金属纳米颗粒溶胶单位体积内热点区域数量有限且热点区域范围较小,而贵金属纳米三维阵列结构加工时间长,成本高昂并存在"记忆效应"。本文提出了集成到微流道的复合Ag/SiO_2正弦光栅SERS基底结构,可以利用激光干涉光刻技术进行制备,无需预制掩膜版,可实现大面积、低成本SERS基底简易快速制备。利用严格耦合波分析方法(RCWA)建立了复合正弦光栅表面电场增强数学评估模型,推导了表面等离子体共振(SPP)耦合吸收率数学模型,分析了入射光、复合正弦光栅结构与外界环境介电常数的优化匹配关系,得到了入射光785 nm条件下的最佳复合正弦光栅结构。通过制备加工并实验验证了复合正弦光栅的SERS性能,SERS增强因子(EF)能够达到10~4。