散射介质中层间杂质检测效率的影响因素及分析

散射介质中层间杂质检测是一个非常重要的研究课题.改进现有的Monte Carlo方法,模拟大量光子在散射介质中的传输,得到入射光强、杂质埋藏深度、介质折射率、介质散射系数和各向异性因子对光学透反射成像法检测层间杂质效率的影响规律.结果表明,入射光强、杂质埋藏深度和介质折射率对透反射成像检测结果均有影响,且影响规律相似.增加入射光强、减小杂质埋藏深度或减小介质折射率均可提高反射光成像的检测效率;增大入射光强、减小介质折射率、减小介质散射系数或增大各向异性因子均可提高透射光成像的检测效率.这些规律对散射介质中层间杂质检测具有一定指导意义.     

超半球形固体浸没透镜系统的亚表面显微

应用矢量衍射理论和薄膜光学方法,研究了有禁带存在时超半球形固体浸没透镜(SIL)系统的亚表面显微。模拟计算结果显示,光斑的强度,边瓣强度和光斑大小随禁带厚度发生振荡。光斑的大小和光斑的强度几乎是反相变化的。当禁带材料的折射率与固体浸没透镜(SIL)的折射率相匹配时,光斑的强度较大,分辨率较高。随着离开样品表面的距离的增加,光斑的强度不断减小,光斑的大小和边瓣强度逐渐增加。     

改变光子晶体表面结构对负折射透射光强的影响

以砷化镓圆形介质柱在空气中构成二维六边形排列结构的光子晶体为例,利用时域有限差分法模拟研究了光子晶体表面结构改变对负折射透射光强的影响.模拟结果表明：针对同一结构光子晶体,在可产生负折射现象的入射光频率范围,改变光子晶体表面两侧圆形介质柱的半径和顺向侧移两侧表面最外层圆形介质柱都会均对负折射透射光强产生影响.     

改变光子晶体表面结构对负折射透射光强的影响

以砷化镓圆形介质柱在空气中构成二维六边形排列结构的光子晶体为例,利用时域有限差分法模拟研究了光子晶体表面结构改变对负折射透射光强的影响.模拟结果表明:针对同一结构光子晶体,在可产生负折射现象的入射光频率范围,改变光子晶体表面两侧圆形介质柱的半径和顺向侧移两侧表面最外层圆形介质柱都会均对负折射透射光强产生影响.     

折射率梯度表面机理的研究

本文构建了一种折射率梯度表面,并利用几何光学法对其物理机理作了研究,发现这种折射率梯度表面可以实现入射波到正常反射波,异常反射波,以及介质波的转换.当入射点介质折射率大于某一阈值时,异常反射波束方向角正弦值与入射波束方向角正弦值存在线性关系,意味着平行入射的波经介质后将平行出射到空气;而当折射率梯度常数大于某一阈值时,任何方向入射的波在透射到介质后,将发生全反射,被束缚在介质中.总而言之,通过调节结构参数,可以实现对波束方向与强度的人工调控,从而提供了一种人工可控的全介质梯度表面的工程实现思路.     

关于折射率对散射光场分布影响的研究

根据Mie散射理论,采用理论计算和实验相结合的手法,研究了光散射现象以及散射介质的折射率对散射光场分布的影响.通过对空气中不同折射率的散射介质形成的散射光场光强的实验比较,论证了散射介质折射率的实部变化对散射光强的影响不大,其主要影响是通过对相位的变化来实现的,也即散射介质折射率的虚部变化对光强的影响很大,在实际应用中不可忽略.这一结论对以散射光场的分布为基础的各种研究具有一定的指导意义.     

涂有半导体气敏薄膜的长周期光纤光栅气敏传感特性理论分析

首先利用耦合模理论研究了长周期光纤光栅LPFG折射率敏感特性,数值计算了长周期光纤光栅透射谱谐振波长与环境介质折射率的关系。其次分析了半导体氧化物气敏膜光学特性机理,当气体与薄膜接触时,气体会使敏感膜的消光系数、吸收系数和相应的折射率发生变化。基于上述两点,提出可将气敏膜涂于光栅表面,利用气敏膜的折射率随环境气体成分和浓度变化而变化的特性,从而影响LPFG透射谱谐振波长的变化,通过检测波长的变化达到探测气体成分和浓度的目的。由于长周期光纤光栅对环境介质折射率的灵敏度高于光纤,且其传感信号属于波长调制,测量信号不受光强波动及光纤损耗的影响,因此其灵敏度比强度型光纤气体传感器高。     

部分相干平顶光束在梯度折射率介质中的传输特性

利用广义惠更斯-菲涅尔衍射积分方法,推导出部分相干平顶光束在梯度折射率介质中传输的交叉谱密度函数解析表达式,对部分相干平顶光束在梯度折射率介质中的传输特性进行了分析,并进一步讨论了介质梯度折射率系数、光束阶数以及光束相干性对传输特性的影响.结果表明,部分相干平顶光束在梯度折射率介质中传输时的轴上光强分布呈现周期性变化了,且周期由梯度折射率系数决定,而与光束相干性无关.光束阶数越高、相干性越好、介质梯度折射率系数越大,则在介质中的轴上峰值光强越大.并且,在光强峰值位置附近的光强分布随传输距离的变化非常剧烈.     

非线性一维光子晶体反射谱的多值特征研究

以含有一层kerr非线性介质的一维光子晶体为对象,基于子层逆向递推算法,给出了非线性反射谱一种简单有效的数值计算方法.基于此方法得到了该结构在1 535~1 565nm范围内的非线性反射谱.当输入光强高于阈值时,缺陷模缓慢移动并出现弯曲倾斜的多值特征.分析了上跳波长、下跳波长随输入光强的变化趋势.研究了线性周期介质和非线性介质结构参数对反射谱的影响.研究表明:增加周期介质的周期、高低折射率比和非线性层厚度都能使缺陷模变窄,输入光强阈值和上跳波长、下跳波长的阈值波长降低;而非线性介质的三阶非线性系数增大时,输入光强阈值降低,但缺陷模宽度、上跳波长和下跳波长的阈值波长没有明显改变.这种多值特征对于设计光学开关、光学滤波器等有着重要的指导作用.     

平顶高斯光束在梯度折射率介质中的传输特性

 利用广义惠更斯-菲涅耳衍射积分法,推导出平顶高斯光束在梯度折射率介质中传输时的解析表达式,对平顶高斯光束在梯度折射率介质中的传输特性进行了分析,讨论了介质梯度折射率系数和光束阶数对传输特性的影响。研究表明,平顶高斯光束在梯度折射率介质中传输时轴上光强分布呈现周期性变化,其周期决定于介质梯度折射率系数,而与光束的阶数无关;轴上峰值处的横向光强分布受梯度折射率系数和光束阶数的影响较大,横向光强的最大值随着梯度折射率系数的增大而增大。     

Multiple reflection effect inside a hemispherical solid immersion lens

The reflection inside a hemispherical solid immersion lens (h-SIL) is analyzed by using the film-interference optics and the new unique characteristic of the h-SIL is presented. The image theory of SIL microscopy is developed. Numerical results show that the reflection inside the h-SIL, especially for large mismatch in refractive indices between the SIL and the medium, has an important influence on the resolution of SIL surface microscope and the collection efficiency from the emitter. Theoretical and experimental results are compared through three examples, the reflection-mode microscope, the transmission-mode microscope, and the collection of light from the emitters. The present theoretical values are quite consistent with the experimental values in SIL microscopy. It is of interest to note that owing to the interference in the SIL, the resolution and collection efficiency periodically oscillate with the radius of an h-SIL, which mean that the radius of an h-SIL has to be well-controlled to achieve enough high resolution and collection efficiency.     

Dispersion effect in optical microscopy systems with a supersphere solid immersion lens

This paper studies the dispersion effect of the supersphere solid immersion lens (SIL) on a near field optical microscopy system by using the vector diffraction theory. Results show that when a real non-monochromatic beam illuminates a supersphere SIL microscopy, the dispersion effect of the SIL has an important influence on the image quality. As the wavelength bandwidth of the non-monochromatic beam increases, the size of the focused spot increases and its intensity decreases in near-field microscopy systems with a supersphere SIL.     

Laser-tweezer-controlled solid immersion microscopy in microfluidic systems

We describe the creation and implementation of a near-field scanning solid immersion microscope that is specifically tailored for use in microfluidic systems. The microscope comprises a newly fabricated Weierstrass solid immersion lens (SIL), which is detached from its substrate and is free floating in the fluid, and a laser optical tweezer, which serves both as a trapping beam for alignment and positioning of the SIL and as a near-field scanning beam that images the sample through the SIL. A discussion of the SIL's fabrication method is presented along with experimental results that demonstrate the effectiveness of our microscope design.     

Optimizing the optical field distribution of solid immersion lens system by a continuous phase filter

In solid immersion lens (SIL) microscopy systems with high numerical aperture (NA), there always exists the aberration produced by Fresnel effects at the interface between SIL and the sample. This aberration may cause the degradation of the image of sample. We design a continuous phase filter and optimize the optical field distribution of SIL system. The numerical results show that when the continuous phase filter is used, the field distribution of SIL system can be optimized, and the focal depth and intensity of transmitted light can be increased. At the same time, the intensity of side-lobe and the resolution are kept almost unchanged.     

FDTD方法对固体浸没透镜的光场分析

采用二维时域有限差分(2D-FDTD)方法研究了高斯光束通过固体浸没透镜(SIL)的光场分布特性.模拟结果表明,SIL的折射率越大,底面出射的光斑越小,但随离底面距离的增大光束很快展宽;当只有入射角大于全反射临界角、具有高空间频率的部分高斯光束聚焦到SIL底面金属膜中心的微孔时,针对不同直径的微孔,模拟了出射光场的分布,发现微孔直径在某一特定值时,出射光斑半径在距SIL底面近半个波长范围内无明显改变,该结果为增大SIL和存储介质间距的方案提供了理论依据.     

Refractive and reflective behavior of polymer prisms used for surface plasmon guidance

Two-dimensional optics with surface plasmons was realized by the use of topographically structured dielectric polymer coatings. Triangles of polymethylmetacrylate (PMMA) with lateral dimensions of some tens of micrometers on top of a silver layer act as two-dimensional prisms for surface plasmons. Refraction and internal reflection of plasmons were investigated by scanning near-field optical microscopy. The change in propagation direction can be explained by Snell's law when taking an effective refractive index for plasmons into account. Furthermore, intensity modulations in the PMMA elements and in the transmitted plasmon beam were observed.     

Realization of a subwavelength focused spot without a longitudinal field component in a solid immersion lens-based system

In a solid immersion lens (SIL)-based system, we predict theoretically that, by using the illumination of an azimuthally polarized beam with helical phase (APH), the subwavelength focusing can be simultaneously realized both in SIL and the third medium in spite of the presence of an air gap between the SIL and the third medium, which is not easily achieved in the case of the illumination of linearly, circularly, and radially polarized beams. For the APH illumination, the field in the focal region of the multilayered medium has no longitudinal component, and the on-axis intensity of the focused spot is nonzero. The APH illumination extends the capacity of SIL in realizing a supersmall focused spot, which is useful in microscopy, near-field optics, recording optics, and lithographic optics.     

Angle-dependent infrared absorption spectroscopy at electrode/electrolyte interfaces

Angle-dependent internal reflection spectroscopy is performed in the attenuated total reflection setup for an electrochemical cell with a Fourier transform infrared spectrometer. The working electrode is a thin Pt film evaporated onto a hemispherical Si prism. The refractive index of the Pt film obtained from the experiment is found to differ from the value for bulk material. The difference is ascribed to the surface corrugation of the Pt surface and the film thickness in the nanometer range. The function of reflection intensity versus angle of incidence changes significantly when a resonant absorption occurs in the electrolyte medium. The angle-dependent absorption band intensity of CO adsorbed on the Pt film under potential control reveals changes in magnitude and an inversion of the band for different angles of incidence. This behaviour is explained by the excitation of resonant surface plasmon waves at the Pt/electrolyte interface and by multiple reflections occurring at the interfaces. A simulation for the three-layer system Si/Pt/electrolyte agrees with the experimental results.     

附加球面相位引致Airy光束在单轴晶体传输时的两次镜像演化

利用单轴晶体光束传输理论,求得了具有附加球面相位Airy光束在单轴晶体中的传输公式.数值模拟计算结果表明,线偏振附加球面相位Airy光束在晶体中传输时仍为线偏振,但不是传输不变的.粗略地讲,具有附加球面相位的Airy光束在晶体中传输时,近场是传输不变的;而在由晶体寻常与非寻常折射率和球面半径共同确定的两个特定传输距离处,传输光束转换成了取向不同的Gaussian-Airy光束,且高斯依赖的束宽度敏感地与截断因子相关;而当光束依次穿过此两位置时光斑花样先后相对于两横向轴平面做镜像演化,且镜像演化顺序也与晶体寻常和非寻常折射率相对大小密切相关,其总的效果是远场强度花样能恢复原样但花样取向产生了关于对过横平面二、四象限平分平面的镜像演化.这些结果表明,通过恰当选择晶体材料(即折射率)和附加球面相位的半径R,可以调控光束花样的形状、取向及表征各向异性材料的相关性质.