微小孔径激光器的研制与近场测试

介绍了一种用于高密度近场存储领域的新型微小孔径激光器(VSAL)。为了解决由腔面金属膜造成的激光器PN结短路的问题,在激光器中引入了窗口隔离区,不仅降低了器件制备的难度,而且也提高了器件的性能和成品率。采用聚焦离子束刻蚀技术成功地制备了输出功率为0 3mW的激光器,利用矩阵方法通过远场测量值估算了激光器的近场分布。     

Feasibility analysis of solid immersion lens-based dual-layer near-field recording optics with a numerical aperture of 1.84

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ_rms and 6.5 mλ_rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.     

Focusing and diffraction by an optical lens and a small circular aperture

Based on the vectorial Rayleigh–Sommerfeld diffraction integrals, analytical expressions for the transversal and axial field distribution of plane waves propagating through a thin lens followed by a small circular aperture are derived and used to study the focusing and diffraction properties of plane waves. Some special cases of our general result are discussed, and illustrative numerical calculation results are given. It is found that the vectorial nonparaxial approach should be applied if the aperture dimension is comparable with the wavelength or the focusing is strong.     

Angular spectrum theory to calculate coupling efficiency in rectangular waveguide resonators

Coupling efficiency of the rectangular waveguide resonators are discussed in terms of the method of angular spectrum theory. Under the condition given in the paper, the coupling coefficients for the EH₁₁ mode in the rectangular waveguide resonator are presented as a function of mirror curvature and position. It is shown that there exist two special geometries to provide low coupling efficiency. The method can be applied to the other modes.     

Nonparaxial diffraction of vectorial plane waves at a small aperture

By using the vectorial Rayleigh diffraction integrals, a nonparaxial propagation equation of vectorial plane waves diffracted at a small rectangular aperture is derived analytically and some special cases are discussed. Numerical calculation results are given to illustrate the applicability and validity of our theoretical formulae. It is shown that for the apertured case the ratio of the aperture width and wavelength affects the beam nonparaxiality. The nonparaxial approach presented in this paper has to be used for diffracted plane waves if the aperture width is comparable with or less than the wavelength.     

Simulation of diffraction from volume holograms

Coupled wave equations that consider two-dimensional distribution and phases of gratings are derived by using weak grating and slow varying approximation. The result of angular selectivity on rand binary data page shows that each minimum is nonzero and each maximum that is not the middle maximum is a little bit smaller than that on plane wave volume hologram. Angular multiplexing is also modeled using the same method, and the middle page is read out in two different angular spacings. The relationship about PSNR versus angular spacing at different multiplexing pages is analyzed to reflect crosstalk between pages. All simulative results show this method is effective for volume holograms simulation.     

谱衍射干涉的计算模拟

本文提出谱衍射干涉的计算模拟方法.着重讨论了谱为几何图案时的干涉现象,得到干涉场强正比于物体沿图案路径的线积分.根据实验观察用二次位相函数来近似模拟酒精灯火焰的位相延迟,相应计算了几种特殊谱分布的衍射干涉强度分布,得到与实验相一致的结果.本文还讨论了几种特殊谱衍射干涉的特点,得到了一些结论.     

圆孔的菲涅耳衍射

得到了圆孔菲涅耳衍射光强分布的表达式,此式由贝塞尔函数的数列(或Lommel函数)给出,因此很容易利用普及的数学软件算出结果.并且利用CCD照相机量度了衍射光强分布,与运算的结果作了比较,也与Burch在1985报导的结果作了比较.     

透射式矩形相位光栅的衍射光谱分析

提出了一种计算透射式矩形相位光栅衍射场的简便方法,计算并分析了透射式矩形相位光栅的衍射光谱,给出了相位光栅的衍射光谱与光栅材料的折射率、光栅厚度和入射波长的关系,得到了把衍射光能量集中到1级光谱的条件;并在相位光栅的应用方面作了探讨.     

Super-transmission of light through subwavelength annular aperture arrays in metallic films: Spectral analysis and near-field optical images in the visible range

This paper presents experimental studies of the enhanced light transmission through metallic films pierced by subwavelength annular apertures. Two different methods (e-beam lithography and focused ion beam) have been used to build the nano-structures. We have experimentally recorded their far-field spectral response in the visible range and the optical near-field above the nano-structures when they are excited at 633 nm. The spectral response exhibits a transmission peak at 700 nm with maximum efficiency around 16%. The near-field exhibits a characteristic two-lobe structure just above the aperture. Finite difference time domain (FDTD) simulations reproduce quite well the experimental results.     

Near-field properties of diffraction through a circular subwavelength-size aperture

Analytical nonparaxial vectorial electric field expressions for both Gaussian beams and plane waves diffracted through a circular aperture are derived by using the vector plane angular spectrum method for the first time,which is suitable for the subwavelength aperture and the near-field region.The transverse properties of intensity distributions and their evolutions with the propagating distance,and the power transmission functions for diffracted fields containing the whole field,the evanescent field and the propagating field are investigated in detail,which is helpful for understanding the relationship between evanescent and propagating components in the near-field region and can be applied to apertured near-field scanning optical microscopy.     

The rigorous electromagnetic theory of the diffraction of vector beams by a circular aperture

The rigorous electromagnetic theory of the diffraction of vector beams by an aperture is proposed and numerically evaluated by the diffraction of vector Gaussian beams by a circular aperture. The results are compared with those, by using the vector Rayleigh–Sommerfeld diffraction integrals and angular-spectrum expression theory, showing a good consistency. The numerical calculation shows that the result calculated by the rigorous theory is much more precise than those calculated by the integral method in diffraction near field, and a highly consistency reaches by the three methods in diffraction far field. A further extension of the theory is discussed.     

Research on a fast algorithm of three-dimensional CGH

This paper puts forward a novel fast algorithm of three-dimensional Computer-Generated Hologram (CGH). The algorithm proposed can directly express the two-dimensional Fourier spectrum of a unit square by an analytic function, as well as the light field distribution of the unit square on the holographic plane (the unit square is not parallel to the holographic plane). The computer simulation and photoelectric reconstruction are also performed to verify the algorithm. The experimental results show that the algorithm is quick and simple, providing a good reference to research on three-dimensional CGH.     

高斯光束照射下与矩孔相关的孔径衍射

依据基尔霍夫衍射理论,利用幂级数展开的方法,推导出傍轴条件下高斯光束的矩孔及单缝衍射的近似计算公式,并通过数值计算、数值模拟等方法对衍射场的基本特性进行了讨论。     

Modeling of near-field optical diffraction from a subwavelength aperture in a thin conducting film

A theoretical model, novel to our knowledge, to investigate the near-field optical diffraction from a subwavelength aperture in a thin conducting film is presented. A governing equation for the magnetic field distribution in an optical thin film based on the power flow theorem is derived for the first time. Thus all of the components of the electric and magnetic fields inside or outside the thin film with a subwavelength aperture embedded can be obtained by applying the Hankel transform accurately. Numerical computations are performed to illustrate the edge effect by an enhancement factor of 2.2 and the depolarization phenomenon of the transmission in terms of the distance from the film surface.     

Geometrical theory of diffraction

Geometrical theory of diffraction (GTD) is an alternative model of diffraction propounded first by Thomas Young in 1802. GTD has a long history of nearly 150 years over which many eminent people enriched this model which has now become an accepted tool in the calculation of diffraction patterns. In the conventional Helmholtz-Kirchhoff theory the diffracted field is obtained by computing the net effect of the waves emitted by all points within the area of the aperture. But GTD reduces this problem to one of computing the net effect of waves from a few points on the boundary of the aperture or obstacle, thus simplifying considerably the labour involved in computations. Also the theory can easily be modified to include polarization effects. This has been done specifically by Keller (1962) who exploited the Sommerfeld solution of diffraction of electromagnetic waves at a half plane, making the theory more versatile than the Kirchhoff scalar wave theory. Interestingly the geometry of difffracted rays is predictable from a generalized Fermat principle. According to this the total path chosen by light from the source to the point of observation via the diffracting boundary is an extremum. Historically it should be stated that many of the salient features of GTD were established by a school led by Raman which was active from 1919–1945. Later when Keller (1962) revived GTD independently, he and others who followed him rediscovered many of the results of the Raman school. We have stressed wherever necessary the contributions of the Indian School. We have also discussed certain geometries where GTD can be effectively used. We get some new and interesting results, which can be easily understood on GTD, but are difficult to interpret on the conventional theory of diffraction.     

Angular dispersive diffraction using a diamond-anvil pressure cell and synchrotron X-ray source

Abstract

Wavelength dispersive diffraction studies have been performed using a diamond-anvil pressure cell and bending magnet synchrotron produced radiation. A double-crystal monochromator was used to select 15 and 17 keV photons and a 80 μm diameter collimator was used to restrict the beam entering the pressure cavity. Parallelism between the incident beam and the collimator axis was assisted by computer control of the collimator. The image of the transmitted beam was observed using a Hamamatsu x-ray Vidicon and TV monitor, for this alignment. The diffracted beam was recorded on x-ray film using a double film cassette and exposure times ranged from 6 to 8 hours. Neither the exposure time nor the line width of the diffraction lines was significantly altered by replacement of the incident beam collimator with a slit system.     

X射线衍射进展简介

100年前,劳厄等证明X射线对硫酸铜晶体具有衍射能力,揭开了X射线衍射分析晶体结构的序幕.100年的发展,X射线衍射已经成为自然科学乃至医学、考古、历史学等众多学科发展的必备技术.文章介绍了X射线衍射现象的发现历史,X射线运动学和动力学理论的发展概况,并举例说明了X射线衍射在粉末多晶体、单晶体和人工功能晶体以及人工薄膜材料中的具体应用情况,最后简要展望了X射线衍射技术的发展前景.