Optical transmission enhancement by a sub-wavelength film lens

A new sub-wavelength metallic film lens configuration is proposed, which is embedded in a thin ideal metal film, and its near field optical properties arc investigated by finite-difference time-domain (FDTD) method. It is found that the optical transmission is greatly enhanced, and the spot size can be reduced by the sub-wavelength metallic film lens in comparison with the bare aperture. This kind of lens is expected to have practical applications in the very small aperture laser (VSAL), a promising nanosource for near-field optical storage and lithography.     

Analysis of transmittance enhancement for a slab lens formed by sub-wavelength holes array on the metallic film

By investigating the transmittance and phase characteristics of the square holes on the metallic film, we find that the transmittance fluctuates with center distance between holes and appears resonant peaks, which attributes to the surface wave enhanced transmission phenomenon while the corresponding phase retardation through holes keeps constant. Based on this phenomenon, the slab lens can be optimized to a high transmittance by modulating the center distance of the holes. Design results show that the light intensity values at the focal spot of the slab lens can be enhanced from 3 to 14.5 in intensity scale when the center distance changes from 1.25λ to 0.95λ.     

Rigorous transmittance analysis of a sub-wavelength Sb thin film lens

We quantitatively analysed the factors contributing to the optical transmission enhancement of a sub-wavelength Sb thin film lens, using the finite-difference time-domain (FDTD) method. The results show that the transmission enhancement of the dielectric with a Gaussian distributed refractive index loaded in a sub-wavelength circular hole is not only due to the high refractive index dielectric, but also due to the specific distributions of refractive index. It is the first study about the effects of the refractive index distribution on the transmission of a sub-wavelength aperture. This kind of lens has practical applications in the very small aperture lasers and for near-field optical storage and lithography. PACS 42.79.Ag; 42.25.Bs; 42.25.Fx     

Optical absorption by surface plasmons in deep sub-wavelength channels

The interaction of visible light with surface plasmons in a periodic array of silver channels is studied experimentally and theoretically. Channels of width 130 nm and depth 280 nm on a pitch of 468 nm were fabricated using electron beam lithography. Measurements of the reflectance of the channels show strong absorption for a specific angle of incidence at a given wavelength of the light. It is shown using a simple geometric model that this is consistent with the excitation and propagation of surface plasmons in the deep sub-wavelength channels. A numerical simulation of the electromagnetic fields excited in the channels confirms this result.     

Image transmission by a Bragg-Fresnel X-ray lens

A periodic grid image transmission by a Bragg-Fresnel lens (BFL) in a twice reduced scaled scheme has been carried out. The experiments have been performed in white synchrotron radiation in a hard spectral region (λ≈1 Å).     

亚波长孔阵列的太赫兹波异常透射研究

利用太赫兹时域光谱（THz-TDS）系统,在5—300 K温区下测量了在厚度约200 nm的金属Nb薄膜刻蚀的亚波长圆孔阵列的异常THz波透射情况.实验结果表明,在03—2 THz波段,具有亚波长孔阵结构的金属Nb薄膜的异常透射现象波谱的峰位置与CST（computer simulation technology）软件仿真模拟的结果一致,峰值随温度降低有逐渐增强的趋势. 关键词： 亚波长孔阵列 THz时域光谱技术 异常透射     

Optical transmission loss in tin oxide thin film waveguide

This paper reports the optical transmission loss of tin oxide thin film waveguide. The effect of oxidation temperature, thickness and air ageing (40 days at room temperature) was studied. The vapour chopping technique has been used successfully to reduce the optical transmission loss. The vapour chopped tin oxide thin film waveguide (2.90-3.60 dB/cm) showed smaller transmission loss than those of nonchopped tin oxide thin film waveguide (4.16-4.74 dB/cm). Transmission loss was found to be a function of oxidation temperature and thickness. Due to increased oxidation temperature, transmission loss was found to decrease. The effect of increase in thickness was to increase the transmission loss. The air ageing effect caused the increase in transmission loss whereas the effect was found lesser in the vapour chopped tin oxide thin film waveguide.     

Enhanced and confined light transmission through a funnel-type aperture with a sub-wavelength outlet

Enhanced transmission through sub-wavelength hole arrays and a single sub-wavelength aperture with periodic corrugations surrounded have been investigated extensively. We report the similar phenomenon through a funnel-type aperture with a sub-wavelength outlet in a thick silver film, which was obtained numerically by using finite-difference time-domain method. Properties of the transmission spectrum can be modulated by geometric parameters of the funnel-type aperture. With periodic grooves or dielectric gratings on the output surface of the structure, beaming light emission can be obtained.     

二维亚波长金属小孔阵列的透射光增强效应

对金属薄膜上的二维亚波长小孔阵列的光透射增强现象进行了数值模拟，结果显示不仅实际金属薄膜上的小孔阵列结构具有透射增强效应，理想导体薄膜的相同结构也具有透射增强效应，但没有实际金属薄膜的增强明显-通过分析指出，这种小孔阵列的光透射增强效应是一种复杂的波导耦合效应-与金属薄膜上的表面电流一样，表面等离激元波具有将入射光能量从金属表面向小孔转移的作用，但不是透射增强的本质原因- 关键词： 表面电流 共振耦合 透射增强 表面等离激元     

Optical transmission properties and enhanced loss for randomly positioned apertures in a metal film

The transmission of light through randomly distributed rectangular apertures in a gold film on glass substrate is calculated for the first time. The results for randomly distributed apertures, when compared with the transmission resonance through a single aperture, show the new features of a peak reduction, a blue-shift and the appearance of ripples. Only the latter of these features has been reported previously. The loss from the isolated aperture is compared with the loss from the randomly distributed apertures to show how coupling between apertures enhances the loss in the presence of a lossy metal film. PACS 81.07.-b; 71.36.+c; 78.66.Bz; 42.25.Dd     

1D Bessel-like beam generation by highly directive transmission through a sub-wavelength slit embedded in periodic metallic grooves

A new method to generate a quasi-one dimensional (1D) Bessel-like beam whose non-diffracting length extends to macroscopic scale is proposed by utilizing highly directive transmission through a sub-wavelength single slit embedded in periodic metallic grooves. We employed finite-difference time-domain methods for full-vectorial diffraction and spectral analysis. In optimal conditions, unique quasi-1D Bessel-like beams were generated in transmission for the incident p-polarized plane wave such that highly asymmetric far-field distribution was achieved; Bessel-like beam along the slit axis and a flat-top super-Gaussian beam along the other perpendicular axis. Detailed parametric studies for the proposed structure are reported in terms of the operating spectral range and a general window of optimal conditions.     

Generation of sub-wavelength and super-resolution longitudinally polarized non-diffraction beam using lens axicon

It is well known that a light spot of sub-wavelength will diverge in all directions. In this letter, A method is presented for generating sub-wavelength (0.44λ) longitudinally polarized beam, which propagates without divergence over lengths of about 2λ in free space. This is achieved by a high numerical aperture (NA) lens axicon that utilizes spherical aberration to duplicate the performance of an axicon and to create an extended focal line.     

Optical transmission and reflection of aluminum film irradiated by nanosecond laser beam and experimental studying of phase-explosion

In this paper we present evidence for a phase explosion during the laser-induced ablation process by studying the optical reflectivity of the ablated plume. The ablation was produced by irradiating thin film aluminum coated on a quartz substrate with a single pulse laser beam in ambient air. The laser pulse was provided by the second harmonic of a Q-switched Nd:YAG laser with ∼10 ns pulse duration. The transmission of a low power He–Ne laser beam through the hot ablated material plume and its reflection (from the front surface, and rear surface of aluminum film) were also monitored during the duration of the ablation event. The results show that the front surface reflectivity is enhanced at an early time of ablation which is described as strong evidence for the creation of a phase explosion in this process.     

亚波长周期性各向异性金属薄膜的等离子体共振特性

基于各向异性模型,运用全矢量的3维时域有限差分法（FDTD）,研究了在外磁场作用下,亚波长周期性各向异性金属薄膜的表面等离子体共振机制和特性,即由周期性穿孔形成的局域波导共振和由周期性结构引起的光子晶体共振效应。研究发现:当薄膜厚度一定时,两种等离子体共振模式都会随着外磁场的增大而向短波方向移动;而当外磁场一定、薄膜变厚时,周期结构因素引起的共振传输峰向长波方向转移,波导共振传输峰向短波方向转移;通过调控外加磁场的大小或方向可控制光通过金属薄膜的增强传输效应。     

亚波长周期性各向异性金属薄膜的等离子体共振特性

 基于各向异性模型,运用全矢量的3维时域有限差分法（FDTD）,研究了在外磁场作用下,亚波长周期性各向异性金属薄膜的表面等离子体共振机制和特性,即由周期性穿孔形成的局域波导共振和由周期性结构引起的光子晶体共振效应。研究发现:当薄膜厚度一定时,两种等离子体共振模式都会随着外磁场的增大而向短波方向移动;而当外磁场一定、薄膜变厚时,周期结构因素引起的共振传输峰向长波方向转移,波导共振传输峰向短波方向转移;通过调控外加磁场的大小或方向可控制光通过金属薄膜的增强传输效应。     

Structured lens formed by a 2D square hole array in a metallic film

A method is proposed to modulate phase using variant square holes in a metallic film based on a fundamental mode approximation model. Phase retardation through square holes in a subwavelength scale in a thin metal film has been analyzed and calculated. Based on the model, a structured lens with a numerical aperture of 0.583 and a focal length of 240 microm formed by a 2D square hole array in a metallic film is designed. Numerical simulation using the finite-difference time-domain method is carried out, and the results agree with the theoretical analysis. A focal spot close to the diffraction limit can be obtained.     

光学树脂防护眼镜片

介绍光辐射对人眼的危害和损伤的三种类型,对几种光学树脂防护镜片的特性亦简要阐述。     

Extraordinary light transmission through a metal film perforated by a subwavelength hole array

It is shown that, depending on the incident wave frequency and the system geometry, the extraordinary transmission of light through a metal film perforated by an array of subwavelength holes can be described by one of the three mechanisms: the “transparency window” in the metal, excitation of the Fabry–Perot resonance of a collective mode produced by the hybridization of evanescence modes of the holes and surface plasmons, and excitation of a plasmon on the rear boundary of the film. The excitation of a plasmon resonance on the front boundary of the metal film does not make any substantial contribution to the transmission coefficient, although introduces a contribution to the reflection coefficient.     

Real-time enhancement of defects in periodic patterns by use of a bacteriorhodopsin film

We present a real-time optical system to enhance defects in periodic patterns by use of nonlinear spatial filtering by real-time holography. A straight and equispaced grating written in a bacteriorhodopsin film is read by the Fourier transform of a periodic pattern to be inspected. Because the diffraction efficiency of the grating depends on the intensity of the reading beam, only the defect component can be selectively diffracted and imaged. This system is applicable even to moving objects. We present experimental results that show enhancement of defects as small as 10 microm in a photomask with a pixel pitch of 150 microm used for a liquid-crystal display.