Acoustically modified optical Fresnel diffraction by a slit and a periodic object in relation to periodic partial coherence

Optical Fresnel diffraction by a slit and a periodic rectangular wave object, illuminated with accoustically phase-modulated laser light, is investigated in association with partial coherence. The periodic partial coherence, produced by acousto-optic interaction, much deformes the Fresnel diffraction patterns of the respective objects. A nearly flat-top diffraction pattern by the slit is obtained if the acoustic and slit parameters are adjusted. The self-image by the periodic rectangular wave object is reversed in contrast if the acoustic power exceeds a critical value.     

Influence of slit width on the electromagnetic transmission of a periodic metallic grating

The light transmittance of a periodic metallic grating with varied slit widths has been investigated. The transmission peaks move to the shorter wavelength direction with an increase in the width of slits while keeping the other parameters unchanged. It was demonstrated that the slit width affects the spectral transmittance of the metal grating significantly. It was also found that the effective refractive index and cavity modes in slits are responsible for this phenomenon. Cavity modes play an important role in extraordinary transmission of the sub-wavelength aperture grating. When a complete resonant mode forms in the slits, a high transmission will appear. A wider slit results in a smaller efficient refractive index and thus affects the cavity mode in the slits. These two elements cause the transmission peaks to move to the shorter wavelength direction with widening of slits. The results obtained here may provide a useful guide to design metallic slit grating devices.     

Flat-topped spectrum obtained from partially coherent hollow Gaussian Schell-model beams passing through a slit

The anomalous spectral behaviors of partially coherent polychromatic hollow Gaussian Schell-model beams (HGSMBs) diffracted by a slit are investigated. Besides spectral switches, asymmetrical dual-peak spectral split and multi-peak spectral split are observed. In the vicinity of the positions where spectral switches occur, flat-topped spectrum can be obtained, the bandwidth of which is adjustable by changing the transverse coherence width and the observation position. The flat-topped spectrum has potential application for creating probe beams in optical metrology systems and generating broadband optical sources in fiber optic sensor interface systems.     

基于塔姆激元-表面等离极化激元混合模式的单缝加凹槽纳米结构的增强透射

金属单缝纳米结构因为结构简单、易于集成,常用在基于表面等离极化激元(surface plasmon polaritons,SPPs)的纳米结构中构建光源.但是,金属亚波长单缝结构一直存在透射率低的问题,如何提高其透射率一直是研究的重点.为了更好地提高金属亚波长单缝的透射率,本文对之前文献提出的分布式布拉格反射镜(distributed bragg reflector,DBR)和金属银薄膜纳米缝结构进行改进,在金属银薄膜两侧设计凹槽.当TM偏振光由DBR侧入射至DBR-银纳米缝结构时,DBR-银膜界面上和银膜入射侧凹槽一起激发的塔姆激元(Tamm plasmon polaritons,TPPs)和SPPs,以及纳米缝和银膜出射侧凹槽对的SPPs同时激发,利用凹槽激发的SPPs和银膜表面处的TPPs-SPPs混合模式的干涉相长耦合作用,通过塔姆激元的局域场增强效应和两侧凹槽与单纳米缝的干涉相长耦合作用进一步提高了表面等离极化激元模式的激发效率,再加上纳米缝中的类法布里-珀罗腔共振效应,使纳米缝的透射率得到增强.本文采用有限元方法研究了DBR-银纳米缝结构上单纳米缝加凹槽的透射特性.经过一系列参数优化,使DBR-银纳米缝凹槽结构的最大透射率增加到0.22,相对于TiO_2-银纳米缝结构的透射率(0.01)提高了22倍,比文献[23]得到的最大透射率0.166有所提高.研究结果在纳米光源设计、光子集成电路和光学信号传输等相关领域具有一定的应用价值.     

Tunable directional beaming assisted by asymmetrical SPP excitation in a subwavelength metallic double slit

We present a design for tunable directional beaming through a subwavelength metallic double slit surrounded by dielectric surface-relief gratings.On-axis and off-axis beaming can be switched by controlling the incident angle to asymmetrically excite surface plasmon polaritons(SPPs) that are subsequently coupled out to propagating beams by the two gratings on the left and the right sides of the double slit.Furthermore,the division of optical power into two off-axis beaming directions can be tuned smoothly by varying the incident angle while keeping the total power almost unchanged.The mechanism of this effect is analyzed theoretically and verified using rigorous numerical simulations.     

Optical control over surface-plasmon-polariton-assisted THz transmission through a slit aperture

We demonstrate optical control over the transmission of terahertz (THz) radiation through a single subwavelength slit in an otherwise opaque silicon wafer. The addition of periodic corrugation on each side of the wafer allows coupling to surface plasmon polaritons, so that light not impinging directly on the slit can contribute to the transmission. A significant enhancement of the THz transmission can be achieved through control of the surface wave propagation length by excitation at optical wavelengths. The observed transmission increase is in distinct contrast to the reduction reported for photoexcitation of arrays of holes in semiconductors.     

An explanation of interference effects in the double slit experiment: Classical trajectories plus ballistic diffusion caused by zero-point fluctuations

A classical explanation of interference effects in the double slit experiment is proposed. We claim that for every single “particle” a thermal context can be defined, which reflects its embedding within boundary conditions as given by the totality of arrangements in an experimental apparatus. To account for this context, we introduce a “path excitation field”, which derives from the thermodynamics of the zero-point vacuum and which represents all possible paths a “particle” can take via thermal path fluctuations. The intensity distribution on a screen behind a double slit is calculated, as well as the corresponding trajectories and the probability density current. The trajectories are shown to obey a “no crossing” rule with respect to the central line, i.e., between the two slits and orthogonal to their connecting line. This agrees with the Bohmian interpretation, but appears here without the necessity of invoking the quantum potential.     

Position sensor based on slit imaging

A position sensor based on slit imaging is proposed and its measurement principle is described.An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system.A magnified image of the detection double slit is formed on a bi-cell detector.The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector.In experiments,the feasibility of the sensor was verified.The repeatability was less than 40 nm.     

Enhanced optical transmission through a subwavelength 1D aperture

We present finite difference time domain simulations of the enhancement of the optical transmission through a single subwavelength slit in a thick metal film caused by resonances of the electromagnetic fields in and near the slit. These can be enhanced by including a periodic modulation on the in-coupling surface, and the dependence of the transmission on the grating structural parameters is analysed in detail.     

基于光束的相干特性拓展双缝实验教学实验内容

对部分相干光束的双缝实验干涉条纹进行了研究。利用转动的毛玻璃以及两个透镜构成了一个简单的产生部分相干光束的光学系统,通过调整毛玻璃与两个透镜的共焦点之间的距离,可以定量地控制光束的相干性。对不同相干性的光束经过双缝干涉之后的光强进行了实验观测,发现光束的相干性会对双缝干涉条纹的衬比度产生影响,光束的相干性越低,条纹衬比度也越小。并对实验结果进行了理论模拟,理论数值模拟的结果与实验观测结果基本一致。     

Diffraction loss analysis of a plane-parallel optical cavity with a phase step and a slit aperture

A model for calculating the round trip diffraction loss in a plane-mirror cavity with an intracavity phase step and an infinite slit aperture is developed. The round trip remaining intensity fraction for the low order transverse cavity modes can be calculated for any given location of the slit aperture and the phase step along the cavity and for any given phase delay on the phase step. The diffraction loss on the slit aperture is found to be a periodic function of the phase delay on the phase step. Transformation of the lasing spectrum emitted from a broadband pulsed dye laser on moving the phase step along the oscillator cavity is reproduced theoretically. The lasing spectrum affected by the phase step is interpreted as the wavelength dependence of the remaining intensity fraction for the principal transverse mode.     

Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis

In this paper, the scattering/transmission inside a step-modulated subwavelength metal slit is investigated in detail. We firstly investigate the scattering in a junction structure by two types of structural changes. The variation of transmission and reflection coefficients depending on structural parameters are analysed. Then a multi-mode multi-reflection model based on ray theory is proposed to illustrate the transmission in the step-modulated slit explicitly. The key parts of this model are the multi-mode excitation and the superposition procedure of the scatterings from all possible modes, which represent the interference and energy transfer occurring at the interfaces. The method we use is an improved modal expansion method (MEM), which is a more practical and efficient version compared with the previous one [C. Li, Y.S. Zhou, H.Y. Wang, F.H. Wang, Opt. Express 19, 10073 (2011)]. In addition, some commonly used methods including FDTD, scattering matrix method and improved characteristic impedance method are compared with MEM to highlight the accuracy of these methods.     

Fraunhofer diffraction of light with orbital angular momentum by a slit

We study the Fraunhofer diffraction problem while taking into account the orbital angular momentum of light. In this case, the phase singularity of the light beam is incident on the slit in two different cases: in one, it is incident slightly above the slit, and in the other it is centered on the slit. We observed that the symmetry and the fringe formation in the interference pattern strongly depend on the amount of orbital angular momentum and the slit position in relation to the beam.     

Optical resonance in a narrow slit in a thick metallic screen.

Interaction of TM-polarized waves with a subwavelength thick metallic slit has been analyzed. A Fabry-Pérot-like behavior is reported. The resonance peaks, however, have very low magnitude and a systematic shift towards longer wavelengths is observed. The slit being narrow, this shift can be interpreted as the result of an aperture effect. Spectral transmission from a periodic array of such slits features the same peaks with a high increase in their magnitude, confirming that a grating acts as an amplifier of those resonances. Such a mechanism might explain the enhancement of the transmission observed in recent experiments [T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature (London) 391, 667 (1998)].     

Point source diffraction by a slit in a moving fluid

The diffraction of a spherical acoustic wave generated by a point source from impedance slit in a moving fluid is investigated. The diffracted wave is calculated in the far field regime as a sum of fields produced by the edges of the slit and an incident field. The Myers’ impedance conditions are assumed along the edges of the slit. Such conditions are well adopted for the boundaries of the impedance barriers and yield reliable predictions of the diffraction patterns. A Wiener–Hopf technique is invoked to resolve the problem in combination with Fourier transform techniques and asymptotic analysis. The appositeness of the results and the effect of pertinent physical parameters on the separated field are presented and analyzed graphically.     

Tunable plasmon resonance wavelength of the periodic gold film with converging and diverging shaped slits and grooves

We investigate a periodic slit-groove metal array with converging and diverging shaped channels by using the finite-difference time-domain (FDTD) method. We show that the peaks and dips of the transmission spectra can be tuned by the geometry parameters of the groove. And the resonance modes are strongly correlated with the groove depth and width of both ends of the groove, and the transmission dip between the resonance modes can be modulated by these parameters. However, the distance between the slit and the groove has little influence on the transmission. We show that the periodic slit-groove with diverging and converging shaped channels is useful for the design of plasmonic devices.     

Confinement of infrared radiation to nanometer scales through metallic slit arrays

One-dimensional metallic slit array has been intensively studied in the spectral range from ultraviolet to near-infrared due to its enhanced transmission for transverse magnetic waves. However, the transmission enhancement is sensitive to the wavelength of incident radiation because of resonance characteristics. In this paper, we theoretically demonstrate that confining mid-infrared radiation to nanometer scales with a large transmission enhancement can be achieved from an aluminum slit array in a wavelength-insensitive manner, for potential applications in localized heating and nanothermal patterning. The Poynting vector and energy density calculated from the rigorous coupled-wave analysis (RCWA) are used to explain the strong localization of electromagnetic energy in the near-field regime. Furthermore, the localization of energy is also studied when a dielectric substrate is used to support the slit array in practical applications.     

杨氏双缝干涉一种简便的波函数解释

利用波函数对杨氏双缝干涉条件进行了推导,与利用光的波动性推导结果一致。由于充分考虑了缝无限细的条件,推导过程和结果更加强调了光的干涉性,更加突显了杨氏双缝干涉的特点,物理图像更加清晰。     

Multiple paths to enhance optical transmission through a single subwavelength slit

In this Letter, we explore transmission properties of a single subwavelength slit flanked by a finite array of grooves made on a thick metallic film. We identify three main mechanisms that can enhance optical transmission: groove cavity mode excitation (controlled by the depth of the grooves), in-phase groove reemission (controlled by the period of the groove array), and slit waveguide mode (controlled by the thickness of the metal film). By tuning these geometrical parameters, enhancements of transmission of light by up to 2 orders of magnitude can be achieved when all three mechanisms coincide. Experimental verification of these findings is also shown for structured silver films fabricated by focused-ion-beam milling.