Annular Slits Research Articles

Particle Trapping Properties of Metal Annular Slits under Vector Field Excitation

This article presents the particle capture performance of annular slits, which offer a simple alternative to complex micro/nano structures used to excite and focus surface plasmon polaritons (SPPs). Additionally, the annular slits are compatible with a variety of vector light fields, generating diverse SPP field distributions under their excitation. These SPP fields can be regulated by varying the vector light field parameters, thereby offering the annular slit structure the ability to flexibly capture and manipulate particles. The rotation and movement of captured objects can be achieved by changing the position and phase difference of the incident beams with linear polarization. Different material and sized metallic particles can be stably captured with a radially polarized beam excitation due to the strong convergence. These capabilities are demonstrated by evaluating the optical force and trapping potential based on the finite difference time domain (FDTD) simulation. This study provides valuable insights into the practical application of annular slits for particle capture and manipulation.

Study on the Atomization Ability of the Annular Slit Nozzle Assembly with the Delivery Tube of Lower-limiting Flow

Study on the Atomization Ability of the Annular Slit Nozzle Assembly with the Delivery Tube of Lower-limiting Flow

High-throughput nuclear resonance time domain interferometry using annular slits.

Nuclear resonance time domain interferometry (NR-TDI) is used to study the slow dynamics of liquids (that do not require Mössbauer isotopes) at atomic and molecular length scales. Here the TDI method of using a stationary two-line magnetized 57Fe foil as a source and a stationary single-line stainless steel foil analyzer is employed. The new technique of adding an annular slit in front of a single silicon avalanche photodiode detector enables a wide range of momentum transfers (1 to 100 nm-1 by varying the distance between the annular slits and sample) with a high count rate of up to 160 Hz with a Δq resolution of ±1.7 nm-1 at q = 14 nm-1. The sensitivity of this method in determining relaxation times is quantified and discussed. The Kohlrausch-Williams-Watts (KWW) model was used to extract relaxation times for glycerol. These relaxation times give insight into the dynamics of the electron density fluctuations of glycerol as a function of temperature and momentum transfers.

Controllable axial optical chain beams using a holographic method.

Axial optical chain (optical bottle beams) beams are widely used in optical micromanipulation, atom trapping, guiding and binding of microparticles and biological cells, etc. However, the generation of axial optical chain beams are not very flexible at present, and its important characteristics such as periodicity and phase shift cannot be easily regulated. Here, we propose a holographic method to achieve the axial optical chain beams with controllable periodicity and phase. A double annular phase diagram is generated based on the gratings and lenses algorithms. The beam incident to the double annular slits was tilted from the optical axis to produce concentric double annular beams. The annular beam with different radius will produce the zero-order Bessel beam with different axial wave vector. Axial optical chain beams is produced by interference of two zero-order Bessel beams with different axial wave vectors. The phase and periodicity of the axial optical chain beams can be changed by changing the initial phase difference and radius of the double annular slits of the double annular phase diagram, respectively. The feasibility and effectiveness of the proposed method are demonstrated by theoretical numerical analysis and experiments. This method will further expand the application of axial optical chain beams in optical tweezers, optical modulation and other fields.

Zeroth- and first-order long range non-diffracting Gauss\u2013Bessel beams generated by annihilating multiple-charged optical vortices

We demonstrate an alternative approach for generating zeroth- and first-order long range non-diffracting Gauss–Bessel beams (GBBs). Starting from a Gaussian beam, the key point is the creation of a bright ring-shaped beam with a large radius-to-width ratio, which is subsequently Fourier-transformed by a thin lens. The phase profile required for creating zeroth-order GBBs is flat and helical for first-order GBBs with unit topological charge (TC). Both the ring-shaped beam and the required phase profile can be realized by creating highly charged optical vortices by a spatial light modulator and annihilating them by using a second modulator of the same type. The generated long-range GBBs are proven to have negligible transverse evolution up to 2 m and can be regarded as non-diffracting. The influences of the charge state of the TCs, the propagation distance behind the focusing lens, and the GBB profiles on the relative intensities of the peak/rings are discussed. The method is much more efficient as compared to this using annular slits in the back focal plane of lenses. Moreover, at large propagation distances the quality of the generated GBBs significantly surpasses this of GBBs created by low angle axicons. The developed analytical model reproduces the experimental data. The presented method is flexible, easily realizable by using a spatial light modulator, does not require any special optical elements and, thus, is accessible in many laboratories.

Numerical simulation of radial-stratified rotating detonation flow field structures with different injection patterns

Rotating detonation engine has been widely studied in recent years because of its high theoretical efficiency and heat release rate. In many numerical simulations, the combustible mixture is injected and fully filled at the head of the combustor. In this paper, annular injection slits are proposed and three representative injection patterns are simulated by changing the injection directions. Stable single-wave modes are formed in all three patterns and two kinds of combustible mixture layer structures are found, namely “L-shape” and “T-shape” structures. Following the combustible mixture layer, the detonation wave is not fully filled in the radial direction, thus radial and circumferential shock waves are induced from the detonation wave, forming more complex wave structures. After the radial shock wave, velocity vortex and significant deflagration are found and propagate with the shock wave, thus maintaining a higher pressure and temperature there.

Sub-wavelength annular-slit-assisted superoscillatory lens for longitudinally-polarized super-resolution focusing

A binary metallic superoscillatory lens assisted with annular subwavelength slits is proposed, which generates a longitudinally-polarized super-resolution focal point. The annular slits are designed to selectively transmit radially-polarized light. Simulations using the finite element method show a 0.24 λ focal spot with 21.8 dB of polarization purity and only 0.342 dB reduction in efficiency compared to a standard superoscillatory lens.

Numerical and experimental study of a novel aerodynamic foam breaker for foam drilling fluid

AbstractDefoaming is a key technology for increasing the efficiency of foam drilling in petroleum engineering. To enhance the performance of a mechanical foam breaker in foam drilling, a novel aerodynamic foam breaker with two annular slits was investigated in this study. The computational fluid dynamics code of ANSYS Fluent was used to simulate the velocity and pressure distribution inside the foam breaker, and the optimum distance between the two annular slits was determined based on the simulation methods. Meanwhile, a series of experiments were conducted to test the actual performance of the foam breaker. The results demonstrate that various factors may affect the efficiency of the foam breaker, including the foam gas‐liquid ratio, basic liquid viscosity, and air supply method. A higher gas‐liquid ratio of the foam and air supply pressure result in a superior foam breaker performance. The viscosity of the foam liquid phase exhibits exactly the opposite behavior, meaning that the foam breaker more effectively destroys foam from a lower‐viscosity liquid. This study verifies the practicability of this novel aerodynamic foam breaker and discusses the effects of different parameters on the defoaming percentage, and this study can act as a reference and guidance for subsequent defoaming research.

Enhanced near field focus steering of rectangular nanoslit metasurface structure

<sec> Surface plasmon polaritons (SPPs) are electromagnetic excitations propagating along the metal-dielectric interface. The SPPs excited by the metal micro/nano structures have the ability to manipulate the light on a subwavelength scale. The SPPs are of interest to researchers for its excellent subwavelength field confinement and local field enhancement. So far, the SPPs have found numerous applications in optical tweezers, biological sensors, and near-field holographic imaging, due to its subwavelength focusing. </sec><sec> In order to achieve enhanced near field subwavelength focusing, we propose a metasurface structure in this paper, which is composed of rectangular nanoslit circular arrays and multilayer annular slits. The function of the inner ring arrays is to excite SPPs and the outer ring slits is to enhance focusing. The electric field expression of SPP is studied analytically and theoretically, and then the principle of rectangular nanoslit to excite SPP and the inner ring array structure to generate central focusing are explained. The parameters of the structure are optimized, and the focusing characteristics of the metasurface structure under different polarization light are studied by using the finite difference time domain method. Furthermore, we explain the principle of the external structure enhancing focusing by introducing the theory of Fresnel zone plate and depth modulation. The analytical expressions and simulations show that when the incident polarized light has a wavelength of 980 nm, the focal spot having a full width at half maximum of about 650 nm, and the distribution of the coupled field can be approximately expressed by the first kind Bessel function. Compared with the former single circular array structure, the composite structure proposed in this paper has a good effect of both enhancing the central focusing and inhibiting the outer field divergence, and the center focal spot intensity is doubled. In addition, the electric field excited by the arbitrary linearly polarized light is also discussed, the electric field satisfies the form of the polarization angle sinusoidal function multiplied by a Bessel function. <sec> The research results of our study have some applications in subwavelength light modulation, near-field imaging, optical tweezers, and subwavelength scale optical information processing and so on. </sec></sec>

Compact acoustic lens composed of annular cavities covered by a membrane

A thin planar acoustic lens composed of concentric annular slits on a circular steel plate covered by a membrane made up of aluminum foil is numerically designed, and its performance in focusing low-frequency sound in air is experimentally demonstrated. Resonant fundamental modes of the membrane-backed cavities are calculated via the Finite-Element Method. By carefully adjusting the radii of the concentric cavities, the phase discontinuity across the cavities can be employed to achieve constructive interference of sound waves at a focal length of 200 mm, which is close to the acoustic wavelength, at 2190 Hz. The designed lens has an overall radius which is approximately one fourth of the radius of a conventional acoustic Fresnel lens employing a wavelength path length difference between adjacent cavities.

Metallic Fresnel zone plate implemented on an optical fiber facet for super-variable focusing of light.

We propose and investigate a metallic Fresnel zone plate (FZP/MFZP) implemented on a silver-coated optical fiber facet for super-variable focusing of light, the focal point of which can be drastically relocated by varying the wavelength of the incident light. We numerically show that when its nominal focal length is set to 20 μm at 550 nm, its effective focal length can be tuned by ~13.7 μm for 300-nm change in the visible wavelength range. This tuning sensitivity is over 20 times higher than that of a conventional silica-based spherical lens. Even with such high tuning sensitivity with respect to the incident wavelength change, the effective beam radius at the focal point is preserved nearly unchanged, irrespective of the incident wavelength. Then, we fabricate the proposed device, exploiting electron- and focused-ion-beam processes, and experimentally verify its super-variable focusing functionality at typical red, green, and blue wavelengths in the visible wavelength range, which is in good agreement with the numerical prediction. Moreover, we propose a novel MFZP structure that primarily exploits the surface-plasmon-polariton-mediated, extra-ordinary transmission effect. For this we make all the openings of an MFZP, which are determined by the fundamental FZP design formula, be partitioned by multi-rings of all-sub-wavelength annular slits, so that the transmission of azimuthally polarized light is inherently prohibited, thereby leading to super-variable and selective focusing of radially polarized light. We design and fabricate a proof-of-principle structure implemented on a gold-coated fused-silica substrate, and verify its novel characteristics both numerically and experimentally, which are mutually in good agreement. We stress that both the MFZP structures proposed here will be very useful for micro-machining, optical trapping, and biomedical sensing, in particular, which invariably seek compact, high-precision, and flexible focusing schemes.

Generation of Electron Bessel Beams with Nondiffractive Spreading by a Nanofabricated Annular Slit

The shaping of a wavefront of free electrons has been experimentally realized very recently. We report the generation of an electron Bessel beam using a nanofabricated annular slit. We directly observe that electron Bessel beams propagate while maintaining a narrow beam width over a long propagation distance. In addition, we experimentally verify the self-healing property of these electron beams, which can reconstruct their shape after passing an obstacle. The experimental results are compared with simulation results of the propagation including a hexagonal slit. The present technique of electron Bessel beam generation can be used to develop a novel electron-beam-shaping, an atomic manipulation technique, and a new electron microscopy.

Dynamically Tunable Plasmonic Lens between the Near and Far Fields Based on Composite Nanorings Illuminated with Radially Polarized Light

We present a plasmonic lens with a dynamically tunable focal length in the mid-infrared region that is composed of gold film with annular slits and embedded vanadium dioxide (VO2) nanorings. When illuminated with radially polarized light, a perfect circularly symmetric focusing spot can be dynamically tuned between the near and far fields by decreasing temperature, and it can always be focused beyond the diffraction limit. A physical model of the tunable plasmonic lens is also proposed to explain the mechanisms by which the focal length is dynamically tuned. The field enhancement and the focal length can be further tuned by adding concentric annular slits and VO2 nanorings, respectively, while keeping the focusing spot size small. This provides a further step in the development of a perfect tunable plasmonic lens.

An Integrated Multistage Nanofocusing System

We demonstrate an integrated multistage nanofocusing system which combines a conventional objective, a surface plasmonic lens, and a center-positioned rounded-tip cone nanoparticle. The surface plasmonic lens, fabricated on the cover glass which has been mounted on the biological microscopic objective, is composed of several concentric annular slits for exciting propagating surface plasmonic wave. The rounded-tip cone nanoparticle is for further generating non-propagating localized surface plasmonic wave. It is revealed that the enhancement of the nanoscale optical field can be improved by carefully choosing the appropriate numerical aperture of the objective to match the specific nanostructure of the surface plasmonic lens and choosing the relatively big cone angle of the nanoparticle. The investigation shows that a highly confined electric field as small as 20 nm and an enhancement factor of 5 orders of magnitude can be achieved through this multistage nanofocusing system when the system is illuminated with a uniform radially polarized beam.

Far-field superfocusing with an optical fiber based surface plasmonic lens made of nanoscale concentric annular slits

We present experimental demonstration of light superfocusing by using an optical fiber based surface plasmonic (SP) lens with nanoscale concentric annular slits. A far-field, sub-diffraction-limit sized focus was achieved with an optical fiber based device. The performance of SP lenses with three and four annular slits was experimentally characterized. Guidelines and suggestions on designing the SP lens are provided. As a microscale device with nanoscale features, the fiber-based SP lens can provide a solution to bridging nanophotonics and conventional optics.

Analysis of a new annular multi-slits antenna using wave concept iterative process in cylindrical coordinates

In this paper, a new antenna for satellite applications is proposed. This antenna is designed to operate at any frequency desired. It consists of a circular microstrip patch antenna which incorporates concentric annular slits, and it is printed on a grounded substrate. The details of the proposed antenna design and numerical results are presented and discussed. The wave concept iterative procedure in cylindrical coordinates is used to analyze this new antenna. Using the proposed procedure, less computing time and memory are needed to calculate the electromagnetic parameters of the annular multi-slits antenna.

A Study on the flow Characteristics of the Spiral Flow Nozzle with the Width Change of Annular Slit[Author's correction

A Study on the flow Characteristics of the Spiral Flow Nozzle with the Width Change of Annular Slit[Author's correction

A Method to Estimate the Accuracy of Radial Flow—Based Permeability Measuring Devices

Radial flow experiment is often used to measure the permeability of fibrous porous media by the composites processing community. However, very little work has been done to calibrate the radial flow set-up with media of known permeability. This article presents a new method for calibrating the permeability measuring set-ups based on radial flows. A reference medium in the form of two concentric annular slits is created for the radial flow mold whose permeability is estimated analytically and numerically. It is observed that the experimentally measured permeability deviates from the theoretical and numerical permeabilities with an increase in the flow rate for an injection setup using a gear pump as well as a piston-cylinder pump. The deviation can be attributed to two possible reasons: one is the leakage between the calibration device and mold plate surfaces because of a slight mold deformation at higher flow rates, the other one is the increase in the gap clearance of the reference medium because of the higher gap pressures at higher flow rates. No such deviation is observed while measuring the permeability of a fiber mat at different flow rates. Hence, the proposed reference medium can calibrate a conventional radial flow-based permeability measuring setups at low flow rates; the accuracy thus obtained can be extended to higher flow rates as well if permeability of a fiber mat can be shown to remain constant with the flow rate.

A Study on the Flow Characteristics of the Spiral Flow Nozzle with the Width Change of Annular Slit

In comparison with previous researches fur swirling flow, the spiral flow self-generated in the spiral flow nozzle has some different characteristics. It is not needed a compulsive tangential momentum to get its velocity component and has long potential core, relatively low swirl ratio, and high focusing ability. In this study, the self-generated mechanism of the spiral flow was clarified and the effect on the width of annular slit on spiral flow characteristics was investigated experimentally and numerically. As a result, the existence of tangential velocity component regardless of a compulsive angular momentum is clarified and the results obtained by experiment have a satisfactory agreement with those by numerical method, quantitatively and qualitatively.

A Method to Estimate the Accuracy of Radial Flow-Based Permeability Measuring Devices

Radial flow experiment is often used to measure the permeability of fibrous porous media by the composites processing community. However, very little work has been done to calibrate the radial flow set-up with media of known permeability. This article presents a new method for calibrating the permeability measuring set-ups based on radial flows. A reference medium in the form of two concentric annular slits is created for the radial flow mold whose permeability is estimated analytically and numerically. It is observed that the experimentally measured permeability deviates from the theoretical and numerical permeabilities with an increase in the flow rate for an injection setup using a gear pump as well as a piston-cylinder pump. The deviation can be attributed to two possible reasons: one is the leakage between the calibration device and mold plate surfaces because of a slight mold deformation at higher flow rates, the other one is the increase in the gap clearance of the reference medium because of the higher gap pressures at higher flow rates. No such deviation is observed while measuring the permeability of a fiber mat at different flow rates. Hence, the proposed reference medium can calibrate a conventional radial flow-based permeability measuring setups at low flow rates; the accuracy thus obtained can be extended to higher flow rates as well if permeability of a fiber mat can be shown to remain constant with the flow rate.