Small Divergence Angle Research Articles

A 3D particle model for the plume CEX simulation

ABSTRACTCharge Exchange (CEX) ion is the main factor causing the plume pollution. The distribution of CEX ions is determined by the distribution of beam ions and neutral atoms. Hence, the primary problem in the study of the plume is how to accurately simulate the distribution of beam ions and neutral atoms. At present, the most commonly used model utilised for the plume simulation is the analytical model proposed by Roy for the plume simulation of the NASA Solar Technology Application Readiness (NSTAR) ion thruster. However, this analytical model can only be applied to the ion beam with small divergence angles. In addition, the analytical model is no longer applicable to the simulation for the plume of a new type of ion thruster that appeared recently, which is called the annular ion thruster. In this paper, a 3D particle model is proposed for the plume simulation of ion thrusters consisting of the particle model for beam ions, the Direct Simulation Monte Carlo (DSMC) model for neutral atoms and the Immersed Finite Element-Particle In Cell-Monte Carlo Collision (IFE-PIC-MCC) model for CEX ions. Then, the plume of the NSTAR ion thruster is simulated by both Roy's model and the 3D particle model. The simulation results of both models are then compared with the experimental results. It is shown that the numerical results of the 3D particle model agree well with those of the analytical model and the experimental data. And this 3D particle model can also be used for other electric thrusters.

Enhanced random laser by metal surface-plasmon channel waveguide

Compared with conventional lasers, the random laser is realized through strong multiple scatterings in disordered gain system. In this paper, random lasing (RL) in one-dimensional metal surface plasmon (SP) waveguide with gold-plated self-formed silicon pyramids was investigated comprehensively. Consequently, the emission intensity of RL was enhanced dramatically and the RL threshold was reduced significantly through Au-coated Si spiky tips. Meanwhile, one-dimensional metal SP channel waveguides confined the emitting light in a certain direction with a small divergence angle. Using FDTD simulations, it was found that the enhancement effect for RL is likely attributed to the localized surface plasmon (LSP) field. In addition, the LSP field nearby the spiky tips can enhance field-molecule interaction, which was benefit for lasing in small scale. The results in this letter supplied a feasible method to realize the application of RL in subwavelength optical elements.

Compact high-efficiency vortex beam emitter based on a silicon photonics micro-ring.

Photonic integrated devices that emit vortex beam carrying orbital angular momentum are becoming key components for multiple applications. Here we propose and demonstrate a high-efficiency vortex beam emitter based on a silicon micro-ring resonator integrated with a metal mirror. Such a compact emitter is capable of generating vortex beams with a high efficiency and small divergence angle. Vector vortex beams of various topological charges are selectively generated by the emitter at different wavelengths with an emission efficiency of up to 37%.

Giant enhancement of emission efficiency and light directivity by using hyperbolic metacavity on deep-ultraviolet AlGaN emitter

Despite the demands of growth, the development of deep-ultraviolet (UV) light-emitting diodes (LEDs) still suffers from the fundamental limits of material defects and the anisotropic optical property of AlGaN multiple quantum-wells (MQWs), resulting in an extremely low emission output. Here, we present a novel approach to address this issue by using a nanoscale hyperbolic metacavity on the deep-UV LED, where the resonant modes of metacavity are excited. An intense plasmon field is consequently feedback to the MQW. This strong resonant mode feedback allows the dipoles of MQW recombine directionally, thereby achieving enhancements of radiative emission rate by a factor of 160 and quantum efficiency by a factor of 3.5. It also shows the capability of metacavity in tailoring the direction of light emission, leading to a 520% increase in total emission intensity and 148% increase in emission extraction. A small divergence angle of 65° of LEDs is therefore demonstrated. Our study clearly shows that the use of metacavity is a promising candidate for the highly-desired efficiency and directivity deep-UV applications, and the metacavity effect can be extended to other nanoscale devices, such as nanolaser, single photon source, nano-biosensor, and nano-antenna.

Characteristics of a high-power ion beam deflection system necessary to deflect the hypothetical asteroid 2017 PDC

The July 2027 impact date for the hypothetical asteroid 2017 PDC, that is the subject of an emergency response exercise, leaves just over ten years to implement a deflection approach. The analyses herein allocate four years to the design, fabrication, assembly, test and launch of a notional high-power Ion Beam Deflection (IBD) vehicle to meet a launch readiness date no later than May 2021. Using this launch date along with estimates for the vehicle mass and performance characteristics of the electric propulsion system, low-thrust trajectory analyses indicate a 2.56-year flight time to rendezvous with 2017 PDC. This would leave 3.6 years to execute the actual deflection phase. A 160-kW IBD vehicle could deflect 2017 PDC by at least one Earth radius within this time provided the asteroid's actual diameter was less than about 140 m and its density was 2 g/cm3 or less. Larger diameters and/or higher densities would require a higher power IBD vehicle, multiple IBD vehicles, or a longer deflection phase. Ion beam deflection is largely independent of the characteristics of the threat object, but its effectiveness, like all deflection approaches, is sensitive to both the asteroid mass and the time available for deflection. The characteristics of IBD, i.e., large standoff distance between the spacecraft and the asteroid surface, as well as ion beam divergence angles of a few degrees, facilitate the possible simultaneous use of multiple IBD vehicles to improve the performance and robustness of the asteroid deflection. The 65-cm diameter, 20-kW NEXIS ion thruster developed in support of the Jupiter Icy Moons Orbiter mission concept is particularly well suited for application to a high-power IBD system. It has demonstrated a small ion beam divergence angle and operation at 20 kW for over 2000 h. Completion of the development and flight qualification of this technology would significantly reduce the risk and time necessary to respond to the discovery of potentially hazardous asteroid in the size range of 50- to 140-m diameter.

Directional beaming of light from a subwavelength metal slit with phase-gradient metasurfaces

In this article, we demonstrate directional beaming of light from a metal nanoslit surrounded with phase-gradient metasurfaces on both sides. Distinct from the grating-based beaming structures, here the momentum mismatch between the surface wave and radiation wave is overcome by the phase-gradient metasurfaces. The deviation angle of the directional beam can be flexibly adjusted by appropriately arranging the phase-gradient of metasurfaces on each side of the nanoslit. The metasurface-based beaming structures also present the ability to operate with high diffraction efficiency and small divergence angle, implying various potential applications in nanophotonics.

The switching of strong spin wave beams in patterned garnet films

The application of spin waves in communication with information encoded in amplitude and phase could replace or enhance existing microelectronic and microwave devices with significantly decreased energy consumption. Spin waves (SW) are usually transported in a magnetic material shaped to act as a waveguide. However, the implementation of SW transport and switching in plane homogeneous magnetic films and running as a narrow beam with a small divergence angle still present a challenge. We propose a realization of a strong SW switchers based on a patterned yttrium iron garnet (YIG) film that could serve as a magnonic fundamental building block. Our concept relies on the creation of a narrow beam of relatively short-wavelength SW by effect of a total non-reflection, found to be tied to refraction on the decreasing internal magnetic field, near a line of antidots at YIG. Nonreciprocal SW excitation by a microstrip antenna is used for controlling the direction of the signal flow. We demonstrate unique features of the propagation of microwave-excited SW beams, provide insight into their physics and discuss their potential applications in high-frequency devices.

High-Power Single-Spatial-Mode GaSb Tapered Laser around 2.0 μm with Very Small Lateral Beam Divergence**Supported by the National Basic Research Program of China under Grant Nos 2014CB643903 and 2013CB932904, the National Natural Science Foundation of China under Grant Nos 61435012 and 61290303, and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences under Grant No XDB01010200.

We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles are fabricated to optimize the output power and spatial-mode performance. The best devices exhibit single-spatial-mode operation with room-temperature output power up to 350 mW in continuous-wave mode at an emission wavelength around 2.0 μm with a very small far-field lateral divergence angle, which is beyond state of the art in terms of single-spatial-mode output power.

High-directional vortex beam emitter based on Archimedean spiral adiabatic waveguides.

Integrated devices that emit light beams with orbital angular momentum (OAM) are becoming key components for wide-ranging applications. Here we propose and demonstrate a highly directional silicon photonic vortex beam emitter based on a 3-turn Archimedean spiral adiabatic waveguide integrated with an angular grating. Such a compact emitter is capable of generating vortex beams with small divergence angles and high directivity. Various orders of OAM modes can be selectively generated by the emitter at different wavelengths with a side-mode suppression ratio as large as 13.6 dB.

Design, fabrication and characterization of a hybrid metal-dielectric nanoantenna with a single nanocrystal for directional single photon emission

In this work we detail the fabrication method of a hybrid metal-dielectric nanoantenna with a single nanocrystal quantum dot positioned in its center. We have recently shown in [Nano Lett.16, 2527 (2016)] that this device efficiently directs photons from the nanocrystal emission into a small divergence angle perpendicular to the nanoantenna surface. The fabrication method presented here is robust and can be fine-tuned by only a few parameters to achieve high yield of such nanostructures.

Reduction of a beam diameter by decreasing the divergence angle of an incident beam in a compact ion microbeam system producing several-hundred-keV beam

A compact ion microbeam system, which comprises a three-stage acceleration lens and a duoplasmatron-type ion source and produces beam of several hundred kiloelectron-volts, has been developed to form a beam that has a diameter of several micrometers. Previous studies have indicated that a small divergence angle of an incident beam is required to improve the demagnification of the three-stage acceleration lens. A simulation of an ion beam extraction demonstrated that the optimum distance between the anode and the extraction electrode in the ion source could lead to an ion beam being generated with the smallest possible divergence angle. As a result, a hydrogen beam with a 2.6μm diameter was experimentally produced at 120keV.

Principles and simulation of spectropolarimetirc imaging technique based on static dual intensity-modulated Fourier transform

Traditional imaging spectropolarimetry generally requires slit, moving parts, electrically tunable devices, or the use of micropolarized arrays. Furthermore, the acquired raw data are a physical superposition of interferogram and image. Given their complicated structure, poor seismic capacity, low detection sensitivity, and heavy computations with approximation in spectral reconstruction, meeting the needs for applications in aviation, remote sensing, and field detection is difficult. To overcome these drawbacks, a new spectropolarimetric imaging technique based on static dual intensity-modulated Fourier transform is presented. The system consists of a front telescopic system, two phase retarders, a linear polarizer, a Wollaston prism, a Savart polariscope, a linear analyzer, a reimaging system, and a charge-coupled device (CCD) array detector. The incident light is modulated through a module of polarization spectrum modulation, which consists of the retarders and the polarizer. The Wollaston prism splits the modulated incident light into two equal intensities, orthogonally polarized components with a small divergent angle. After passing through the interference module, which is composed of the Savart polariscope and the analyzer, then the reimaging system, two full-polarization interferograms, which are the superposition of background images and interference fringes, are recorded simultaneously on a single CCD. The pure target image and the pure interference fringes can be simply achieved from the summation or the difference of the two interferograms. Spectral and complete polarization information can be acquired by using the Fourier transform of the pure interference fringes. The principle and the configuration of the system are described here in this paper. The reconstruction processes of the target image and the full Stokes polarization spectra are theoretically analyzed and mathematically simulated. The results show that the system can availably separate background image from interference fringes of the target, achieving high-precision spectral reconstruction and effective extraction of the complete polarization information. Compared with the features of existing instruments, one of the salient features of the described model is to use the dual-intensity modulation, which can avoid mutual interference between the image and the fringes from the hardware and is conducive to the extraction of pure interference fringes with high signal-tonoise ratio (SNR). With this feature, the inadequacies on traditional spectral reconstruction, such as large computation, heavy data processing, and low accuracy of acquired information, are overcome. Moreover, the entrance slit in the front telescopic system is removed, which greatly increases the transmittance and flux of the incident light and improves the SNR of the interferogram. The modified Savart polariscope is used in the interference module. Its transverse shearsplitting principle further enlarges the field of view and increases the spectral resolution of the straight fringes. Thus, this design has the advantages of good stability, high spectrum, high sensitivity, large SNR, high-precision information reconstruction, and low-complexity data processing, as well as simultaneous detection of image, spectrum, and complete polarization information. This work will provide an important theoretical basis and practical instruction for developing new spectropolarimetric imaging technique and its engineering applications.

LED Lens for Rectangular Beam with Small Divergence Angles

We have designed a new TIR(Total Internal Reflection) structure for generating an LED lens which can produce a rectangular beam with small divergence angle in two perpendicular directions for an optical guidance system. The lens can control the divergence angle in the horizontal direction to be a small value of about 8° with a 1 mm × 1 mm LED source, also in the vertical direction it can be about 7°, with optical collection efficiency higher than 0.83. After the lens is manufactured, the work demonstrates that the lens is suitable for an optical guidance system.

GaN-based vertical-cavity surface emitting lasers with sub-milliamp threshold and small divergence angle

A GaN-based vertical-cavity surface emitting laser (VCSEL) structure featuring a silicon-diffusion-defined current blocking layer for lateral confinement is described. Sub-milliamp threshold currents were achieved for both 3- and 5-μm-aperture VCSELs under continuous-wave operation at room temperature. The vertical cavity was defined by a top dielectric distributed Bragg reflector (DBR) and a bottom epitaxial DBR. The emission spectrum exhibited a single peak at 411.2 nm with a linewidth of 0.4 nm and a side mode suppression ratio of more than 10 dB before device packaging. The full-width-at-half-maximum divergence angle of the 3-μm-aperture VCSEL was as small as approximately 5° which is the lowest number reported. These results implied the 3-μm-aperture VCSEL was in near single-mode operation.

Angle extended linear MEMS scanning system for 3D laser vision sensor

Scanning system is often considered as the most important part for 3D laser vision sensor. In this paper, we propose a method for the optical system design of angle extended linear MEMS scanning system, which has features of huge scanning degree, small beam divergence angle and small spot size for 3D laser vision sensor. The principle of design and theoretical formulas are derived strictly. With the help of software ZEMAX, a linear scanning optical system based on MEMS has been designed. Results show that the designed system can extend scanning angle from ±8° to ±26.5° with a divergence angle small than 3.5mr, and the spot size is reduced for 4.545 times.

利用Doppler测速法实现小发散角锶原子速度分布的测量

利用Doppler测速法实现小发散角锶原子速度分布的测量

A Flat-Lensed Spiral Phase Plate Based on Phase-Shifting Surface for Generation of Millimeter-Wave OAM Beam

A multilayer phase-shifting-surface-based flat plate is designed to offer a combination of lens and spiral phase plate (SPP) for orbital angular momentum (OAM) beam generation and convergence at 60 GHz. The proposed design consists of a series of phase-shift unit cells to control the emergent phase and form a flat lens for the purpose of beam focusing. The results of simulation and experiment verify that the OAM beam with small divergence angle can be achieved.

Transmission type flat-panel X-ray source using ZnO nanowire field emitters

A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

Electron properties of a microcolumn with a CNT tip

We investigated a possibility of the CNT tips as an electron emitter tip of a miniaturized microcolumn. For the purpose, we analyzed potential distribution, field distribution and electron beam properties of the conventional tip, single-walled nanotube (SWNT) and double-walled nanotube (DWNT). From the result, we made certain that the nanotube emitters have advantages in small beam divergence angle and beam current enhancement. Especially, the SWNT has the largest field strength at the tip apex among the three tips, thus it can emit enough electron current even at a low extract bias voltage. On the other hand, the DWNT has the smallest electron beam divergence angle. It means that the tip has the largest depth of focus among the three investigated tips.

Top Grating, Surface-Emitting DFB Quantum Cascade Lasers in Continuous-Wave Operation

We demonstrate room temperature, continuous-wave operation of top grating based surface-emitting distributed feedback quantum cascade lasers at $\lambda \sim 4.8~\mu \text{m}$ . The second-order metal/semiconductor grating structure allows efficient surface emission for the transverse-magnetic-polarized light. The CW output power from the substrate facet reached 94 mW at 25 °C, with a low threshold current density of 1.21 kA/cm2. Single-mode emission with a side-mode suppression ratio about 30 dB is continuously tunable by the heat sink temperature or injection current. A far-field radiation pattern with a small divergence angle of $0.58 {^{\circ }} \times 16.2^{\circ }$ is obtained. Our work may contribute to the fabrication approach for substrate-emitting distributed feedback lasers based on a very simple processing.