Parameters Of Incident Beam Research Articles

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

The Propagation Properties of a Lorentz–Gauss Vortex Beam in a Gradient-Index Medium

Based on the Huygens–Fresnel integral and ABCD matrix, the propagation equation for the Lorentz–Gauss vortex beam (LGVB) in a gradient-index medium (GRIN) is rederived. The evolution of the intensity and phase distributions of an LGVB through a GRIN medium are numerically calculated as a function of the gradient-index parameter with changes in the incident beam parameters. The results showed that the propagation path and intensity distributions changed periodically with increasing propagation distance. In contrast, phase distributions change at multiples of π/β or 2π/β, depending on whether the M values are odd or even, respectively. At the same time, the parameters of the gradient index determine the periodic values of the Lorentz–Gauss vortex beams during propagation, and as β increased, the period of evolution decreased. The Lorentz–Gauss vortex beam propagating through the gradient index will develop from a square beam to a Gaussian vortex beam more quickly with an increase of w0x=w0y. In addition, the topological charge affects the size of the dark spot at the center of the beam and the size of the beam, causing the phase distributions to change periodically in the medium. This study is beneficial for laser optics and optical communications.

Optical trapping force on a stratified chiral particle by high-order Bessel beam.

We examined optical trapping force (TF) exerted on non-uniform chiral stratified spheres by a high-order Bessel beam (HOBB). Present theories were proven to be valid by comparison with the existing reference. Numerical simulations considering the effects of various parameters on TF are displayed in detail. The results show that different chirality distributions in stratified chiral sphere will affect significantly the trapping characteristics, and a stable three-dimensional capture can be realized only by selecting the appropriate parameters of incident beam and particles. The theoretical investigations may provide an analytical method to help understand the interaction of light with more complex stratified chiral cells and thus become an encouraging approach to better design an optical manipulation system.

Anisotropic and valley-resolved beam-splitter based on a tilted Dirac system

We investigate theoretically valley-resolved lateral shift of electrons traversing an n–p–n junction bulit on a typical tilted Dirac system (8-Pmmn borophene). A gauge-invariant formula on Goos–Hänchen (GH) shift of transmitted beams is derived, which holds for any anisotropic isoenergy surface. The tilt term brings valley dependence of relative position between the isoenergy surface in n region and that in the p region. Consequently, valley double refraction can occur at the n–p interface. The exiting positions of two valley-polarized beams depend on the incident angle and energy of incident beam and barrier parameters. Their spatial distance D can be enhanced to be ten to a hundred times larger than the barrier width. Due to tilting-induced high anisotropy of the isoenergy surface, D depends strongly on the barrier orientation. It is always zero when the junction is along the tilt direction of Dirac cones. Thus GH effect of transmitted beams in tilted Dirac systems can be utilized to design anisotropic and valley-resolved beam-splitter.

Behavior of the central intensity of generalized humbert-gaussian beams against the atmospheric turbulence

In this paper, we present a theoretical study of the propagation properties for Generalized Humbert-Gaussian beams (GHGBs) passing through a turbulent atmosphere. The axial intensity distribution of beams propagating through atmospheric turbulence is evaluated analytically based on the Huygens-Fresnel diffraction integral and the Rytov theory. The impact of the incident beam parameters and the turbulent strength on the output axial intensity is investigated through numerical illustrations. The results show that the propagation of GHGBs is faster when the atmosphere is very turbulent for small wavelength and small beam waist.

Thermally Reconfigurable Hologram Fabricated by Spatially Modulated Femtosecond Pulses on a Heat-Shrinkable Shape Memory Polymer for Holographic Multiplexing.

Optical security involving the use of light to achieve distinctive vision effects has become a widely used approach for anticounterfeiting. Holographic multiplexing has attracted considerable interest in multiplexing security due to its high degree of freedom for manipulating the optical parameters of incident laser beams. However, the complex and time-consuming fabrication process of metasurface-based holograms and the sophisticated nature of holographic imaging systems have hindered the practical application of holographic multiplexing in anticounterfeiting. Combining holography with shape memory polymers to construct reconfigurable holograms provides a simple and efficient way for holographic multiplexing. This paper proposes a reconfigurable four-level amplitude hologram fabricated on a heat-shrinkable shape memory polymer using spatially modulated femtosecond laser pulses. Simply by triggering the shape recovery of the polymer through heating, the amplitude modulation of light by the hologram is reconfigured through the shrinking of processed microcrater pixels with three diameters, which enables variation to be achieved in reconstructed holographic images. Examples of holographic multiplexing and data encryption are used to validate the proposed method. The proposed economic and simple approach for holographic multiplexing provides an integrated and single-material solution to packaging and optical security, which has extensive potential in anticounterfeiting and optical encryption.

Focusing properties and focal shift of a vortex cosine-hyperbolic Gaussian beam

In this paper, we investigate the focusing properties of a vortex-cosh-Gaussian (vChG) beam passing through a converging thin lens. Based on the Huygens–Fresnel diffraction integral, we derived the analytical propagation equation as well as the beam width expression of a focused vChGB. It is shown that the focusing properties including the focal shift of the focused vChGB are crucially dependent on the incident beam parameters namely the decentered parameter and the topological charge in addition to the Gaussian Fresnel number \(N_{F}\). From typical numerical examples, it is found that the focused vChGB is transformed into a multi-lobes structure shape at the real focus plane, and the principal maximum intensity of the beam is located away from the axis. The amount of focal shift, which is determined from the minimum spot size criterion, is strongly dependent on the Fresnel number, the decentered parameter and the vortex charge m. The obtained results may be useful for the applications of the vChGBs in beam shaping and beam focusing.

Open Z-scan analytical model for multiphoton absorption

We present an open-aperture elliptic Gaussian beam Z-scan theory for thin nonlinear optical material possesses simultaneous $$ \left( {N - n} \right) $$ nonlinear absorption processes with residual linear absorption. We show that an approximate analytical but closed-form expression for the normalized energy transmittance is possible by means of the weak nonlinearities approximation. The elaborate theory can be used to fit the open Z-scan traces allowing the determination of material’s nonlinear absorption coefficients and incident Gaussian beam parameters. The contribution of absorptions of distinct order can also be identified, separated and compared.

Photonic nanojet mediated Raman enhancement: Vertical Raman mapping and simple ray matrix analysis

AbstractA new method for enhancing the Raman scattering signal has emerged recently, based on dielectric enhancement. Especially promising is the dielectric method based on microspheres and photonic nanojet. In this paper, geometrical aspects and the influence of the incident beam parameters on Raman enhancement by silica microspheres were systematically investigated in three steps: by characterizing the incident beam using knife‐edge method, performing horizontal and vertical Raman mapping imaging, and analyzing the results using ray transfer matrix analysis. Maps show a distinct enhancement (hotspot) area caused by the microsphere photonic nanojet and lens effect compared to a plain silicon substrate. Enhancement value on maps was the highest (5.7×) for 0.50 numerical aperture objective, when the incident beam size matched the microsphere diameter, and the focus of the incident beam was below the top of the sphere, so that the output beam focus was at the microsphere–substrate contact area. This geometrical configuration was confirmed as ideal by performing simple ray transfer matrix analysis. The ideal ranges of incident and output beam parameters match with the measured hotspot area. This three‐step process and the usage of vertical Raman mapping have been, for the best of our knowledge, performed for the first time in such configuration. This research introduces a new way of investigating microsphere‐assisted Raman enhancement, offers different approach to microsphere optics research, and improves current knowledge of the influence of the incident beam on the enhancement.

Introduction of generalized Bessel–Laguerre–Gaussian beams and its central intensity travelling a turbulent atmosphere

The so-called Generalized Bessel–Laguerre–Gaussian (GBLG) beam is introduced, in this paper, and an approximate formula of the average axial intensity of its propagation through a turbulent atmosphere is investigated using the extended Huygens–Fresnel diffraction integral in the paraxial approximation and on the Rytov theory. The analytical expression elaborated is regarded as the main result of this work. Several above studies are derived here as special cases from our research. The impact of some parameters, including incident beam parameters and turbulence strength, on the distribution of the axial intensity of the GBLG beam and on the profiles of some particular beams through a turbulent atmosphere are carried out numerically in the paper. From our numerical results-, the propagation of Gaussian beams, Laguerre–Gaussian beams and Bessel–Gaussian beams through the considered medium are deduced as particular cases.

Abstract ID: 77 Monte Carlo simulation of the Elekta VersaHD linac with Elekta’s Stereotactic Conical Collimation System

Purpose Small field dosimetry remains a challenging task. The difficulties associated with small fields measurements become more pronounced for field sizes less than 1 cm. To overcome these difficulties it has been suggested to employ Monte Carlo (MC) techniques. The purpose of this work was to report the results of commissioning and MC validation of the new Elekta stereotactic conical collimator system for 6 MV flattening filter free (FFF) beams on Elekta VersaHD linac. Methods Commissioning measurements for stereotactic cones with diameters of 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm included relative output factor (ROF), percentage depth dose (PDD) and off-axis ratio (OAR) measurements and were performed with SRS diode. MC simulations were performed using EGSnrc. The incident electron beam parameters were adjusted to match the measured data (PDD and OAR) for set of MLC-based open fields. For each cone, aperture size was adjusted to match MC calculated and measured OAR profiles. Penumbra width (defined as 20%–80% distance) comparison of MLC-based and cone-based fields for a static angle case and for a full arc was performed. Angular distribution of photons collimated with MLC and with the cones was calculated. Leakage for the MLC and for the cones was determined. Results For MLC-based fields, agreement between calculated and measured values was within 1%/0.5 mm for PDDs, within 1%/1 mm for OARs, and within 3% for ROFs. For stereotactic cones, the agreement in PDD and OAR profiles was within 1%/0.5 mm and the ROFs agreed within 3%. The measured ROFs were 0.564, 0.645, 0.706, 0740 and 0.770 for the 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm cones, respectively. For one static MLC-based 1 × 1 cm field, penumbra was 5.6 mm in the in-plane direction and 8.4 mm in the cross-plane direction, compared to 4 mm in both directions for the 10 mm cone. The cone leakage was found to be 0.5% for both energies. Conclusions Results of our MC calculations were found to be in good agreement with the measurements thus confirming accuracy of our MC model for the Agility MLC.

Optimisation of the prism coupling of optical whispering-gallery-mode microcavities

The methods for increasing the coupling efficiency of a prism with spheroidal microcavities, aimed at exciting whispering-gallery modes, have been analytically investigated. Optimal angles of incidence and incident beam parameters are obtained for a spheroidal cavity. The cavity eigenfrequency shift caused by the presence of a prism and the introduced loss by it is calculated.

Experimental study on the propagation characteristics of ring Airy Gaussian vortex beams

The auto-focusing and auto-healing profiles of linearly polarized ring Airy Gaussian vortex (RAiGV) beams in linear media are investigated experimentally based on spatial light modulators and computer-generated holograms. It is found that the parameters of incident beams greatly affect the auto-focusing profiles of RAiGV. The focal length increases as the radius of the primary ring, scaling factor and waist radius increases, and the focal length decreases slightly as topological charges increase. The peak intensity at focal point increases with the increasing topological charges and waist radius, or with the decreasing scaling factor and the radius of the primary ring. The phase singularity of the RAiGV beams remains unchanged during propagation. The RAiGV beams also exhibit remarkable resilience against perturbations and tend to reconstruct its intensity sharp. Meanwhile, the abruptly auto-focusing property can be controlled by blocking few inner or outer rings of the RAiGV beams. These studies provide useful insight in the study of Airy vortex beam and its further applications.

Cathodoluminescence studies of defects in coated boron nitride

Optical emission properties of boron nitride (BN) substrates, BN with alumina (Al2O3) coating, and thermally-annealed alumina-coated boron nitride (an-BN/Al2O3) were investigated under electron irradiation using cathodoluminescence (CL) measurements. Tests were performed, temperatures ranging from ~100 K to ~300 K, with monoenergetic beams from 5 keV to 30 keV, and electron flux densities from 1 nA · cm−2 to 500 nA · cm−2. These experiments were conducted to identify the effects of coating and thermal annealing on the nature and occupation of defect states in different samples with BN substrates. Previous studies have shown that these treatments can limit the charging of BN substrates. Consequently, thorough investigations of electron trapping and recombination processes as a function of low temperature, dose and charging/discharge were performed in order to explain the differences of electrical behaviour and compare the CL spectra of the three different samples studied. Broad features associated with the BN and sharper features resulting from the annealed alumina coating were observed. Changes in the intensity, energy, and width of the features with sample treatments were observed. Different incident beam parameters were used to associate these features with specific types of defect states. The effects of charging, temperature- and dose-dependent conductivity, and thermal annealing and aging of the samples on the CL spectra were investigated. These were used to study defect creation and occupation and to understand the predominant physical mechanisms and main structural and chemical differences between these ceramic configurations.

Uniform irradiation of a direct drive target by optimizing the beam parameters

Laser driven fusion requires a high-degree uniformity in laser energy deposition in order to achieve the high-density compression required for sustaining a thermonuclear burn. Nowadays, uniform irradiation of capsule is still a key issue in direct drive inertial confinement fusion. The direct drive approach is to drive the target with laser light, by irradiating it with a large number of overlapping laser beams. In the direct drive scheme, the laser deposition pattern on the target can be decomposed into a series of Legendre spherical harmonic modes. The high mode (shorter wavelength) nonuniformity can lead to Rayleigh-Taylor instability, which may result in the failure of target compression. This nonuniformity can be suppressed by thermal conduction and beam conditioning technologies, such as continuous phase plate, smoothing by spectral dispersion and polarization smoothing. The low mode (longer wavelength) nonuniformity is related to the number, orientation and power balance of laser beams, which is hard to suppress by thermal conduction and beam conditioning technologies. Generally, the nonuniformity of laser irradiation on a directly driven target should be less than 1% (root mean square, RMS), to meet the requirement for symmetric compression. Several methods have been proposed to optimize the irradiation configuration in direct drive laser fusion, such as truncated icosahedron with beams at the 20 faces and 12 vertices of an icosaherdron, dodecahedron-based irradiation configurations, self-organizing electrodynamic method, etc. However, limited by the different parameters of incident beams, the irradiation uniformity is often not satisfactory. Therefore, it is necessary to find new way to improve the irradiation uniformity and make it more robust. According to the analytical result, the irradiation nonuniformity can be decomposed into the single beam factor and the geometric factor. Simulation results show that the single beam factor is mainly determined by the parameters of the incident beams, including beam pattern, beam width and beam wavelength. By analyzing and simulating the single beam factor with different incident beam parameters, and comparing the single beam factor with the geometric factor, a matching relationship between them is found by using the optimized parameters. Based on the simulation results, a method to optimize the incident beam parameters is proposed, which is applied to the 32-beam and 48-beam irradiation configurations. The results show that there is a set of optimal incident beam parameters which can attain the highest irradiation uniformity for a given configuration. The feasibility to achieve more uniform irradiation by optimizing the incident beam parameters is proved. When the single beam factor is optimized in a directly driven inertial confinement fusion system, the restrictions on the beam pointing error and power imbalance between incident beams can be relaxed. The results provide an effective method of designing and optimizing the uniform irradiation system of direct drive laser facility.

Focal-plane field when lighting double-ring phase elements

The focal-plane field amplitude is calculated when lighting double-ring phase elements by flat and Gaussian beams. Emerging conditions in the minimum or maximum centers, including flat-top maxima, are given. For the field amplitude, we obtain equations that define the radius of the first zero-intensity ring based on the deduced expressions. The root values are listed for several parameters of optical elements and incident beams due to the lack of analytical solutions. Numerical simulation results are given for flat incident beams; they are fully consistent with the theoretical calculations.

The conversion of a Li’s flat-topped-Gaussian beam to a superposition of Kummer dark hollow beam by the illumination of a fractional radial Hilbert transform system

A new method of the generation of superposition of Kummer beam is introduced by the illumination of a fractional radial Hilbert transform (FRHT) system with an apertured spiral phase plate (SPP) instrument by a Li’s flattened Gaussian (LFTG) beam. To study the propagation properties of the produced beam, two main approximate analytical expressions are developed. The first one concerns the SPP integer topological charges and the second one is about the non-integer ones. From the both principle formulas devoted, some studies about the generation of the Kummer beam, with integer and non-integer topological charges, by the conversion of a fundamental Gaussian beam and the propagation of the LFTG beams through a FRHT system without apertured SPP are deduced in this work as special investigations of the main studies. For reason to determine the effects of the incident beam parameters and the optical system coefficients on the propagation characteristics of the created beam, several numerical calculations are carried out, analyzed and discussed in the work. Simples concluding remarks are outlined in the end of the paper.

Effect of turbulent atmosphere on the on-axis average intensity of Pearcey–Gaussian beam

The propagation characteristics of the Pearcey–Gaussian (PG) beam in turbulent atmosphere are investigated in this paper. The Pearcey beam is a new kind of paraxial beam, based on the Pearcey function of catastrophe theory, which describes diffraction about a cusp caustic. By using the extended Huygens–Fresnel integral formula in the paraxial approximation and the Rytov theory, an analytical expression of axial intensity for the considered beam family is derived. Some numerical results for PG beam propagating in atmospheric turbulence are given by studying the influences of some factors, including incident beam parameters and turbulence strengths.

The ablation mass of metals by intense pulsed ion beam irradiation

Ablation effect plays an important role in the process of material modification by intense pulsed ion beam (IPIB). As a direct observable in the process of target irradiated by IPIB, the ablation mass is a crucial physical quantity for understanding the interaction between IPIB and target material. Moreover, it is critical to uncover the mechanism of ablation by IPIB. In the present work, we used IPIB provided by BIPPAB-450 accelerator at Beihang University to bombard Zn, Pb, Sn, Cu, and W targets. By measuring the ablation masses under different energy densities, the ablation thresholds of Zn and Pb have been obtained. In addition, correlations between experimental data and incident beam parameters have been investigated. The results are helpful to understand the influence of beam parameter and material properties on the ablation mass.

Efficient end-fire coupling of surface plasmons in a metal waveguide

We present a semi-analytical study exploring the end-fire coupling of an incident beam into a surface plasmon mode propagating on a metal–dielectric interface. An energy-conserving projection method is used to solve for the resultant reflected and transmitted fields for a given incident beam, thereby determining the efficiency of the surface plasmon coupling. The coupling efficiency is found to be periodic with waveguide width due to the presence of a coupled, transversely propagating surface plasmon. Optimization of the incident beam parameters, such as beam width, position, and wavelength, leads to numerically observed maximum efficiencies of approximately 80% when the beam width roughly matches the width of the surface plasmon.