Influence Of Beam Parameters Research Articles

Interaction of Hermite–Gaussian Beams with a Macroscopic Atomic Target

AbstractA theoretical analysis is presented on the photoexcitation of a macroscopic atomic target by a Hermite–Gaussian (HG) beam within the framework of density matrix theory. Special emphasis is paid to the influence of the incoming HG mode on the population of an excited state and the emitted fluorescence radiation. In particular, a general expression for the alignment parameter of the excited state is derived, which depends on the beam parameters of the HG mode. Although the developed theory can be applied to any atomic system, here the electric dipole transition in neutral sodium atoms is investigated when driven by three , and modes. For this optical (valence‐shell) excitation, it is demonstrated that the population of the excited state is sensitive to the beam waist and the mode index of the HG beam. Furthermore, the influence of beam parameters on the angular distribution and linear polarization of the emitted fluorescence radiation is discussed.

Effects of beam deviation on the mode purity of a vortex beam

The vortex beam has extensively demonstrated impressive significance in many applications. As a key parameter, the mode purity (MP) of a vortex beam is easily influenced by beam deviation. In this paper, the deviation models of the vortex beam — a beam wander model (BWM) and a phase singularity wander model (PSWM) are proposed. The MP expressions of these models are derived, and the influence of beam parameters on MP are studied through numerical methods. It is found that MP remains constant with the variation of azimuth of phase singularity, the maximally relative radial distance varies with the topological charge inversely and the influence of PSWM on MP is greater than BWM. Furthermore, the MP of a radially symmetrical vortex beam array is equal to that of each beamlet, and will increase with the decline of relative radial distance of each beamlet. The results can provide theoretical basis for further researches on orbital angular momentum (OAM) communication and vortex beam synthesis.

Analysis of the extension of optical filament in air based on phase-nested laser beam

Extending the length of femtosecond laser filament has always been desired for related atmospheric applications. Here we demonstrated that significant extension of filament can be achieved in air by using phase-nested beam which integrates the arise of filamentation and longitudinally extended background reservior in one optical beam. The influences of beam parameters on the length and uniformity of filament and corresponding physical mechanism are revealed. The energy extraction process from the background reservoir to the filament is investigated based on the evolution of pulse profile during the regeneration of filament. A fiber-like model is proposed to explain the capture effect of filament to the background reservior. Our theoretical results will be helpful to understand the mechanism of background reservior in the extending of filament, and may further guide the experimental design of phase-nested beam to achieve long and homogeneous filament in air.

Multi-layer structure formation of relativistic electron beams in plasmas

A two-dimensional electromagnetic particle-in-cell simulation model is proposed to study the density evolution and collective stopping of electron beams in background plasmas. We show here the formation of the multi-layer structure of the relativistic electron beam in the plasma due to the different betatron frequency from the beam front to the beam tail. Meanwhile, the nonuniformity of the longitudinal wakefield is the essential reason for the multi-layer structure formation in beam phase space. The influences of beam parameters (beam radius and transverse density profile) on the formation of the multi-layer structure and collective stopping in background plasmas are also considered.

Goos-Hänchen shift of an Airy beam reflected in an epsilon-near-zero metamaterial

We numerically investigated lateral Goos-Hänchen shifts a two-dimensional Airy beam experiences when it is reflected at the interface between air and an epsilon-near-zero metamaterial. Angular spectrum theory is employed to decompose Airy beam into plane waves, followed by beam vectorization to overcome the paraxial propagation assumption. The reflected light field can then be obtained by integrating plane waves weighted by Fresnel reflection coefficients. Results show that Airy beam experiences nonzero GH shift at normal incidence due to asymmetric angular spectrum. Influences of beam parameters and permittivity are further investigated. Our study provides foundation for deep understandings of Airy beam in epsilon-near zero metamaterials.

Nonparaxial propagation of a partially coherent four-petal Gaussian vortex beam

In the analysis of the nonparaxial propagation and far field propagation, the analytical propagation equations of a partially coherent four-petal Gaussian vortex beam have been derived based on the Rayleigh-Sommerfeld diffraction. The properties of nonparaxial propagation properties of a partially coherent four-petal Gaussian vortex beam have been obtained and analyzed using the numerical examples. And the influences of beam parameters on the average intensity of nonparaxial and far field propagation properties of partially coherent four-petal Gaussian vortex beam have been analyzed.

Average intensity and coherence properties of a partially coherent Lorentz-Gauss beam propagating through oceanic turbulence

Based on the Huygens-Fresnel integral and the relationship of Lorentz distribution and Hermite-Gauss function, the average intensity and coherence properties of a partially coherent Lorentz-Gauss beam propagating through oceanic turbulence have been investigated by using numerical examples. The influences of beam parameters and oceanic turbulence on the propagation properties are also discussed in details. It is shown that the partially coherent Lorentz-Gauss beam with smaller coherence length will spread faster in oceanic turbulence, and the stronger oceanic turbulence will accelerate the spreading of partially coherent Lorentz-Gauss beam in oceanic turbulence.

Simulation analysis of zinc ablation process and mass by intense pulsed ion beam irradiation

AbstractAs the strong thermal effect in the surface, intense pulsed ion beam (IPIB) has been extensively used in material surface modification. The ablation is an important part in the interaction process between IPIB and material. In order to investigate the ablation mechanism, combined with IPIB dynamic energy spectrum and infrared imaging diagnostic results, a two-dimensional axisymmetric heat conduction model considering the effect of ablated material was constructed to describe the ablation process and calculate the lost mass of the targets. The influences of beam parameters and ablated matter on the ablation rate were discussed. The experimental and simulative results of ablation threshold and mass were compared.

Influence of beam parameters and low-energy electron neutralization on wafer charging during ion implantation

In this paper charging caused by ion implantation is investigated using a fast-feedback, non-contact Kelvin-probe technique to measure the wafer surface potential. Arsenic and Boron implants were carried out varying the beam parameters and the degree of beam neutralization. It is found that the beam parameters do have an influence on charging if the degree of beam neutralization is low. In particular, charging increases with the beam current. Possible ways to reduce charging while maintaining high beam currents (and therefore high throughput) are discussed.

Influence of beam parameters on the laser induced particle emission from surfaces

For analysis of the laser induced plasma from graphite targets in high vacuum time-of-flight velocity distributions of ablated carbon ions have been measured. The previously observed linear relation between ion energy and laser energy density in the regime of nanosecond laser pulses is confirmed. Moreover, an enhancement of the laser spot size on the target results in higher kinetic ion energies in the same way as an increase of the laser energy density, being in accordance with standard ablation theories. The use of femtosecond laser pulses (500 fs, 248 nm) results in strongly enhanced kinetic energies of up to 10 keV at about 9 J/cm2, as compared to 50 eV at similar energy densities in the ns regime.

Pulsed laser deposition of electroceramic thin films

Sintered targets of BaTiO3 are ablated by KrF excimer laser radiation (λL = 248nm) with pulsed-laser deposition (PLD) in order to produce electroceramic thin films for dielectric and ferroelectric applications. Plasma formation and expansion is observed by a time-of-flight (TOF) setup with time-resolved (10 ns resolution) plasma emission spectroscopy (PES) in the 200 to 900 nm wave length range. Thin films with tetragonal crystalline structure and a dielectric constant up to 790 are deposited on Si(111)/Ti/Pt substrates. Ellipsometry is used to determine the influence of the laser cross-section geometry on the target surface on the film thickness homogeneity. The influence of beam parameters on particle speed in the plasma and on the electrical and structural properties of deposited films is presented. The chemical composition of the thin films as a function of processing variables is characterized by X-ray photoelectron spectroscopy (XPS). Crystalline structure is analysed by Raman-microprobe spectroscopy (RMP) and X-ray diffraction (XRD). Electrical characterisation is done by impedance measurements.