Electromagnetic Gaussian Beam Research Articles

Description of acoustical Gaussian beams from the electromagnetic Davis scheme of approximations and the on-axis localized approximation.

Electromagnetic Gaussian beams may be described by using a Davis scheme of approximations. It is demonstrated that this scheme also may be used, with minor changes, to manage the description of acoustical waves. The acoustical version of the Davis scheme afterward allows one to establish an efficient and accurate localized approximation to evaluate beam shape coefficients, which encode the structures of acoustical waves, similar to the localized approximation, which has been made famous when dealing with electromagnetic waves. The present paper is restricted to the case of on-axis beams.

Spectral and coherent properties of partially polarized pulsed electromagnetic beams upon turbulent atmosphere propagation for different source conditions

The spectral and coherent properties of partially polarized pulsed electromagnetic beams propagating in a horizontal homogeneous and isotropic turbulent atmosphere channel for different source conditions are investigated in detail. Based on the extended Huygens–Fresnel principle and von Karman power spectrum, the analytical expressions for the elements of the two-frequency cross spectral density matrix, the average spectral intensity, the beam width, and the spectral degree of electromagnetic coherence are derived in turn. Finally, with the help of numerical calculations, the effects of different source conditions on the changes in the beam width, spectral and coherent properties of partially polarized pulsed Gaussian Schell-model electromagnetic beams are studied. Some theoretical results in this paper will be useful for applications involving polarized pulsed electromagnetic beams propagating through atmospheric turbulence.

The nonlinear wave in semiconductor quantum plasma for laser beam in a self-consistent plasma channel

In this paper investigating the current task, our emphasis is on distributed a serious laser beam in a self-made plasma channel. As the intensity of the laser beam increases, the medium displays the neuromuscular electrical conductivity functioning as a result of the mass effectiveness of the effectiveness of the electrons as well as the intensity of the electrons. Based on Wentzel–Kramers–Brillouin and paraxial ray theory, the steady-state solution of an intense, Gaussian electromagnetic beam is studied. The differential equation of the distance with the beam width parameter is derived, including the relativistic effects of self-focusing (SF) and self-channeling ponder motive. Plasma propagation is a radial dynamical force, depending on the width of the beams and σp greater, plasma ratio frequency screws. Once the distribution regimes, the beam power beamwidth is obtained in plane. The σp is a particular value characterized by standard deviation, oscillation and diffusion regimes such as self focusing. The corresponding center parameters are intended for introduction of the plasma density curve and the laser beam is spatially analyzed to the spatial plasma. Performing this margin can lead to a long distance laser beam guide. The disadvantage of numerical predictions is done for laser plasma interaction studies for common factors.

Spatiotemporal evolution of Gaussian laser pulse in weakly relativistic magnetized cold quantum plasma

The paper presents the spatiotemporal evolution of electromagnetic Gaussian laser beam propagating in weakly relativistic plasma medium. We have applied axial magnetic field and by taking into account the quantum effects to study pulse compression and self-focusing mechanism of the incoming laser pulse. The coupled equations involving beam width and pulse length parameters are derived using paraxial ray and Wentzel Kramers Brillouin approximations. The numerical solution of the coupled equations are obtained using fourth-order Runge-Kutta method which determine the beam dynamics in both time and space in different type of plasma medium. The results obtained illustrates that the pulse is compressed to a significant extent as it propagates through plasma thereby enhancing the normalized intensity of the pulse to many folds when quantum effects are taken in addition to the magnetic field as compared to the case when magnetic field alone is taken into account and neglecting quantum effects. It is further observed that self-compression mechanism assists the self-focusing of the pulse and hence we get highly focused pulse with lesser spot size. Three-dimensional view of spatiotemporal profile of normalized intensity has been plotted at different focusing and defocusing points of laser pulse which presents the comprehensive picture of pulse compression and self-focusing with the normalized distance of propagation.

Generation of terahertz (THz) radiation by p-polarised lasers beating in hot plasma with surface density ripple

The present communication deals with a scheme to generate terahertz (THz) radiation by electromagnetic Gaussian beams beating in a hot collisionless plasma having a density ripple on its surface, parallel to the z-axis. These p-polarised laser beams propagate in the x-z plane, incident obliquely to the density ripple on the plasma surface, and exert a ponderomotive force on electrons. The plasma electrons start oscillating because the plasma neutrality disturbed by the nonlinearity arises due to the ponderomotive force. This oscillatory velocity beats with the density ripple; as a result, an irrotational current density arises at the beating frequency (with ). This nonlinear current density urges a wave whose frequency is in the THz range. Our results show that, for a set of laser and plasma parameters, the power of emitted THz radiation scales as the square of the density ripple amplitude, as well as the amplitude of the emitted THz wave, decreases with the THz frequency and increases with the incidence angle up to an optimum value. In our case, the maximum normalised amplitude of emitted THz radiation is reached up to 0.038 at laser intensity ~7 × 1014 W cm−2, and electron temperature ~5 keV with 30% density ripple.

Theoretical model for the effect of dust grains on self‐filamentation of a gaussian electromagnetic beam in a fully ionized plasma

A theoretical model for the effect of dust grains on the self‐filamentation of a Gaussian electromagnetic beam propagating in a fully ionized plasma has been developed by employing the energy balance of the plasma constituents, perturbed electron and ion concentrations, and temperature. In this model, neutral atom ionization, re‐integration and accumulation of electrons and ions, photoelectric emission of electrons from the surface of dust grains, as well as elastic and charging collisions have also been considered. The effective dielectric constant in the presence of dust grains has been constructed. The effect of temporal growth of dust grains on various plasma parameters for different values of the dust density has been explored. The variation of the beam width with the normalized channel of propagation has been observed for distinct dust densities and dust charge states. It is observed that the non‐linearity induced by the effective dielectric constant in the presence of dust grains increases the self‐filamentation of the beam, thus enhancing the effective critical power with the dust density. Some of the outcomes of our approach are in line with experimental observations. These outcomes may be useful for explaining space and laboratory plasma experiments as well as for future studies in complex plasmas.

Propagation of Correlation Singularities of a Partially Coherent Laguerre–Gaussian Electromagnetic Beam in a Uniaxial Crystal

The correlation singularities of a partially coherent Laguerre–Gaussian (LG) electromagnetic beam in a uniaxial crystal is shown to possess interesting evolution behavior. The analytical formula for the cross-spectral density matrix of a partially coherent LG electromagnetic beam propagating in a uniaxial crystal orthogonal to the optical axis is derived. It is found that the correlation singularities of a partially coherent LG electromagnetic beam in a uniaxial crystal is closely determined by the spatial coherence and mode orders of the beam, and the refractive indexes of the crystal. For a partially coherent LG electromagnetic beam, the correlation singularities can propagate further in a uniaxial crystal than that in isotropic medium. For a fully coherent LG electromagnetic beam, in isotropic medium the central correlation singularities and circular edge dislocations persist upon propagation; in a uniaxial crystal the circular edge dislocations become imperfect, and the central correlation singularities with topological charges $l \ne 1$ split up into correlation singularities with topological charges equaling 1.

Beam wander and M2-factor of partially coherent electromagnetic hollow Gaussian beam propagating through non-Kolmogorov turbulence

Propagation formulae for M2-factor and beam wander of partially coherent electromagnetic hollow Gaussian (PCEHG) beam in non-Kolmogorov turbulence are derived based on the extended Huygens–Fresnel principle and the second-order moments of the Wigner distribution function. Our results indicate that the normalized M2-factors of PCEHG beam with larger beam order, waist width, inner scale of turbulence, the generalized exponent parameter, and smaller transverse coherent widths, outer scale of turbulence, the generalized structure parameter are less affected by the turbulence. The root mean square beam wander and relative beam wander are more obvious for PCEHG beam with smaller beam order, larger inner and outer scales of turbulence, exponent parameter, transverse coherent widths, and the generalized structure parameter. What is more, the beam wander properties of PCEHG beam in non-Kolmogorov turbulence are very different from M2-factor and spreading properties of beam in turbulence.

Self-focusing of coaxial electromagnetic beams in a plasma with electron temperature dependent electron-ion recombination coefficient

An analytical formulation, describing the propagation of multiple coaxial Gaussian electromagnetic (em) beams in a self-formed plasma channel with dominant collisional nonlinearity has been developed; the generation/recombination of high energy plasma particles has been considered as an additional source of plasma non-linearity in addition to Ohmic heating. Well versed paraxial approach in the vicinity of the intensity maximum has been adopted to solve the wave equation and examine the non-linear propagation of em beams while the dielectric function in the presence of the em field is determined from the balance of partial pressure gradient of electron/ion gas with the space charge field and energy balance of plasma particles. On the basis of the analysis the influence of this novel non-linearity on the propagation features like electron temperature, dielectric function and critical curves are derived numerically and graphically presented. The inclusion of this novel nonlinearity results in reduced focusing effect. The three regime characteristic features viz. oscillatory focusing/defocusing and steady divergence of beam propagation have also been worked out.

Light scattering by a cluster consisting of homogeneous axisymmetric particles illuminated with an arbitrarily focused electromagnetic Gaussian beam

Scattering of an arbitrarily focused electromagnetic Gaussian beam by a chain cluster consisting of axisymmetric particles is presented. The illustrated technique in this paper combines the plane-waves spectrum method and the cluster T-matrix calculation technique. This combination provides a powerful mathematical and numerical tool to solve such types of scattering problems. Computed results are shown for different particles shapes in the cluster and for different beam focusing.

Thermal Action of a Gaussian Beam of Electromagnetic Waves

The action of a Gaussian electromagnetic beam on a dielectric medium is investigated in the linear approximation. The dielectric properties of the medium are described by the Debye polarization model. Boundary conditions for normal incidence of a Gaussian beam are formulated. The distributions of the specific absorbed power and of the temperature in the dielectric medium are found.

Coaxial propagation of Laguerre–Gaussian (LG) and Gaussian beams in a plasma

AbstractThis paper investigates the non-linear coaxial (or coupled mode) propagation of Laguerre–Gaussian (LG) (in particular L01 mode) and Gaussian electromagnetic (em) beams in a homogeneous plasma characterized by ponderomotive and relativistic non-linearities. The formulation is based on numerical solution of non-linear Schrödinger wave equation under Jeffreys–Wentzel–Kramers–Brillouin approximation, followed by paraxial approach applicable in the vicinity of intensity maximum of the beams. A set of coupled differential equations for spot size (beam width) and phase evolution with space corresponding to coupled mode has been derived and numerically solved to determine the propagation dynamics. Using focusing equation a critical condition describing the self-trapped (i.e., spatial soliton) mode of laser beam propagation in the plasma has been discussed; as a consequence oscillatory focusing/defocusing of the beams in coupled mode propagation have been analyzed and presented graphically. As an important outcome, significant enhancement in the intensity of LG beam is noticed when it is coupled with the Gaussian mode.

Relativistic self-focusing of ultra-high intensity X-ray laser beams in warm quantum plasma with upward density profile

The results of a numerical study of high-intensity X-ray laser beam interaction with warm quantum plasma (WQP) are presented. By means of an upward ramp density profile combined with quantum factors specially the Fermi velocity, we have demonstrated significant relativistic self-focusing (RSF) of a Gaussian electromagnetic beam in the WQP where the Fermi temperature term in the dielectric function is important. For this purpose, we have considered the quantum hydrodynamics model that modifies refractive index of inhomogeneous WQPs with the inclusion of quantum correction through the quantum statistical and diffraction effects in the relativistic regime. Also, to better illustration of the physical difference between warm and cold quantum plasmas and their effect on the RSF, we have derived the envelope equation governing the spot size of X-ray laser beam in Q-plasmas. In addition to the upward ramp density profile, we have found that the quantum effects would be caused much higher oscillation and better focusing of X-ray laser beam in the WQP compared to that of cold quantum case. Our computational results reveal the importance of the use of electrons density profile and Fermi speed in enhancing self-focusing of laser beam.

Enhanced propagation and focusing of an intense laser beam in high density magnetized plasma

In the present communication, the steady state propagation of an intense, circularly polarized Gaussian electromagnetic beam in high-density magnetized plasma is studied analytically and numerically. The relativistic oscillation of the mass of the electrons in the field of the pump and longitudinal magnetic field are shown to have a major effect on the dynamics of the propagation of intense electromagnetic wave. The wave equation has been solved under WKB and paraxial approximation by expanding the dielectric tensor for arbitrary large intensity. The propagation of electromagnetic waves in magnetized plasma, in the so-called extraordinary mode has been explicitly considered in the analysis. The variation of beamwidth parameter with distance of propagation has been obtained for chosen values of critical parameters in different regimes. These regimes are steady divergence, oscillatory divergence and self-focusing. Numerical computations are performed for a wide range of dimensionless parameters. It is seen that the laser beamwidth tends to attain a constant value depending upon plasma electron density, axial inhomogeneity and laser irradiance for different strength of magnetic field. Further, enhanced propagation, focusing and penetration of an intense laser beam is evident through plots from slightly underdense to overdense plasma with different types of density profiles.

Distribution regimes of intense laser beam in a self-consistent plasma channel

In the present work, we investigate the distributed regimes of an intense laser beam in a self-consistent plasma channel. As the intensity of the laser beam increases, the relativistic mass effect as well as the ponderomotive expulsion of electrons modifies the dielectric function of the medium due to which the medium exhibits nonlinearity. Based on Wentzel–Kramers–Brillouin and paraxial ray theory, the steady-state solution of an intense, Gaussian electromagnetic beam is studied. A differential equation of the beamwidth parameter with the distance of propagation is derived, including the effects of relativistic self-focusing (SF) and ponderomotive self-channeling. The nature of propagation and radial dynamics of the beam in plasma depend on the power, width of the beam, and Ωp, the ratio of plasma to wave frequency. For a given value of Ωp (<1), the distribution regimes have been obtained in beampower–beamwidth plane, characterizing the regimes of propagation as steady divergence, oscillatory divergence, and SF. The related focusing parameters are optimized introducing plasma density ramp function, and spot size of the laser beam is analyzed for inhomogeneous plasma. This results in overcoming the diffraction and guiding the laser beam over long distance. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction studies.

Effect of source parameters on polarization characteristics of electromagnetic beam propagating in atmospheric turbulence

According to the theory of beam spreading and taking electromagnetic Gaussian Shell-model beam as an object of research, the change in its spectral degree of polarization is studied by numerical analysis. Based on the numerical results, the mechanism that governs the change in polarization of an electromagnetic beam on propagation is discussed. The results show that the beam spreading of two components of an electromagnetic beam results in the change in polarization of beam directly, and the beam spreading is determined by source parameters and atmospheric turbulence. The difference between beam spreading of two components induced by coherence leads to the change in polarization in free space. The change in degree of polarization is influenced by source parameters and turbulence on propagation in atmosphere. The result is similar to that in free space over relatively short distance, which is mainly governed by source parameters. With the enhancement of turbulence over a sufficiently long distance, the change in polarization in atmosphere is different from that in free space.

Performance of a New Bundle Fiber Sensor of 1000 RF in Comparison With 16 RF Probe

The comparison of bundle sensor performance between 16 concentric receiving fiber (RF) and 1000 hemicircular RF probes is reported. A theoretical analysis is developed for 1000 RF to support the experimental findings, which uses an electromagnetic Gaussian beam approach to determine the transfer function of the probe. Three linear ranges of the displacement profile can be obtained from each probe, namely, the front slope, the first back slope, and the second back slope. The highest sensitivity obtained by the 16 concentric RF at the front slope range is 5.8148 mV/mm with a resolution . Its lowest sensitivity at the second back slope region is 0.06 mV/mm with an initial resolution of 26 μm. The 16 RF probe produces a better sensor performance both at the front slope and the first back slope region, whereas at the second back slope region, the 1000 RF exhibits a higher sensitivity. Furthermore, a wider linear range is realized through the 1000 RF whereby the front slope and the first back slope are 1.45 and 4.75 mm, respectively. The second back slope of the 16 RF, however, provides a longer linear range 3.0 mm. The latter sensor probe has many potential applications in the longer displacement range, such as position control, micro-displacement sensing in hazardous regions, and automated monitoring control.

Self-focusing of a Gaussian electromagnetic beam in a multi-ions plasma

In this paper, the authors have developed a formulation for the dependence of electron and ion densities on the irradiance of an electromagnetic beam in a plasma with multiply charged ions, corresponding to collisional, ponderomotive, and relativistic-ponderomotive nonlinearities and different electron/ion temperatures; consequently, the corresponding expressions for the electron density modification in the presence of an electromagnetic (em) field have been derived. Paraxial approach in the vicinity of intensity maximum has been adopted to analyze the propagation characteristics of an em beam in such plasmas; on the basis of this analysis, critical curves and self-focusing curves have been computed numerically and graphically illustrated. For a numerical appreciation of the analysis, we have specifically carried out the computations for the simultaneous presence of singly and doubly charged ions in the plasma. As an important outcome, it is seen that the nonlinear effects (and hence self-focusing) get suppressed in the presence of multiply ionized ions; the conditions for the three modes of em-beam propagation viz. oscillatory focusing/defocusing and steady divergence have been discussed.

Interaction between parallel Gaussian electromagnetic beams in a plasma with weakly relativistic-ponderomotive regime

In this communication, authors have studied the interaction between two Gaussian electromagnetic beams in a plasma for weakly relativistic-ponderomotive regime when the axes of two beams are initially parallel along z-axis in the xz plane: the beams are initially propagating in the z-direction. Second order coupled ordinary differential equations have been obtained for the distance between centers of the beams and the beam widths in the x- and y-directions along z-axis. The so obtained equations are solved numerically for a range of parameters and the results are depicted in the form of graphs.

Gaussian Beam Summation Representation of Beam Diffraction by an Impedance Wedge: A 3D Electromagnetic Formulation Within the Physical Optics Approximation

We present a beam summation (BS) representation for the field scattered by an impedance wedge illuminated by a general 3D electromagnetic Gaussian beam (EM-GB). The emphasis here is not only on the solution of the beam diffraction problem, but mainly on the BS representation. In this representation, the field is expressed as a beam optics (BO) term plus an edge field, described as a sum of diffracted EM-GB's emerging from a discrete set of points and directions along the edge. We introduce an edge-fixed set of EM-GB's that provides a basis for the edge field. The expansion coefficients (the beam's excitation amplitudes) account in a dyadic format for the polarization of the incident beam and also for its direction, displacement from the edge, collimation, and astigmatism. We derive exact expressions for these coefficients as well as simpler approximations that are valid uniformly as a function of the incident beam distance from the edge. The results of this paper provide essential building blocks for a BS representation of EM fields in complex configurations, where the source excited field is described as a sum of beam propagators, and the diffracted fields generated by propagators that hit near edges are also described using beams.