super-Gaussian Laser Beam Research Articles

Electrostatic wave assisted super-gaussian laser beam absorption in collisional plasma embedded with static magnetic field

Electrostatic wave assisted super-gaussian laser beam absorption in collisional plasma embedded with static magnetic field

Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

Electron Bernstein wave aided heating of collisional nanocluster plasma by nonlinear interactions of two super-Gaussian laser beams

In this present theoretical study, we investigate electron Bernstein wave (EBW) aided collisional nanocluster plasma heating by nonlinear interaction of two super-Gaussian laser beams. The interactions of laser beams electric field profiles with electronic clouds of nanoclusters cause the beat wave. The nonlinear ponderomotive force is generated through the beat wave. There may be good potential to excite the EBW aiding cluster plasma to lead electron heating via cyclotron damping of the Bernstein wave. An analytical scheme is proposed for the anomalous heating and evolution of electron temperature by using this mechanism. Graphical discussions were promised to achieve extreme heating rate via the spatial shape of super-Gaussian laser beams and the resonance condition of beat wave to surface plasmon frequency. The heating is controlled by tuning the laser beam width, mode index, collisional frequency, clustered radius, and density.

Spatial evolution leading to multiple filament formation of higher order super Gaussian beam in bulk medium at input power P >>Pcr

Multiple filamentation in higher order super Gaussian laser beam propagating in chalcogenide glass is investigated by numerically solving nonlinear Schrödinger equation with split step beam propagation method at input power range of 40 – 160 Pcr and compared to the process in super Gaussian beam. The effect of raising the beam order on the deterministic nature of multiple filaments, threshold power of filamentation, length of filamentation and the number of filaments formed are analysed. The results indicate that within a range of beam order and input power, the process of multiple filamentation in super Gaussian beam may be controlled through beam order. The study further exemplifies the importance of deterministic filaments and the ‘role of beam order as a tool’ in control of self-guided laser beam properties in filamentation process.

Kerr lens effect induced by a super-Gaussian laser beam

Recently, a new type of laser cavity has been proposed. It includes two Diffractive Optical Elements set inside the resonator against the cavity mirrors in order to achieve the structuring of the fundamental mode. The latter is a perfect Gaussian beam (M2 = 1) from the output mirror side, and super-Gaussian in the amplifying medium. Such a special cavity allows for improving the energy extraction, and it should be interesting to mode-lock such a laser cavity by using the KLM technique. For that, we aim to model the Kerr lensing effect, induced by a super-Gaussian beam. An analytical expression for the Kerr focal length has been deduced from a Zernike polynomial development. The obtained results are in a good agreement with a diffraction analysis.

Electron Bernstein wave excitation by beating of two copropagating super-Gaussian laser beam in a collisional nanocluster plasma

An analytic formalism is developed to study electron Bernstein wave excitation by two copropagating high power super-Gaussian laser beams in a collisional nanocluster plasma. The medium is assumed to contain spherical plasma plume ball of nanocluster. As the electric field of two laser beams interact with nanoclustered plasma, it would cause the beat wave frequency ω=ω1−ω2. The laser beat wave exerts a nonlinear pondermotive force on electron cloud of clustered plasma that in turns lead to excite the electron Bernstein wave in the laser field polarizations direction. The effective finite y-component of the beat wave experiences group velocity and it might cause convective losses. The spatial shape of electron Bernstein wave normalized potential and power profile promises better excitation mechanism in nanoclustered plasma as compared to only plasma medium. It is observed that excitation is much enhanced when the laser beat frequency lies near the effective plasmons frequency of nanoclustered plasma. The excitation is detuned by varying the laser mode index, clustered radius, collisional frequency, parameter b. One may apply this theory of electron Bernstein wave excitation in toroidal fusion devices.

Tunable terahertz radiation generation using the beating of two super-Gaussian laser beams in the collisional nanocluster plasma

In this paper, generation of terahertz (THz) radiation by the beating of two super-Gaussian laser beams in a nanocluster plasma is investigated, theoretically. The electric field of laser beams interacts with the nanocluster, leads to the ionization of the cluster atoms, and produces nanoplasma. Interaction of laser beams with the electronic clouds of nanoplasma generates ponderomotive force that leads to the creation of a macroscopic electron current at the beat frequency, which can generate THz radiation. The THz wave equations and THz efficiency in the nanoplasma medium were analytically derived and then numerically discussed. The effects of the density and radius of nanoclusters, the laser beam width, and intensity of super-Gaussian lasers on the THz radiation efficiency have been investigated in the nanoplasma-based THz emitter. The results indicated when the beat-wave frequency approaches the effective plasmon frequency of the nanoplasma, the maximum value of the field amplitude of THz radiation is acquired. In addition, it was found that the best situation that can be obtained is the THz radiation occurring at frequency ω = ω p / 3 .

Terahertz emission during laser-plasma interaction: effect of electron temperature and collisions

The electron-neutral collisions in the plasma become crucial with regard to the generation of THz radiation when thermal motion of the electrons is considerable. If we look at the mechanism of THz emission, this is only the movement/oscillations of the electrons which is responsible for the excitation of nonlinear current that generated the THz radiation. The present work aims to disclose the role of thermal motion of the plasma electrons to the resonance condition and the THz emission when two co-propagating super-Gaussian laser beams beat in the plasma. The dynamics of the plasma electrons and subsequent generation of nonlinear current are discussed in greater detail for the emission of THz radiation.

Self-defocusing of super-Gaussian laser beam in tunnel ionized plasmas

Based on moment theory, an analytical formalism of high intensity super-Gaussian laser beam propagation through a tunnel ionized gas is developed by including the effects of diffraction divergence and nonlinear refraction. During the interaction of the laser with the plasma, the plasma density is found to have a broad maximum on the axis in the direction of propagation of the laser, causing self defocusing of the laser beam. It is seen that the super-Gaussian beam suffers stronger divergence than a Gaussian beam. The laser beam is found to get more defocused for the cases of higher intensity and smaller spot size of the laser. For in depth study, the calculations are carried out for argon, neon and xenon gases and it is seen that different gases lead to different diffraction divergence.

Self-focused amplitude modulated super Gaussian laser beam in plasma and THz radiation with high efficiency

Based on self- focusing of an amplitude modulated super Gaussian laser beam in preformed ripple density plasma, one scheme can be proposed for generating terahertz (THz) radiation at the modulation frequency when pondermotive nonlinearity is operative. The eikonal in paraxial ray approximation (PRA) along with higher order terms in the expansion of the dielectric function have been taken into account. Intensity variation in the direction transverse to the propagated laser causes a pondermotive force which generates transient transverse nonlinear current. At the modulation frequency, the mentioned current drives radiation in THz domain. Therefore, comparing to simple PRA, inclusion of terms with higher order enhances beam self-focusing, THz radiation field and, efficiency. In addition, the degree of the self-focusing is reduced in higher laser beam orders and has changed by the modulation index and the time. Here, by considering higher order paraxial ray approximation and optimizing laser beam and ripple density, plasma parameters are investigated and the efficiency of THz radiation reaches up to 6.5%. This method can be applied for the efficient types of THz radiation.

Relativistic self focusing and frequency shift of super-Gaussian laser beam in plasma

Relativistic self focusing and frequency shift of laser beam having super-Gaussian profile in space and Gaussian profile in time is studied in a plasma. The relativistic mass nonlinearity is found to cause time dependent self focusing of the laser pulse and the saturation effect of nonlinearity avoids point focusing of the beam. For ultrashort laser pulse, the front of the pulse undergoes frequency down shift while that of the tail undergoes up shift. Frequency shift increases and self focusing becomes stronger for higher intensity of the laser. The self focusing is also stronger for the laser beam carrying larger wavelength.

Role of magnetic field on self focusing of super-Gaussian laser beam under relativistic effect

Considering an external magnetic field along the direction of propagation of laser, the self focusing of a super-Gaussian laser beam is studied when it propagates through the plasma at relativistic intensities. We consider the cyclotron motion of the electrons and use the tensor form of the plasma dielectric constant obtained based on the direction of the external magnetic field. For completeness, relativistic mass effect is incorporated in both the plasma frequency and electron cyclotron frequency. Using appropriate conditions, an equation for the beam width parameter is derived and solved. The equilibrium beam radius for a self trapped laser beam is also derived. Self focusing is better when cyclotron effects are taken into account. At higher intensity and higher spot size of the laser beam, self focusing becomes better.

Strong Terahertz radiation generation via wakefield in collisional plasma

The present calculations show that the application of an external magnetic field can generate additional component of the wakefield suitable for Terahertz (THz) radiation generation in a collisional plasma. Based on the approach of perturbation technique under quasi-static approximation, a study is made on the field of emitted radiation pulses from the wakefield when the super-Gaussian laser beams are used. The field of the radiation becomes stronger when stronger magnetic field is applied and the same is the case for the lasers of higher index.

Laser wakefield accelerator driven by the super-Gaussian laser beam in the focus

The injection process is one of the most crucial attributes that determine the final properties of the electron bunch in laser wakefield accelerators. Here, a new injection method is proposed and studied via particle-in-cell simulations for the typical parameters of the bubble regime. The injection is triggered by the laser beam that reaches the super-Gaussian profile in the focus. Such a beam undergoes rapid variations in its intensity distribution during the diffraction process. If this diffraction occurs in underdense plasma, consequent changes in the bubble structure activate a localized transverse injection process. The generated electron bunch is characterized by the short duration (∼2 fs) and low transverse emittance (≤1 mm mrad) while maintaining relatively high charge (∼0.2 nC).

Resonant third harmonic generation of super-Gaussian laser beam in a rippled density plasma

Resonant third harmonic generation of super-Gaussian laser beam in rippled density plasma is studied. Both the relativistic and ponderomotive nonlinearities are included in the analysis, and the study is done for self-guided laser beam. The quasi-static component of ponderomotive force creates electron density depression in the beam region while the second harmonic component leads to second harmonic density oscillations, leading to third harmonic generation. The relativistic mass variation supplements these processes with same order of contributions. The ripple provides the phase matching and requisite ripple wave number decreases with the frequency of the laser.

High-power terahertz radiation generation by beating of two co-propagating super-Gaussian laser beams in cluster plasma

This communication presents the theoretical investigation of resonant terahertz (THz) radiation generation by two co-propagating laser beams having super-Gaussian intensity profile in a clustered plasma. The cluster electrons experience a ponderomotive force at beat wave frequency in the axial direction as well as perpendicular to the propagation direction of the beams due to the nonuniform intensity profile of laser beams. This force causes the acquisition of a nonlinear oscillatory velocity to the cluster electrons. A strong nonlinear transverse current density at beat wave frequency arises on account of the coupling of nonlinear velocity with density ripple, which drives a THz wave in the propagation direction of the laser beam. The THz yield strongly depends on the index of the super-Gaussian beams as well as the amplitude of density ripple. We report generated THz wave efficiency of 10−3 with the help of the optimizing laser beams and cluster plasma parameters.

Terahertz radiation generation by beating of two laser beams in a collisional plasma with oblique magnetic field

A scheme for excitation of terahertz (THz) radiation is presented by photo mixing of two super-Gaussian laser beams in a rippled density collisional magnetized plasma. Lasers having different frequencies and wave numbers but the same electric fields create a ponderomotive force on the electrons of plasma in the beating frequency. Super-Gaussian laser beam has the exclusive features such as steep gradient in laser intensity distribution, wider cross-section in comparison with Gaussian profiles, which make stronger ponderomotive force and higher THz radiation. The magnetic field is considered oblique to laser beams propagation direction; in this case, depending on the phase matching conditions different mode waves can propagate in plasma. It is found that amplitude and efficiency of the emitted THz radiation not only are sensitive to the beating frequency, collision frequency, and magnetic field strength but to the angle between laser beams and static magnetic field. The efficiency of THz radiation can be o...

On validity of paraxial theory for super-Gaussian laser beams propagating in a plasma

In the present paper, we have investigated a situation where a high intensity laser beam passes through a gas and ionizes this gas by tunnel ionization. Here the electric field of the laser provides a sufficient velocity to the electrons to surpass the Coulomb barrier of the atom. Owing to the ionization the plasma density enhances which affects the laser beam propagation. The use of paraxial ray approximation theory for the present case of super-Gaussian lasers reveals the self-focusing of the beams and frequency upshifting. The predicted self-focusing of the laser beams is contrary to the expected outcome of defocusing of these beams in the plasma, indicating that the paraxial theory may not be valid for the case of super-Gaussian lasers even for the inclusion of most of the near axis region in the theory.

High-power terahertz emission in magnetized plasma via optical rectification of a super-Gaussian laser beam

The paper discusses the generation of terahertz (THz) wave via the optical rectification of an amplitude-modulated super-Gaussian laser beam in the preformed periodic density plasma when a magnetic field is applied transversely. The non-uniform spatial variation in intensity of the laser beam drives a strong ponderomotive force. Such ponderomotive force generates nonlinear oscillatory drift velocity to plasma electrons that produce a strong transverse nonlinear current at the modulation frequency (the frequency of the radiation lies in the THz domain). Moreover, the presence of the periodic density plasma structure and magnetic field can shift the condition of resonance and can produce the tunable THz frequency radiation. In the current scheme, the THz field amplitude increases with the profile index of the laser, modulation index, ripple parameters, and transversely applied static magnetic field. As a result, the efficiency of the generated THz wave can be achieved of the order of for the exact phase-matching condition.

Terahertz radiation with high power and high efficiency in a magnetized plasma

We propose a scheme for the generation of terahertz (THz) radiation in a plasma by beating of two flat-topped laser beams when a static magnetic field is applied to the plasma with a parallel or perpendicular direction. We show that the presence of a static magnetic field can enhance drastically the power and efficiency of THz radiation. The power and efficiency enhancement of the perpendicular magnetic field is greater than that of parallel one. Furthermore, the perpendicular magnetic field produces THz radiation with a square shaped field profile which has many applications in industries especially in optical communication. Optimizing the laser beams and magnetized plasma parameters and considering the interaction (mutual effect) between laser beams, THz radiation, and plasma, the THz radiation efficiency up to 8.3% can be obtained. A comparison between the THz radiation generated by flat-topped and super Gaussian laser beams shows that, at the same conditions, the THz radiation generated by flat-topped beam lasers has some advantages such as about two times wider flat-topped region and more than two times higher efficiency.