Rippled Density Plasma Research Articles

Operation of free-electron lasers using spherical whistler and rippled density plasma

Operation of free-electron lasers using spherical whistler and rippled density plasma

Far IR field generation by mixing of cosh-Gaussian and dark hollow Gaussian laser in encapsulated plasma

A scheme of laser-plasma interaction is proposed by mixing of Cosh Gaussian (ChG) and Dark Hollow Gaussian (DHG) laser in rippled density plasma when an external periodic electric field wiggler is applied because of the emission of far infrared field lying in the terahertz frequency regime. The unusual mixing of ChG and DHG laser broadens the field of THz radiation from unifocal to multifocal by controlling beam order and decentralized parameters. Moreover, the wiggler field wavenumber provides two additional resonance conditions, which govern the emission of multiple components of far IR field resonantly that may have extensive medical applications. The field amplitude of such emissions and their efficiency may be increased manifold. Moreover, the efficiency can be increased several times if parallel plates are placed with a few nanometers of separation.

Propagation characteristics of relativistic ultrashort laser pulse in inhomogeneous plasma

We study the propagation of a relativistic ultrashort laser pulse in two-dimensional inhomogeneous plasma with a density ripple based on the theoretical analysis and the particle-in-cell simulation. An analytical solution of the laser pulse propagating in the homogeneous plasma is completely obtained. It is found that the stable propagation of the relativistic ultrashort laser pulse in homogeneous plasma can be realized, and the propagation distance and intensity of the laser pulse and the spatial distribution of electron density can be effectively modulated by adjusting the pulsewidth of the incident laser and the plasma frequency. More interestingly, in the inhomogeneous plasma with a density ripple, when the wave amplitude of the density ripple is less than a critical value, the intensity of the ultrashort laser pulse is almost unchanged and the propagation characteristics of the laser in the inhomogeneous plasma are basically consistent with those in the homogeneous plasma. However, when the wave amplitude of the density ripple is larger than the critical value, the inhomogeneity of the plasma has an obvious effect on the laser characteristics, and the intensity and the spatial distribution of the laser pulse will be modulated by the plasma density ripple. The influence of the laser pulsewidth, plasma density, and plasma density ripple on the laser characteristics is discussed in detail.

Terahertz Radiation Generation by Frequency Mixing of Hermite–Cosh–Gaussian Laser Beams in Density-Modulated Cold Magnetized Plasma

We report a theoretical investigation for extremely bright terahertz (THz) radiation generation by mixing of dichromatic Hermite–Cosh–Gaussian (HChG) laser beams in periodically rippled density plasma in the presence of external dc magnetic field. The magnetic field is applied perpendicular to the direction of propagation and to the polarization states of laser beams. THz field amplitude significantly increases with applied dc magnetic field. Our investigations reveal that frequency resonance shifts with the applied magnetic field. As a result, THz frequency tuning is possible with applied magnetic field. The electron neutral collisions have no effect on resonance condition but THz amplitude and efficiency decreases with increase in frequency of electron neutral collisions. We find that THz field profile strongly depends on laser parameters like Cosh decentred parameter $b$ and order of Hermite function $s$ , and independent of applied magnetic field. Our theoretical investigations predict that GV/m THz field with efficiency ~7% for laser field ~50 GV/m and 80-kG applied dc magnetic field can be obtained for optimized set of laser and plasma parameters.

Dynamics of resonant self‐focusing on second harmonic generation of Gaussian laser beam in a rippled density plasma

AbstractResonant second harmonic generation by a Gaussian laser beam in a rippled density plasma is studied using the moment theory approach. The nonlinearity arises through the relativistic mass effect and ponderomotive forces. The laser beam creates a plasma channel and gives rise to electron density perturbation at the laser frequency. The density perturbation beats with electron quiver velocity to produce second harmonics. The ripple provides phase matching and makes the process a resonant one. The second harmonic power efficiency is increased effectively with density ripple. Self‐focusing causes enhancement in the efficiency of harmonic generation.

High-Field Coherent Terahertz Radiation Generation From Chirped Laser Pulse Interaction With Plasmas

This article presents a theoretical analysis of high-field terahertz (THz) radiation generation from chirped laser pulse interaction with a plasma of slanting density modulation. The mechanism is based on strong nonlinear transverse current produced by the beating of two chirped laser pulses, where the plasma density modulation is inclined at angle to the propagation of the lasers. We claim that oblique spatial density ripple plays a crucial role in field enhancement of THz. At resonance (due to the phase-matching), the field strength of THz becomes maximum for a particular slating angle of the plasma density modulation. We claim that the oblique spatial density ripple and laser frequency-chirp combinedly play a crucial role in field enhancement of THz field. We observe that stable THz is generated with a maximum field strength of 100 MV/cm and a relatively broad spectrum extending out to 2.4 THz, with a strong dependence on the selection of slating angle of plasma density ripple and laser frequency chirp parameter, which corresponds to the conversion efficiency in order of 10−2. The efficiency of the process may be optimized and controlled by the laser and plasma parameters, which may be useful in various applications of these kind of high-field THz.

Power and efficiency enhancement of THz radiation in a plasma by dark hollow laser beams: Effects of magnetic field

The power and efficiency of terahertz radiation (THz) in a rippled density plasma by dark hollow laser beams are very small due to the collisional effect. We show that when a magnetic field is applied perpendicularly to the plasma, the THz radiation power and efficiency significantly enhance. Also, the magnetic field changes the THz radiation profile to a profile similar to a dark hollow laser beam. The mutual effect between the laser beams and THz radiation in plasma, which is important in high energy transfer between laser beams and THz radiation, is taken into account. We find that the maximum efficiency obtained in our scheme is more than four orders of magnitude greater than the efficiency in the absence of magnetic field.

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.

Non‐paraxial theory of self‐focusing/defocusing of Hermite cosh Gaussian laser beam in rippled density plasmas

AbstractPresent research work focuses on study of self‐focusing and self‐trapping of Hermite cosh Gaussian (HchG) laser beams in rippled density plasma by considering relativistic non‐linearity. The coupled non‐linear differential equations for the beam width parameters (for modes m = 0, 1, and 2) were derived by employing higher‐order correction in comparison to paraxial ray theory by expanding dielectric function and eikonal up to r4 terms. It is observed that the inclusion of higher‐order terms significantly influence the off‐axial properties for m ≥ 1 mode indices. Furthermore, the effect of parameters including beam intensity, ripple factor, depth of density modulation, and decentred parameter on self‐focusing and self‐trapping is analysed and discussed both analytically and numerically.

The influence of static magnetic field on nonlinear response of a plasma background in the presence of two laser beams with different profiles (Hermite– and Laguerre–Gaussian)

This paper presents a theoretical study on terahertz (THz) radiation produced by the nonlinear interaction of two laser beams of Laguerre–Gaussian and Hermite–Gaussian profiles with axially magnetized ripple density plasma. The influence of the external magnetic field on the optimization process of the THz field amplitude and on the field profile of the emitted THz wave are investigated. Due to the dispersion and anisotropy of the magneto-active plasma medium, the effect of beat frequency on the electric field amplitude of THz radiation is also examined. The results reveal that the external magnetic field can enhance the THz field amplitude without significantly affecting the THz field profile.

Investigation of power density absorption in rippled density plasma toward THz generation

In the present paper by applying a two-color linear polarized laser in rippled density plasma, the density of absorbed energy has been investigated using the two-dimensional particle-in-cell method and its role on THz generation in resonance and non-resonance schematic has been studied. Interplaying of time dependence of two lasers and plasma frequency on the one hand and, on the other hand, lasers wave number and rippled density wave number lead to significant absorbed energy comparing to the non-resonance schematic. Cross-focusing of two lasers among the plasma changes the absorption of energy distribution across the plasma and, as a consequence, of this redistribution, spatial emission pattern of THz changes based on this pattern. The present paper discussion is divided into two main parts, In the first part, the interaction under the Rayleigh length has been investigated. In this part, it has been shown that the density of absorbed energy and THz emission are in complete agreement and in the other part, it has been discussed that the interaction in the resonance regime over the Rayleigh length has no significant consistency with the emitted THz radiation. It was revealed that the emission pattern of the THz in resonance schematic is the function of the absorbed energy under the Rayleigh length and in the lengths over the Rayleigh limit mismatching of laser wave vector and rippled density wave number leads to semi-resonance emission. The position of semi-resonance emission is under the influence of three parameters: i) absorbed energy of plasma, ii) mismatching of laser wave vector and rippled density wave number and iii) phase mismatching of radiation across the plasma.

The abnormal ring formation during the course of filamentation in laser-plasma interaction

The paper presents the ring formation during the course of filamentation in laser and weak inhomogeneous plasma interaction. Due to the combined influence of off-axial component and plasma density ripple, normal single ring changed into abnormal splitted ring during the course of filamentation. With increase in off-axial component and plasma density ripple, the abnormal splitted ring became stronger.

Beat wave cyclotron heating of rippled density plasma

AbstractLaser beat wave heating of magnetized plasma via electron cyclotron damping is proposed and analyzed. A plasma density ripple is presumed to exist across the magnetic field. Two collinear lasers propagating along the magnetic field exert a beat frequency ponderomotive force on electrons, driving a large amplitude Bernstein quasi-mode which suffers cyclotron damping on electrons. Finite Larmor radius effects play an important role in the heating. Electron temperature initially rises linearly with time. As the temperature rises cyclotron damping becomes stronger and temperature rises rapidly. The process, however, requires ripple wavelength shorter than the wavelength of the beat wave.

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.

Effects of the evolution of two cross‐focused Gaussian laser beams on the terahertz generation in thermal collisional plasma

Generation of the terahertz (THz) radiation based on the beating of two cross‐focused high intensity Gaussian laser beams in a warm rippled density plasma is numerically investigated, taking into account the ponderomotive force, Ohmic heating, and collisional nonlinearities. The beat ponderomotive force as a result of cross‐focusing of beams induces a vertical velocity component that by coupling with the rippled density gives rise to a nonlinear current deriving THz radiation. The effect of laser beams spot size evolution and plasma parameters on the THz generation is studied. It was found that there exist special electron temperature and laser intensity ranges with “turning points” where the generation of THz radiation reaches its maximum value and outside of these ranges, it disappears. The results also indicated that increasing the background electron density as well as taking into account the collision frequency help THz generation. Moreover, the maximum yield of THz radiation occurs when the beat wave frequency approaches the plasma frequency.

Influence of density ripple on pulse slippage of third harmonic generation in plasma

Influence of density ripple on pulse slippage of third harmonic generation has been investigated. When highly intense short range laser pulse incident on plasma, it imparts oscillatory velocity to electrons and exert a ponderomotive force at twice the frequency of incident laser beam. It induces oscillatory velocity at second harmonic frequency 2ω which further couples with density ripple resulting in density oscillations at 2ω. Density oscillations at 2ω, couple with the oscillatory velocity at ω, to produce non-linear current density at 3ω which drives the third harmonic generation. In order to provide phase matching condition between fundamental and third harmonic pulses, density ripple in plasma is introduced which offers the required momentum to the third harmonic photon to make the process resonant. At resonance, amplitude of the third harmonic pulse is found to be maximum for optimized values of density ripple factor. It is observed that the peak value of third harmonic pulse shifted towards higher value of normalized distance z' for higher values of normalized time t'. It is also seen that on account of the group velocity mismatch between pump and third harmonic pulses, the third harmonic pulse slips out of the domain of pump pulse.

Relativistic effects on propagation of q-Gaussian laser beam in a rippled density plasma: Application of higher order corrections

AbstractA nonparaxial investigation for propagation characteristics of q-Gaussian laser beam in rippled density plasma is studied by considering the relativistic nonlinearity. The field distribution in the medium is expressed in terms of q parameter and beam width parameter f. Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying approximation is solved in a modulated density profile. Analytical theory of self-focusing including higher order terms in the expansion of dielectric function up to fourth order is developed and the variation of beam width parameter f with the distance of propagation for different parameters is studied. One may note that increased value of density ripple, laser intensity and depth of modulation, increases self-focusing whereas a lower value of q shows strong self-focusing. A comparative study between paraxial and nonparaxial study has also conducted. This study is useful for research in high energy density physics.

Enhanced THz radiation generation by photo-mixing of tophat lasers in rippled density plasma with a planar magnetostatic wiggler and s-parameter

In this paper, the effects of planar magnetostatic wiggler and s-parameter on the terahertz (THz) radiation generation through rippled plasma have been investigated. Efficient THz radiation generation by photo-mixing of tophat lasers for rippled density plasma in the presence of the wiggler field has been presented. Fundamental equations for the analysis of the non-linear current density and THz radiation generation by wiggler magnetostatic field have been derived. It is shown that for the higher order of the tophat lasers, the values of THz amplitude are greater. In fact, the higher order of the tophat lasers has a sharp gradient in the intensity of lasers, which leads to a stronger nonlinear ponderomotive force and, consequently, a stronger current density. In addition, it is seen that by increasing s-parameter, the normalized transverse profile becomes more focused near the axis of y. Furthermore, it is observed that the normalized laser efficiency has a decreasing trend with increasing normalized THz frequency for different values of the wiggler field. Also, it is shown that by employing a greater order of the tophat lasers and a stronger wiggler field, the efficiency of order of 30% can be achieved. Moreover, it is found that we can control focus and intensity of THz radiation emitted in rippled plasma by choosing the appropriate order of the tophat lasers and tuning of the wiggler field.

High power terahertz radiation generation by optical rectification of a shaped pulse laser in axially magnetized plasma

An analytical expression has been derived for terahertz (THz) emission by optical rectification of a laser pulse having a Gaussian as well as hyperbolic-secant shape in axially magnetised ripple density plasma. The interaction between short laser pulses of sub picoseconds duration and plasma leads to the radiation of a wave having frequency in THz regime. The non-uniform intensity profile, say supper-Gaussian, of laser beam exerts a quasi-static ponderomotive force to the electron. The electron acquired a nonlinear transverse drift velocity component. Hence, a strong transient current density having a frequency component in the THz regime produces due to coupling of this velocity component with ripple density plasma and derives a strong THz wave. The generated THz field amplitude is directly proportional to the amplitude of the density ripple and field amplitude of the laser beam. In this generation mechanism, the ripple wave number plays a critical role. The THz field amplitude is maximized when cyclotron frequency approaches to the THz frequency and higher value of profile index. For typical laser plasma parameter, the emitted normalised amplitude of THz field is on the order of 10−2.

Terahertz radiation generation in magnetized plasma under relativistic effect

We have carried out analytical calculations for the emission of Terahertz (THz) radiation in the magnetized and rippled density plasma by beating of two high intensity cosh-Gaussian laser beams, which are capable of creating a relativistic effect in electrons' motion. We find the expression for the THz field achieved during the relativistic laser plasma interaction and study the effect of density of ripples, laser beam width, and magnetic field on the THz field. The role of skewness parameters of the lasers is also discussed in detail for efficient THz radiation.