Preformed Plasma Channel Research Articles

Relativistic self-action of $$\:\varvec{q}$$-Gaussian laser pulses: impact of preformed parabolic plasma channels

Relativistic self-action of $$\:\varvec{q}$$-Gaussian laser pulses: impact of preformed parabolic plasma channels

Q-Gaussian laser beams in preformed parabolic plasma channels: effect of ohmic heating on self action effects

q-Gaussian laser beams in preformed parabolic plasma channels: effect of ohmic heating on self action effects

Direct laser acceleration: A model for the electron injection from the walls of a cylindrical guiding structure.

We use analytical methods and particle-in-cell simulation to investigate the origin of electrons accelerated by the process of direct laser acceleration driven by high-power laser pulses in preformed narrow cylindrical plasma channels. The simulation shows that the majority of accelerated electrons are originally located along the interface between the channel wall and the channel interior. The analytical model based on the electron hydrodynamics illustrates the underlying physical mechanism of the release of electrons from the channel wall when irradiated by an intense laser, the subsequent electron dynamics, and the corresponding evolution of the channel density profile. The quantitative predictions of the total charge of released electrons and the average electron density inside the channel are validated by comparison with the simulation results.

Resonant excitation of plasma waves in a plasma channel

We demonstrate resonant excitation of a plasma wave by a train of short laser pulses guided in a preformed plasma channel, for parameters relevant to a plasma-modulated plasma accelerator (P-MoPA). We show experimentally that a train of N≈10 short pulses, of total energy ∼1J, can be guided through 110mm long plasma channels with on-axis densities in the range 1017–1018cm−3. The spectrum of the transmitted train is found to be strongly red shifted when the plasma period is tuned to the intratrain pulse spacing. Numerical simulations are found to be in excellent agreement with the measurements and indicate that the resonantly excited plasma waves have an amplitude in the range 3–10GVm−1, corresponding to an accelerator stage energy gain of order 1GeV. Published by the American Physical Society 2024

Self action effects of q-Gaussian laser beam in preformed parabolic plasma channels: effect of nonlinear absorption

Self action effects of q-Gaussian laser beam in preformed parabolic plasma channels: effect of nonlinear absorption

Collective effect of preformed plasma channel and plasma density ramp on second harmonic generation of Laguerre–Gaussian laser beam in plasma

Collective effect of preformed plasma channel and plasma density ramp on second harmonic generation of Laguerre–Gaussian laser beam in plasma

Propagation dynamics of q-Gaussian laser beams in preformed collisionless plasma channel: self-focusing, self-channeling, and self-phase modulation

Propagation dynamics of q-Gaussian laser beams in preformed collisionless plasma channel: self-focusing, self-channeling, and self-phase modulation

Electron acceleration by wakefield generated by the propagation of chirped laser pulse in plasma

A study of generation of wakefield and particle acceleration via propagation of linearly polarised, chirped, Gaussian laser pulse in preformed plasma channel is presented. Perturbation technique is used to separate slow and fast varying plasma electron velocities and density. Considering the laser pulse length and amplitude to be evolving along the propagation distance, nonlinear fluid equations are used to derive longitudinal electric wakefields at varying propagation distances for chirped as well as unchirped pulses. It has been seen that longitudinal wakefield amplitude generated by positively (negatively) chirped laser pulses is higher (lower) than the amplitude obtained by unchirped laser pulses. The wakefield amplitudes are optimized with respect to the propagation distance. Further, trapping and acceleration of electrons by the generated wakes, is analysed. Comparing the energy of an accelerated test electron using chirped and unchirped laser pulses, it is shown that positively chirped laser pulses are capable of accelerating test electron to maximum energy using minimum injection energy. Hence, highest energy gain can be obtained by propagation of positively chirped laser pulse in plasma.

Laguerre–Gaussian laser beam guiding and its second harmonics in plasma having density ramp

This paper presents the optical guiding of a laser beam in plasma by using a preformed plasma channel. The density ramp in plasma density due to the plasma pressure has also been considered. The effect of ponderomotive force has been taken into account which originates due to the intensity gradient present in the laser beam. This force produces a plasma gradient by expelling plasma electrons from a high-field to a low-field region, providing heavy ions remain immobile. Plasma oscillations result from a gradient in plasma density that excites an electron plasma wave. The equation governing the plasma wave excitation has been found by using linear perturbation theory. An in-phase mixing of an incident laser beam with this plasma wave generates its second harmonics. Laguerre–Gaussian laser profile has been used for harmonic production. Moment theory has been used to obtain a differential equation for beam waist, which has been solved numerically by Runge–Kutta's fourth-order method. The effect of different modes of Laguerre–Gaussian profile, beam intensity, plasma density, channel depth, and slope of density ramp has been explored.

Excitation and enhancement of wakefield by beating of two laser beams in a preformed plasma channel: An analytical study

We investigate analytically the nonlinear interaction of two beating laser beams with plasma by considering electron density inhomogeneity in the axial and radial directions. We apply the fluid model coupled with Maxwell equations to obtain a nonlinear equation for studying the plasma wave. We solve this nonlinear equation using the hypergeometric and Airy functions and present the damping and outgoing wave solutions. Our results show that the longitudinal and transverse wakefields generated in the preformed density-ramped plasma channel are much stronger than the inhomogeneous plasma with density-ramped profile.

Guiding of Laguerre–Gaussian pulses in high-order plasma channels

In laser wakefield accelerators, guiding of drive laser pulses in preformed plasma channels plays a key role to overcome laser diffraction for effective acceleration. Different from guiding schemes studied previously, where a Gaussian laser pulse and a parabolic plasma channel were investigated, here we investigate the guiding of Laguerre–Gaussian (LG) pulses in plasma channels. Analytical studies and three-dimensional particle-in-cell simulations show that the matched conditions still exist for high order laser pulses and high order plasma channels. For usual Gaussian and high order LG pulses, the second order parabolic channel gives the best guiding. Although the laser pulse can also be guided in even higher order channels, its envelope deforms during propagation. For laser pulses with combined multi-LG modes, determined by their azimuthal orbit angular momenta, there is axisymmetric or non-axisymmetric evolution for the transverse laser intensity profile. The preformed plasma channel can guide the combined pulses but the transverse intensity profile of the laser pulses always evolves.

Discharge plasma formation in square capillary with gas supply channels

A comprehensive model of processes in a discharge capillary is required in order to obtain nominal parameters of a preformed plasma channel suitable for the laser wake-field acceleration. We present three-dimensional magnetohydrodynamics simulations of a hydrogen gas filling process and discharge plasma formation in a short square shaped capillary with gas supply channels. Time evolution of the gas pressure and the plasma density in the capillary channel for a chosen discharge current profile is analyzed. Performed simulations provide distributions of the electric current, the magnetic field, and the electron density along the whole channel, taking into account gas supply areas as well as areas outside of the capillary. Obtained results show that the presence of gas supplies leads to the inhomogeneous plasma density distribution along the capillary channel which has to be taken into account for generating an optimal laser-driven electron beam.

Experimental study on capillary discharge for laser plasma wake acceleration

Preformed plasma channels play important roles in many applications, such as laser wakefield acceleration, plasma lens, and so on. Laser pulses can be well guided when the radial density distribution of the plasma channel has a parabolic profile and it is matched with the laser focus. Discharging a gas-filled capillary is a possible way to form such plasma channels. In this work, we report the capillary discharging and laser guiding experiments performed in the Laboratory for Laser Plasmas at Shanghai Jiao Tong University. The plasma density distributions in the Helium-filled discharged capillary are measured by using the spectral broadening method. In a capillary with a length of 3 cm and a diameter of 300 μm, the plasma density profile is observed to be uniformly distributed along the axial direction and have a parabolic profile along the radial direction. Parameters for plasma channel generation are scanned. The deepest channel depth obtained is 28 μm, which is close to the focal spot radius of the laser used in the experiment. Laser guidance in the plasma channel is also studied. The results show that the laser can maintain its focus and continuously propagate when the channel depth matches the focal spot, indicating that the well guiding of the laser pulse by the preformed plasma channel is obtained. These studies may serve as the ground work for the future studies, such as staged laser wakefield acceleration and phase-locked wakefield acceleration.

Study of optical guiding of the Hermite–Gaussian laser beam in preformed collisional parabolic plasma channel and second harmonic generation

Abstract In the present work, the scheme of optical guiding of the Hermite–Gaussian laser beam and the generation of second-harmonic 2ω radiation (ω being the frequency of incident beam) is presented in plasma having the preformed collisional plasma channel in which density variation is parabolic. The nonlinear coupling of excited electron plasma wave with the carrier or incident beam results in the production of second harmonics of the latter. The method of moments is used for finding the coupled differential equations for the beam diameter to study the dynamics of the Hermite–Gaussian laser beam in plasma under the effect of the collisional parabolic channel. For numerical simulations, the Runge–Kutta fourth-order numerical method is used. Standard perturbation theory gives the equation for excitation of electron plasma wave which further acts as the source term for the second harmonic generation. The numerical results show that the preformed plasma channel has a significant effect on the guiding as well as on the 2ω generation of the Hermite–Gaussian laser beam in plasma.

Optical guiding of intense Hermite–Gaussian laser beam in preformed plasma channel and second harmonic generation

This work presents the scheme of optical channeling of the intense Hermite Gaussian laser beam and second-harmonic generation in plasma having the preformed plasma channel, where relativistic nonlinearity is operative. Excitation of the electron plasma wave at the incident beam frequency leads its coupling with the latter produces the second harmonics of the beam. For the formulation of differential equations for the beam waists of the Hermite Gaussian laser beam propagating through the channel, the method of moments has been used. The solutions of the coupled differential equations are found using Runge Kutta fourth-order numerical method. Perturbation theory has been applied to find the equation governing the excitation of electron plasma wave and hence the source term for the second-harmonic yield. It has been observed that the preformed plasma channel helps to optically guide the laser beam and enhances the efficiency of second-harmonic generation of various modes of the Hermite Gaussian laser beam in plasma.

Nonlinear propagation of an intense Laguerre–Gaussian laser pulse in a plasma channel* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61665006 and 61865011) and the Natural Science Foundation of Jiangxi Province of China (Grant Nos. 20171ACB21018, 20161BAB212041, and 20162BCB23012).

The nonlinear propagation of an intense Laguerre–Gaussian (LG) laser pulse in a parabolic preformed plasma channel is analyzed by means of the variational method. The evolution equation of the spot size is derived including the effects of relativistic self-focusing, preformed channel focusing, and ponderomotive self-channeling. The parametric conditions of the LG laser pulse and plasma channel for propagating with constant spot size, periodically focusing and defocusing oscillation, catastrophic focusing, and solitary waves are obtained. Compared with the laser pulse with fundamental Gaussian (FG) mode, it is found that the effect of vacuum diffraction is reduced by half and the effects of relativistic and wakefield focusing are decreased by a quarter due to the hollow transverse intensity profile of the LG laser pulse, while the effect of channel focusing is the same order of magnitude with that of the FG laser pulse. Thus, the matched condition for the intense LG laser pulse with constant spot size is released obviously, while the parameters of the laser and plasma for the existence of solitary waves nearly coincide with those of the FG laser pulse.

Nonlinear Evolution of q-Gaussian Laser Beams in Preformed Parabolic Plasma Channels

Theoretical investigation on nonlinear propagation characteristics of q-Gaussian laser beams in preformed parabolic plasma channels has been presented. The optical response of the channel has been modelled by ponderomotive nonlinearity. Following Virial theorem in W.K.B approximation, semi analytical solution of the wave equation for the field of laser beam has been obtained. Particularly the evolutions of beam width and axial phase of the laser beam have been investigated in detail. Self trapping of the laser beam arising as a consequence of the cancellation of diffraction broadening by nonlinear refraction of the laser beam has also been investigated.

A filter or oscillator by a simple density hump for an intense laser propagating in a preformed plasma channel

Considering the relativistic self-focusing, the ponderomotive self-channel, and the preformed channel focusing, the effect of a density hump on the laser propagation in a preformed plasma channel is studied. The evolution equation of the laser spot size is derived by using the source-dependent expansion technique. It is found that the laser behavior after the hump strongly depends on the hump position and width and is also related to the hump altitude. For the incident laser with a constant spot size, the laser after the hump may oscillate or not change, only depending on the hump width under a certain hump altitude. For the incident laser with oscillation, the laser oscillation can be enlarged, decreased, unchanged, according to the hump width, position, and altitude. So, the density hump can play the role like a filter, or like an oscillator, or be ineffective by adjusting its width, position, and altitude. These results are well confirmed by the final numerical simulations.

Multi-color, femtosecond [formula omitted]-ray pulse trains driven by comb-like electron beams

Photon engineering can be exploited to control the nonlinear evolution of the drive pulse in a laser–plasma accelerator (LPA), offering new avenues to tailor electron beam phase space on a femtosecond time scale. One promising option is to drive an LPA with an incoherent stack of two sub-Joule, multi-TW pulses of different colors. Slow self-compression of the bi-color optical driver delays electron dephasing, boosting electron beam energy without accumulation of a massive low-energy tail. The modest energy of the stack affords kHz-scale repetition rate at manageable laser average power. Propagating the stack in a pre-formed plasma channel induces periodic self-focusing in the trailing pulse, causing oscillations in the size of accelerating bucket. The resulting periodic injection generates, over a mm-scale distance, a train of GeV-scale electron bunches with 5D brightness exceeding 1017A∕m2. This unconventional comb-like beam, with femtosecond synchronization and controllable energy spacing of components, emits, via Thomson scattering, a train of highly collimated gigawatt γ-ray pulses. Each pulse, corresponding to a distinct energy band between 2.5 and 25 MeV, contains over 106 photons.

Effects of relativistic and channel focusing on q-Gaussian laser beam propagating in a preformed parabolic plasma channel

The propagation of q-Gaussian laser beam in a preformed plasma channel is investigated by means of the variational method. A differential equation for the spot size has been obtained by including the effects of relativistic self-focusing, ponderomotive self-channeling and preformed channel focusing. The propagation behaviors and their corresponding physical conditions are identified. The comparison of the propagation between q-Gaussian and Gaussian laser beams is done by theoretical and numerical analysis. It is shown that, in the same channel, the focusing power of q-Gaussian laser beam is lower than that of Gaussian laser beam, i.e., the q-Gaussian laser beam is easier to focus than Gaussian laser beam.