Resonant excitation of the upper hybrid wave by relativistic cross focusing of two laser beams

Abstract

This article presents the resonant excitation of the upper hybrid wave (UHW) by cross focusing of two high power laser beams in a collisionless hot magnetoplasma; taking into account the relativistic nonlinearity. The electric vectors of the two beams are polarized along uniform static magnetic field and the beams propagate perpendicular to the static magnetic field. The resonant excitation of the UHW occurs when the frequency difference (FD) of the two laser beams and difference of their propagation vector satisfy the dispersion relation corresponding to the UHW. It has been observed that the power associated with the excited UHW, which depends on the background electron concentration, magnetic field and the intensity of the two laser beams, becomes drastically modified with the distance of propagation. The effect of the excited UHW at the FD on the acceleration of electrons has also been discussed. The amplitude of the UHW, excited by two high power laser beams and the electron energy are also calculated. This study is relevant in heating of plasma near the upper hybrid frequency as well as electron acceleration. The results are presented for typical laser plasma parameters.

Excitation of an upper hybrid wave by two intense laser beams and particle acceleration

“…The UHW is excited due to nonlinear coupling by two ultrahigh power laser beams (because of relativistic and ponderomotive nonlinearities), which accelerate the electrons to high energies. The peak power of the UHW is reduced in comparison to the relativistic case [9]. This is on account of the fact that the ponderomotive force on electrons reduces the background electron density, therefore the amplitude of the upper hybrid wave reduced.…”

“…Excitation of an UHW has been the motivation for many experimental and theoretical studies because of their impact on the heating of plasma during inertial confinement fusion (ICF) and particle acceleration in which either self generated or external magnetic fields could be important [6][7][8][9][10]. Excitation of the UHW by cross focusing of two intense laser beams occurs if the difference frequency ( ω) and the difference of the propagation vector ( k) of the two laser beams satisfy the dispersion relation of the UHW.…”

“…Most of the earlier studies related to laser plasma interaction are limited to the cases where the electron nonlinearity due to relativistic mass variation or ponderomotive force take separately are accounted for cross focusing of two laser beams and beat wave process induced particle acceleration in unmagnetized/magnetized plasma [9,[24][25][26][27][28][29]. But in many situations the laser can create different type of nonlinearities at different time scales according to the inequalities (i) τ < τ pe or (ii) τ pe < τ < τ pi , hence one can have different time regimes.…”

Effect of mutual interaction of two cosh-Gaussian laser beams on upper hybrid wave excitation and subsequent electron acceleration

“…One of the most efficient methods for electron acceleration by UHW in laser plasma interaction is the beat wave acceleration scheme [7,8], where two intense laser beams of frequency difference (ω 1 and ω 2 ) equal to the plasma frequency (ω p0 ) excite the UHW resonantly. Through this scheme a large amplitude UHW can be generated by beating of two laser beams, which transfers its energy to plasma particles and accelerates the particles to higher energies [3,9,10]. In particular, particles injected into the beat wave region with a velocity equal to the phase velocity of the UHW gain more energy from the longitudinal electric field.…”

“…The excitation of UHW by intense laser beams has been extensively investigated in laser-plasma interactions [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. In these studies, various profiles of laser beam such as Gaussian, hollow Gaussian, q-Gaussian, Laguerre-Gaussian, etc have been used.…”