Harmonic generation by the propagation of two-colour laser beams in an underdense plasma

Abstract

An analytical theory is developed for studying the phenomenon of generation of efficient odd and even high harmonics by the propagation of two-colour linearly polarized laser beams in a homogeneous underdense plasma. The wave equation governing the evolution of the amplitude of various harmonics driven by the current density at corresponding frequencies is set up. The ratio of the fundamental frequencies of the two laser beams is considered to be an arbitrary integer. A numerical evaluation of amplitudes of the third, fourth and fifth harmonics has been presented. It is seen that the third harmonic amplitude generated by the two-colour system is enhanced in comparison to that obtained by a single laser beam. The detuning distance for the former is also increased in comparison to the latter case.

Phase-matched harmonic generation by two-colour laser beams propagating in plasma

“…However θ 1 cannot be increased beyond a certain cut-off value determined by the condition ε 1 = sin 2 θ 1 max θ 1 max = cos −1 ω p /ω , since the propagation constant k 1 becomes imaginary and the laser beam does not propagate. It is important to note that the phasematched third harmonic amplitude generated by the propagation of two-colour linearly p-polarized laser beams incident at appropriate unequal angles of incidence is two orders of magnitude larger than that obtained via normal incidence of two-colour laser beams for the same laser and plasma parameters [28]. The variation of the normalized third harmonic amplitude with propagation distance is shown in Figure 5, for the same parameters as in Figure 3.…”

“…Kfir et al [27] have experimentally generated bright, phase-matched, circularly polarized high harmonics by copropagating bichromatic driving laser beams in neon and cobalt gases. Recently, an analytical theory has been developed for studying the generation of efficient linearly polarized odd and even harmonics by the propagation of two-colour linearly polarized laser beams in plasma [28].…”

Second harmonic generation by propagation of a p-polarized obliquely incident laser beam in underdense plasma

“…1 This nonlinear interaction of laser pulses with plasma is relevant to a wide range of applications such as laserplasma based accelerators, 2,3 X-ray laser, 4,5 inertial confinement fusion, [6][7][8] and harmonic radiation generation. [9][10][11][12] Generation of harmonic radiation is an important subject of laser plasma interaction and attracts great attention due to a wide range of applications. The interaction of linearly polarized, intense laser beams with homogeneous plasma induces transverse nonlinear plasma currents, resulting in the generation of odd harmonics of the laser frequency in the forward direction.…”