L. M. Gorbunov

Stimulated processes and self‐modulation of a short intense laser pulse in the laser wake‐field accelerator

The basic equations for self‐consistent pulse evolution taking into account stimulated Raman backward and near‐backward scattering are formulated. These equations are used to study the three‐dimensional (3‐D) axisymmetrical self‐consistent laser pulse evolution analytically and numerically. Special attention is paid to the case of the pulse self‐modulation. The spectra and intensity of backscattered radiation are obtained in both the strong and weak coupling limits. A simple criterion to ignore the action of stimulated Raman backscattering on the pulse evolution is derived. The possibility of using a backscattered radiation spectrum for diagnostics of both the laser‐pulse and generated wake‐field evolution is discussed. Triggering of the laser‐pulse self‐modulation by the relativistic self‐focusing and by a second frequency‐shifted weak‐intensity laser pulse is discussed. Basing on the obtained results, a new configuration of stimulation and maintaining a strong wake‐field excitation is proposed. This con...

Structure of the wake field in plasma channels

An equation is derived that describes the linear response of an underdense inhomogeneous plasma [ω0≫ωp(r), where ω0 and ωp(r) are the laser-carrier and plasma frequencies, respectively] during the propagation of a laser pulse along the axis of a plasma channel with a characteristic width Rch. For a wide channel, i.e., when Rch/λp0>1 (where λp0=2πc/ωp0 is the wavelength of the excited plasma wave and ωp0 is the plasma frequency at the channel axis), the structure of the wake field is studied analytically. It is shown that this structure changes with the distance from the trailing edge of the pulse. As a result, at a certain distance behind the pulse, the fraction of the plasma wave period in which the simultaneous focusing and acceleration of electrons are possible increases by a factor of 2. For a narrow channel (Rch/λp0<1), the structure of the wake field is studied numerically and it is shown that, in this case, the doubling of the phase interval of the wave where the simultaneous focusing and accelerat...

Laser wakefield structure in a plasma column created in capillary tubes

The structure of the wakefield is studied in a plasma column, created by a monomode laser pulse propagating in a capillary tube, filled with gas affected by tunneling ionization. Linear analytical considerations as well as self-consistent numerical simulations show that in the central bulk part of a plasma column where the laser intensity exceeds the ionization threshold, the wakefield structure is similar to that of an infinite homogeneous plasma. Near the wall of the capillary tube, where the laser intensity decreases below the ionization threshold and where the plasma density falls to zero, the curvature of the plasma wave phase front increases with the distance from the laser pulse, resulting in small-scale radial electric field which may undergo phase mixing.

The theory of laser self-resonant wake field excitation

The three-dimensional evolution of a short laser pulse is considered. The linear stability analysis that takes account of the scattered light convection and predicts a development of pulse modulation at the electron plasma frequency, is carried out. It is demonstrated that a laser pulse with a power above or close to the critical, which is required to provide a pulse relativistic self-focusing, undergoes compression and self-modulation in the course of self-consistent pulse evolution and, as a result, resonant excitation of an extremely strong plasma wave occurs. It is shown that for a properly taken initial pulse and plasma parameters it is possible to obtain a wake field of an extremely high intensity for a fairly long time to provide a new promising outlook for the laser accelerator concept. The influence of plasma inhomogeneity and pulse initial focusing on the considered self-resonant plasma wave excitation is studied.

Dynamics of a plasma channel created by the wakefield of a short laser pulse

A new physical effect of a plasma channel formation by the ponderomotive force of a wakefield excited by a short laser pulse with duration of the order of electron plasma oscillation period ωp0−1 (ωp0 is the plasma frequency) is discussed. The hydrodynamic and particle numerical codes, including plasma ion response, are used to simulate the long-term wakefield behavior. It is found that the wakefield creates a channel with a radial profile depending on the laser pulse width. Particularly, for a narrow pulse, wherein the width is less than c/ωp0 (c is the speed of light), the channel has an annular form with on-axis density maximum. The depth of the channel increases with the distance from the pulse until fine-scale mixing arises and the wake starts to break. Particle simulations show that wave breaking results in emergence of fast electrons taking an essential part of the wake energy during a few plasma periods. Quasilinear fluid equations describing self-consistently, the laser wakefield generation, and ...

Filamentation of ultrashort laser pulses propagating in tenuous plasmas

The filamentation of ultrashort laser pulses (shorter than a plasma period) propagating in tenuous plasmas is studied. In this regime relativistic and ponderomotive nonlinearities tend to cancel each other. Time-dependent residual nonlinear plasma response brings about the dynamical filamentation with the maximum unstable transverse wave number decreasing in the course of laser pulse propagation. Dynamics of a hot spot that seeds the filamentation instability is studied numerically and reveals a good agreement with the analytical results.

Linear theory of resonance self-modulation of an intense laser pulse in homogeneous plasma and plasma channels

The analytical solutions describing the linear stage of the intense-laser-pulse self-modulation, which results in a strong plasma wakefield excitation, are studied in terms of the paraxial approximation. The attention is focused on phase relations that were ignored in the previous studies. It is shown that the value of the phase velocity of the plasma wake wave differs from the pulse group velocity so that under some specific conditions, the relativistic factor corresponding to the phase velocity can be substantially less than that for the group velocity. This may be important for the particle acceleration in the self-modulated laser wakefield accelerator.

Laser surface wakefield in a plasma column

The structure of the wakefield in a plasma column, produced by a short intense laser pulse, propagating through a gas affected by tunneling ionization is investigated. It is shown that besides the usual plasma waves in the bulk part of the plasma column [see Andreev et al., Phys. Plasmas 9, 3999 (2002)], the laser pulse also generates electromagnetic surface waves propagating along the column boundary. The length of the surface wake wave substantially exceeds the length of the plasma wake wave and its electromagnetic field extends far outside the plasma column.

Ion momentum driven by a short intense laser pulse in an underdense plasma

The analysis of a one-dimensional relativistic two-fluid hydrodynamical model shows that a short powerful laser pulse propagating in underdense plasmas generates an averaged momentum of plasma ions. Analytical results are in excellent agreement with numerical simulations performed with a particle code.

Parametric decay of an electromagnetic pump wave in a two-dimensionally inhomogeneous plasma

The decay instability of an ordinary hf electromagnetic pump wave into quasitransversal upper hybrid (UH) and lower hybrid (LH) waves in the ionosphere is discussed. The longitudinal and transversal inhomogeneity of the medium is taken into account. It is shown that, due to the decay instability within weak plasma density enhancements, a rather broad spectrum of UH oscillations, similar to the spectrum of the downshifted maximum (DM) in stimulated electromagnetic emission (SEE) spectra, is formed. Estimates of the frequency range and characteristic k numbers of the DM spectrum are given.