V. I. Kirsanov

Nonlinear depletion of ultrashort and relativistically strong laser pulses in an underdense plasma

The depletion of a relativistically strong laser pulse in the course of interaction with underdense plasmas is considered. The driving mechanisms of distortion and fast depletion of the pulse due to the nonlinear plasma wake excitation are discussed. The role of the backward stimulated Raman scattering in the process of the leading front steepening is traced. Electron acceleration and heating due to plasma wave breaking are demonstrated. The evidence that the final stage of the pulse depletion can be accompanied by the formation of relativistically strong solitonlike electromagnetic modes is presented.

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...

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.

Stationary shock-front of a relativistically strong electromagnetic radiation in an underdense plasma

The propagation of a relativistically strong electromagnetic pulse in an underdense homogeneous plasma is considered with the focus on the possible existence of stationary structure of a pulse front. The analytical stationary shock-like solutions are obtained and analyzed. These solutions correspond to the conversion of the pulse electromagnetic energy to an electron plasma wave in the narrow region of the considered stationary front. Our theoretical analysis is supported by the PIC simulations, which demonstrate the formation and existence of the shock-like structure of the pulse leading front and extremely fast pulse depletion.

Stimulated scattering of relativistically strong radiation from an underdense plasma at high-frequency harmonics

The theory of stimulated scattering of relativistically strong, arbitrarily polarized laser radiation from an underdense plasma is developed. It is shown that, in addition to the scattering at the near-carrier frequency, the scattering at the odd and even high-frequency harmonics can occur in a wide range of angles. The growth rates of the instability associated with the harmonic generation are obtained as functions of the scattering angle. It is shown that, at certain directions, the growth rates for higher harmonics can exceed the growth rate for the fundamental harmonic.

Excitation of ultra-relativistic Langmuir waves by electromagnetic pulses

Excitation of ultra-relativistic Langmuir waves by short laser pulses has been considered. The possibility of electron acceleration in the longitudinal field is discussed.

Self-modulation of high-intensity laser pulses in underlense plasmas and plasma channels

The analysis is carried out for the basic regimes of the self-modulational instability of high-intensity (I∼1017−1018 W/cm2) laser pulses in underdense (ω0≫ωp) plasmas. The conditions under which these basic regimes dominate, growth rates corresponding to these regimes, and phase velocity of the plasma wave excited due to the instability are discussed in relation to the previous and possible future experiments on laser acceleration of electrons in the configuration utilizing the self-modulation of laser pulses.

Radial structure of the wakefield excited during the self-modulation of a laser pulse in a plasma

A study is made of the structure of the wakefield excited in the linear stage of the self-modulation of a high-power laser pulse in a homogeneous underdense plasma. It is shown that the fronts of the wake wave are curved and the profile of the wakefield amplitude differs strongly from the intensity profile of the laser pulse. The diffraction effects are found to play a key role in the formation of the transverse profile of the wakefield.

Self‐modulation of short intense laser pulse: Opportunities for wake‐field accelerator

Comparative analytical and numerical study of the laser pulse self‐modulation and the plasma wake‐field excitation is introduced for the cases when the self‐modulation is triggered by the relativistic self‐focusing and when it is initiated by the second frequency‐shifted weak‐intensity laser pulse. Both cases of a homogeneous plasma and a preformed plasma channel are considered. Basing on the obtained results, the new scheme of stimulation (by a second weak‐intensity laser pulse) and maintaining (using a preformed plasma channel) of the strong wake‐field excitation is proposed. This scheme gives an opportunity to provide enhanced acceleration at the distances of tens of the Reyleigh lengths and to obtain gigaelectronvolt energy of the accelerated electrons using the present‐day laser technology.