C. J. McKinstrie

Transverse modulational instability of collinear waves

The transverse modulational instability, or filamentation, of two collinear waves is investigated, using a coupled nonlinear Schrodinger-equation model. For infinite media it is shown that the presence of the second laser field increases the growth rate of the instability and decreases the scale length of the most unstable filaments. Systems of two copropagating waves are shown to be convectively unstable and systems of two counterpropagating waves are shown to be absolutely unstable, even when the ratio of backward- to forward-wave intensity is small. For two counterpropagating waves in finite media, the threshold intensities for the absolute instability depend only weakly on the ratio of wave intensities. The general theory is applied to the pondermotive filamentation of two light waves in homogeneous plasma.

Effects of precompensation and postcompensation on timing jitter in dispersion-managed systems.

We present an analytic theory of timing jitter in dispersion-managed light-wave systems that is based on the moment method and the assumption of a chirped Gaussian pulse. We apply the theory to a soliton system and show that 50% postcompensation of the accumulated dispersion can reduce the jitter by a factor of 2. We also apply the theory to a low-power light-wave system employing the return-to-zero format and find that timing jitter can be minimized along the fiber link for an optimal choice of precompensation and postcompensation.

Two‐dimensional analysis of the power transfer between crossed laser beams

The power transfer between crossed laser beams made possible by an ion‐acoustic wave is studied. A simple formula is derived for the steady‐state power transfer, which depends on two dimensionless parameters: the ratio of the incident beam intensities and the normalized beamwidth. Numerical simulations show that the transient power transfer is larger than the steady‐state power transfer and usually oscillates in time. The convective depletion of the higher‐frequency beam saturates the power transfer more quickly than the damping of the ion‐acoustic wave.

Gordon–Haus timing jitter in dispersion-managed systems with lumped amplification: analytical approach

We use the moment method to calculate the Gordon–Haus timing jitter of optical pulses in dispersion-managed communication systems designed by use of lumped fiber amplifiers. The use of the Gaussian approximation for the chirped pulses, in combination with variational analysis, allows us to obtain an analytic expression for the timing jitter that is valid for an arbitrary number of amplifiers within each map period. We use this result to discuss how jitter is affected when more than one amplifier is used within each map period. We consider jitter for soliton-based systems as well as for low-power light-wave systems designed by use of the chirped return-to-zero format. In each case, the effects of dispersion compensation on the timing jitter are studied in detail.

Accurate formulas for the Landau damping rates of electrostatic waves

Systematic perturbation methods are used to derive formulas for the Landau damping rates of electron-plasma and ion-acoustic waves. These formulas are more accurate than the standard formulas found in textbooks.

Angular dependence of stimulated Brillouin scattering in homogeneous plasma

The angular dependence of stimulated Brillouin scattering (SBS) in a finite homogeneous plasma is studied. For parameters typical of inertial confinement fusion experiments, the initial evolution of SBS is well approximated by a one‐dimensional model. In the context of this linear model, the threshold intensity of the absolute instability and the steady‐state spatial growth rate of the convective instability are both independent of the scattering angle. However, the saturation time of the convective instability exhibits a strong inverse dependence on the scattering angle: Forward SBS always occurs in the transient regime and the intensity of the scattered light is less than that predicted by a steady‐state analysis. In particular, no light is emitted in the propagation direction of the incident wave.

Particle-in-cell simulations of ponderomotive particle acceleration in a plasma

In previous publications [C. J. McKinstrie and E. A. Startsev, Phys. Rev. E 54, R1070 (1996); 56, 2130 (1997)] the ponderomotive acceleration of electrons by an idealized (one-dimensional) circularly polarized laser pulse in a plasma was studied analytically. Acceleration gradients of order 100 GeV/m were predicted. To verify the predictions of the theoretical model, a two-dimensional relativistic particle-in-cell code was developed. Simulations of the interaction of a preaccelerated electron bunch with a realistic (two-dimensional) laser pulse in a plasma are presented and analyzed. The simulation results validate the theoretical model and show that significant ponderomotive acceleration is possible.

Electromagnetic instability and emission from counterpropagating Langmuir waves

This paper analyzes fundamental electromagnetic (em) emission, near the plasma frequency, from a pair of counterpropagating Langmuir pump waves in an externally driven plasma. The emission is a result of parametric instabilities of both Stokes (frequency‐downshifted) and anti‐Stokes (frequency‐upshifted) em waves. A new, sixth‐order dispersion relation is derived for the linearly unstable em waves. Previous treatments of this problem neglected the existence of two independent density ‘‘gratings’’ produced by the beating together of high‐frequency waves. These gratings, which can be resonant ion‐acoustic waves, are of comparable importance, and must be considered together in order to give the correct growth rates. The present results may have relevance to fundamental emission from laser‐driven targets and to other systems, such as the radio‐wave‐modified ionosphere.

Transverse instabilities of two intersecting laser beams in a nonlinear Kerr medium

We develop a detailed theory of the transverse instabilities that can occur as two laser beams intersect in a nonlinear Kerr medium. Our analysis of the interaction includes all the various sources of nonlinear phase shifts of the interacting fields as well as the mutual interaction of the two pump waves. In general, the interaction gives rise to a four-sidemode process. The couplings among the sidemodes arise from three distinct interactions of modulational instability, two-beam-excited (TBE) conical emission, and nonlinear Bragg diffraction. Modulational instability and TBE conical emission are shown to exhibit exponential spatial gain. The value of this gain is higher for the case in which both processes contribute than in the cases in which the two processes occur singly. Nonlinear Bragg diffraction is shown to be a spatially stable process by itself. However, in the presence of the other two processes this process provides an additional nonlinear phase shift that changes the direction of maximum growth of the instability. In none of the cases does the maximum growth occur for perfect linear phase matching.

Sound waves in two-ion plasmas

The dispersive and nonlinear characteristics of sound waves in plasmas that consist of warm electron and two different ion fluids are studied in detail. Analytical solutions are used to illustrate the characteristics of sound waves and to validate a numerical scheme that solves fluid and Poisson equations. This scheme can be used to model sound waves that participate in stimulated Brillouin scattering in two-ion plasmas.