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Propagation of an electromagnetic (EM) pulse in an underdense plasma can either generate a wakefield or excite soliton wave, which depends on the competition between the linear dispersion and nonlinear self-modulation of the wave. Here, we study the interaction of the EM pulse and relativistic hot plasma analytically and numerically and reveal the physical mechanism of the transition from wakefield generation to soliton excitation in terms of soliton stability and modulation instability (MI) of a plane wave. Starting from the relativistic hot fluid-Maxwell model, a nonlinear Schrödinger equation (NLSE) governing the amplitude of scalar potential is obtained by using a multi-scale perturbation technique. The bright and dark soliton solutions of the NLSE are obtained analytically. The stability phase diagram of solitons is given numerically. Furthermore, the MI of the plane wave is studied, and the stability phase diagram of MI is obtained. The results indicate that, when the plasma density increases, the propagation of the EM pulse in the plasma experiences wakefield–soliton transition, which depends on the thermal effect. Our results provide theoretical evidence for deep understanding of high-power laser plasma interaction. [ABSTRACT FROM AUTHOR]

We study the propagation of a relativistic ultrashort laser pulse in two-dimensional inhomogeneous plasma with a density ripple based on the theoretical analysis and the particle-in-cell simulation. An analytical solution of the laser pulse propagating in the homogeneous plasma is completely obtained. It is found that the stable propagation of the relativistic ultrashort laser pulse in homogeneous plasma can be realized, and the propagation distance and intensity of the laser pulse and the spatial distribution of electron density can be effectively modulated by adjusting the pulsewidth of the incident laser and the plasma frequency. More interestingly, in the inhomogeneous plasma with a density ripple, when the wave amplitude of the density ripple is less than a critical value, the intensity of the ultrashort laser pulse is almost unchanged and the propagation characteristics of the laser in the inhomogeneous plasma are basically consistent with those in the homogeneous plasma. However, when the wave amplitude of the density ripple is larger than the critical value, the inhomogeneity of the plasma has an obvious effect on the laser characteristics, and the intensity and the spatial distribution of the laser pulse will be modulated by the plasma density ripple. The influence of the laser pulsewidth, plasma density, and plasma density ripple on the laser characteristics is discussed in detail. [ABSTRACT FROM AUTHOR]