Collapse behavior of laser beam in plasma

On the basis of the nonlinear equation for the wave packet of the elliptically polarized laser electric field, the Lagrange density function of the nonlinear equation is constructed by means of field theory. It is shown that the energy focus of the wave packet possesses the characteristic of quasi-particles. Moreover, the conserved quantities of plasmons, momentum, and energy are given. The collapse dynamics of the wave packet at the later stage of modulation instability is discussed. The normalized density distribution of the plasmon number is regarded as weight, and the wave packet of the laser electric field is analyzed. The result shows that the scale of the wave packet will collapse to a very small value in finite time, proving that the laser electric field possesses the collapsing be