Abstract.  Intense laser pulses while propagating through neutral gases ionize them. If the intensity of the laser is not sufficiently high, the gases may not be completely ionized, hence giving rise to partially stripped plasma. The propagation medium for a laser beam in partially stripped plasma consists of a linear and a nonlinear plasma current due to free electrons as well as linear and nonlinear polarization field due to bound atomic electrons. Polarization fields can arise from a number of processes [1-3], the dominant process being electronic polarization arising due to modification of the atomic electron distribution by the optical field. The polarization field due to atoms in partially striped plasma can be expressed as a power series of the electric field of the laser.

The present paper deals with the effect of nonlinear polarization field and plasma current density on the evolution characteristics of a laser pulse propagating in partially stripped plasma. The wave equation describing the laser field amplitude driven by plasma current density as well as polarization field of the bound atomic electrons is set up. Using a variational technique the equations governing the simultaneous evolution of the spot-size and length of a laser pulse propagating in partially stripped plasma are obtained and solved numerically.

References
[1] E. Esarey, P. Sprangle and J. Krall
Phys. Rev. E, 54, 4211 (1996).
[2] Y. R. Shen
The principles of nonlinear optics, Wiley, New York (1984).
[3] R. W. Boyd
Nonlinear optics, Academic, San Diego (1993).