Femtosecond pulse propagation in air: Variational analysis

We use a variational method to study the phenomenon of intense femtosecond pulse propagation in air. This method allows us to obtain a semianalytical solution to the problem in which a wide range of initial conditions can be studied. In addition, it provides a simple physical interpertation, where t he problem is reduced to an analogous problem of a particle moving in a pot ential well. Different types of possible solutions are considered, with foc us upon the main physical interpretations. The results recapture at least q ualitatively some of the major experimental observations, and previous nume rical simulations.