An investigation of longitudinal intensity modulation of a relativistic laser beam in near-critical homogeneous plasma (n(e) > 1/4 n(cr)) is performed in this paper. On the basis of a nonlinear Schrodinger equation of electromagnetic vector potential, a model equation of the intensity profile is derived via the variational approach from Action and Lagrangian. Longitudinally uniform and longitudinally modulated pulse structures are viewed as different solutions of this model equation. For these two different types of pulse structure, their relative stability under different structure parameters is numerically studied. Numerical results indicate that this relative stability depends closely on the transverse structures of the laser pulse. (C) 2001 American Institute of Physics. [References: 26]
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