On the electromagnetic field energy in an isotropic transparent nonlinear medium

Expressions for the energy density of an electromagnetic field in an isotropic transparent medium with cubic or higher order nonlinearity are derived. For comparatively long pulses, the local energy density is shown to depend not only on the squared modulus of the electromagnetic field envelope but also on the ellipticity of polarization of the radiation at the same point. (c) 2004 MAIK "Nauka/Interperiodica".