Abstract

A rarefied gas of neutral atoms cooled and trapped by means of the resonance light pressure forces’ is an example of a system when n λ3 ≤ 1, but Nα ≥¹. Here N denotes the density of atoms, λ is the light wavelength, a is the microscopic polarizability. It means that local field effects are essential, whereas Lorentz–Lorenz relation between α and refractive index n already, generally speaking, is not applicable. For rarefied gas even the question of the method integral equation² applicability in itself is not evident, but in any case its application implies that the Lorentz’s sphere radius must be much larger than wavelength, which is incompatible with the traditional approach. With the choice of a large Lorentz sphere the variables substitution method³ allowed to calculate simultaneously linear and nonlinear medium characteristics and to obtain a connection between local and macroscopic fields when the spatial dispersion is taken into account. These characteristics essentially depend on the interaction law between the particles. In the no-interaction condition (ideal gas) Lorentz-Lorenz formula is valid for arbitrary densities, including the case Nλ3<< 1. It has been revealed that for repulsive forces between the atoms in a case Nα ≥ 1 an effect of the optical transparency (n2− 1 << 1) takes place.

© 1993 Optical Society of America