In order to obtain information about the internal structure of fluctuating Cooper pairs in the pseudogap state and below the transition temperature of high T<Subscript>c</Subscript> superconductors, we solve the Bethe-Salpeter equation for the two-electron propagator in order to calculate a “pair structure function” <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$g_{P}({\mathbf{P}},\pmb{\rho})$</EquationSource> </InlineEquation> that depends on the internal distance <InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\pmb{\rho}$</EquationSource> </InlineEquation> between the partners and on the center of mass momentum P of the pair. We use an attractive Hubbard model with a local potential for s-wave and a separable potential for d-wave symmetry. The amplitude of g<Subscript>P</Subscript> for small ρ depends on temperature, chemical potential and interaction symmetry, but the ρ dependence itself is rather insensitive to the interaction strength. Asymptotically g<Subscript>P</Subscript> decreases as an inverse power of ρ for weak coupling, but exponentially when a pseudogap develops for stronger interaction. Some possibilities of observing the pair structure experimentally are mentioned. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006
