  The two-point correlation function in thin films is studied near the critical
point of the corresponding bulk system. Based on fieldtheoretic renormalization
group theory the dependences of this correlation function on the lateral
momentum, the two distances normal to the free surfaces, temperature, and film
thickness are determined. The corresponding scattering cross section of X-rays
and neutrons under grazing incidence is calculated. It reveals the various
singularities of the two-point correlation function.
