Abstract
A theory previously used for computing the amplitude of light waves reflected and scattered from a rough surface in the medium where the light beam is incident is shown to be also applicable to the other medium. Furthermore it can be extended to approximations higher than the first order. As an example the formulae used in ellipsometry of very thin films are found. The amplitude of waves excited by a periodical surface structure in any direction is determined as well as its second order effect on both reflected and transmitted light. Computations are made for an arbitrary polarisation and an arbitrary incidence of the beam. Mean amplitude surface waves are considered in the case of high spatial frequency.