The problem of absorption in the Fresnel fringe analysis

Fresnel fringes at interfaces of CoCu, FeTb and AuFe multilayers were simulated using a multislice algorithm in connection with a continuum model. The intensity profiles of a defocus series were calculated by treating the absorption in different ways. A first simulation uses absorption in the calculations. These simulated intensities were divided by the intensity of the in-focus image. This “division method” results in shapes of fringe intensities different from those of a second simulation using no absorption. This outcome is important because the division method is widely used to get rid of absorption in experimentally observed images. In a system like CoCu where the absorption difference between the individual materials is small there is no need for a division because the simulations with and without absorption are very similar.