Fig. 21: Amplitude of the fundamental of the intensity distribution versus the reduced distance for a 2000 LPI grating (dots) and a 4000 LPI grating (squares) obtained at an X-ray wavelength of 0.69 Å. The Fourier coefficient was scaled for the maximum possible contrast, directly related to the thickness modulation of the grating. The fitted lines correspond to simple analytical expressions which include the effect of the degree of coherence at the position of the sample.