DIFFRACTION BY A SINUSOIDAL PHASE SCREEN

In order to develop computer simulations of diffraction patterns produ ced by scintillations, it is important to verify the simulations with examples of diffraction patterns that may be calculated analytically. One such example is classical knife-edge diffraction from a conducting half plane. Here we present another test case based on the one-dimens ional sinusoidal phase screen first considered by A. Hewish. Using Huy gens-Fresnel diffraction theory, we derive expressions, as a function of sinusoid scale size (Lambda) and maximum phase deviation (phi(0)), for (1) the intensity, (2) the horizontal wave number spectrum of the intensity pattern, and (3) the modulation index, seen by an observer s ituated below a one-dimensional phase screen with an incident plane wa ve. Then we compare the analytic results with a computer simulation. P rovided that the frequency resolution of the simulation is adequate, t he simulation agrees quite well with the analytic results, additionall y, diffraction from a sinusoidal phase screen provides a case in which the influence of increasing distance from the screen on the modulatio n index (deviation of intensity from its mean) may be explored analyti cally for both weak and strong scattering.