The four-quadrant phase-mask coronagraph. II. Simulations

In the first paper in this series, we described the principle of a coronagr aph utilizing a four-quadrant phase mask and the results of numerical simul ations obtained in the perfect case. In this second paper, we performed add itional numerical simulations to assess in more detail the performances and limitations of this coronagraph under real conditions. The effect of geome trical parameters such as shape and size of both the phase mask and the Lyo t stop is studied. We also analyze the effect of low- and high-order aberra tions generated, for instance, by the atmospheric turbulence. An important issue is the wavelength dependence of the phase mask. We show that the perf ormance decreases rapidly as the spectral bandwidth is increased, and as a consequence, we discuss the manufacturing of achromatized masks using multi ple thin films. An optical concept is proposed.