Figure 124

Fig. 124: The working principle of a quaternary Fresnel zone-plate: A Fresnel zone plate (FZP) consists of concentric rings designed so that the incident radiation is modulated in amplitude and/or in phase in order to interfere constructively along the optical axis at a point that represents the lens focus. In multilevel phase-shift FZPs, diffraction is performed primarily by phase modulation. Over a period, the optical path of the incident radiation increases by and the phase by 2. For each zone level, an appropriate thickness of the refractive material (phase-shifter) is then added to the different X-ray optical paths to correct this phase difference.