Structured amplitude and phase fields behind microstructures: The quest for high contrast modulation at proximity
Microstructures can be used to realize repetitive and singular high contrast features at different distances behind a structure. For practical applications, the amplitude field needs to be considered. To realize defined amplitude features at long distances behind the surface of reference, the phase of the light field plays a crucial role. The highest contrast can be reached if phase singularities (or phase jumps) can be used because at the positions of their appearance in space the intensity becomes zero. In practice, it is important to identify cases where phase singularities can be designed in position in space. As a first example, we will discuss the case of phase fields produced by Talbot light carpets for wavelengthscale amplitude gratings. Such systems are used today in lithography to print small repetitive structures. For arbitrary structures to be printed, different design strategies are necessary. As a second example we will discuss the case of rule based design phase mask technique to realize high-resolution prints at proximity. In such a case phase singularities are created at the phase level and can be found still at long distances, which leads to high contrast modulation far behind the microstructure. An interesting situation appears when a fully optimized diffractive optical structure is used to create particular amplitude fields at defined proximity distances. We will discuss the appearance of phase singularities behind the structure in such a case and give details of their behavior at long proximity distances.