Holographic Measurement of Surface Topography: Limits and New Options

Holograms offer a vast realm for optical 3D metrology. Even more so with the progress of digital holography: After digital storage of a complex wave-field, any kind of post-processing can be performed, any optical instrument (already invented or not yet invented) can be mimicked. A view over the fence: Processing of complex radio-signals allows for satellite 3D-radar with cm resolution, for 1000 km large radio telescopes - and black hole "imaging" by (IR) aperture synthesis. Whatever 'computational-optics' has in-store, it is the physical signal arriving at the camera-chip that will determine and fundamentally limit the final outcome. We discuss the origin of the ultimate uncertainty limits for holographic methods. Physics suggests that there are similarities to non-holographic concepts, but due to the virtually unlimited post processing options, we can sidestep some technical limitations. Even established sensors can be improved via 'holography+computation' and novel sensor concepts become possible, such as imaging hidden objects around corners and through scattering media. G. Häusler, F. Willomitzer, Light: Advanced Manufacturing 3, Article number 5 (2022)