Wavelength-Selective and Order-Dependent Efficiency Behaviour of Deep 'Blaze-Like' Diffractive Multi-Order - Multi-Layer Structures: Design, Systematic and Process Modeling, and Experimental Validation – ‘Select’

• Applicant: Professor Dr. Robert Brunner
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538491566

The objective of the project ‘Select’ is the fundamental investigation of a generalisable model for Multi-Layer diffractive optical elements (MLDOEs) for simultaneous, tailored wavelength-selective efficiency distribution across multiple selected diffraction orders. So far, research on MLDOEs has almost exclusively focused on 'efficiency achromatisation,' i.e., the objective was limited to achieving high diffraction efficiency in only one diffraction order across a selected wavelength range. In this project, we are taking a significant step further and explore new opportunities and properties for imaging systems and significantly expand the capabilities of well-established systems. In detail, our focus lies on designing diffractive optical elements that distribute high diffraction efficiency wavelength-selectively, for example, among 0th, 1st, 2nd, and -1st orders, thus enabling distinct focal points for these orders by inducing either positive, negative, or no additional optical power for the DOE. In addition to theoretical (simulation) based studies, also experimental investigations are necessary to determine the manufacturability of the structural parameters. In order to attribute the diffraction efficiency to very different diffraction orders, ‘unusual’ materials such as high-index liquids, nanocomposites and layer materials with strong dispersion are particularly considered. Anticipated challenges for the fabrication of MLDOEs require the precise fabrication of blazed structures and therefore involve: large structure heights (ranging from 0.5 µm to > 50 µm), highly (‘optically’), smooth surfaces of blaze facets (roughness in the nanometre range), prevention/reduction of corner rounding, avoidance of periodic structuring artifacts, and notably, the feasibility of structuring a wide range of various materials. To meet these requirements with a high degree of flexibility, combined process series of laser grey-tone lithography and dry etching techniques (RIE/RIBE) are being investigated. A further central challenge in the fabrication of MLDOEs concerns the filling of surface profiles using materials with highly specific and often very different dispersion properties.

• DFG Programme: Research Grants