Hyperspectral reflection nanoscopy via absorbance modulation

• Applicant: Professor Dr.-Ing. Christian Rembe
• Subject Area: Measurement Systems
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412988268

Modern materials have excellent strength and elasticity, which are achieved, for example, for metals by their small grain sizes (areas with the same microstructure) far below one micrometer and the chemical compositions. Due to the resolution of optical microscopes, which is limited by diffraction, light microscopic microstructure investigations, which are considerably less complex and less expensive than e.g. investigations using scanning electron microscopy (SEM), are no longer possible. The aim of the method projected here is to enable light microscopic spectroscopy of composite material surfaces with a resolution of a few tens of nanometers in the future. The working groups of the NanoVidere consortium want to use the principle underlying high-resolution far-field fluorescence microscopy (e.g. REversible Saturable OpticaL (Fluorescence) Transitions RESOL(F)T microscopy) to optically investigate surfaces with nanoscale resolution. For this purpose, the sample has to be covered with a thin photochromic layer, which can be switched intransparent by an activating laser at a first wavelength for a measuring laser at a second wavelength. By means of the ring-shaped mode (doughnut) of the activation laser beam known from RESOLFT, an aperture can then be created for the investigating measuring laser beam. The laser beam can then only illuminate the sample through this aperture, which means that only signals from this central area contribute to the imaging. The surface is scanned as with RESOLFT microscopy. In this subproject, the aim is to investigate whether hyperspectral nanoscopy can be realized with a thin absorbance modulation layer (AML) and broadband measuring light, with minimum and ideal targets based on the specifications in the requirements catologue (see the preamble of the project). Thus, in the NanoVidere project, AG Rembe aims to prove the following scientific hypotheses: • With a suitable two-dimensional scanning and thus imaging reflected-light nanoscope, AML can be used to achieve lateral resolutions that are significantly a factor of 2 below the diffraction limit of a scanning reflected-light confocal microscope. • With the photochromic polymer layers, a programmable near-field aperture for broadband measuring light can be generated in interaction with the activation laser, so that various optical measurement techniques such as spectroscopy can be performed in a scanning manner with a lateral resolution far below the diffraction limit. • With the help of a simulation model extended in relation to the previous work and comparative experiments, the physical processes involved in hyperspectral imaging can be understood in depth, so that the optimization of the method improves the informative value of the measurement data.

• DFG Programme: Research Grants