Fast monochromatic reflection nanoscopy by absorption modulation

• Applicant: Professor Dr. Alexander Egner
• Subject Area: Measurement Systems ; Coating and Surface Technology ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412938415

In many areas of materials science, the quantification of relevant parameters of technical materials is of central importance. Reflection optical microscopy is usually used for this purpose, since it requires little effort for sample preparation and is cost-effective. However, due to the diffraction-limited resolution of optical microscopes, more demanding methods, such as scanning electron microscopy, have to be used for modern materials with grain sizes well below one micrometer. Within the scope of a preliminary project funded by the DFG, which ran for about 18 months, we were able to demonstrate for the first time, to our knowledge, that the diffraction limit in optical reflection microscopy can be circumvented by using the principle of absorbance modulation. For this purpose, reversible apertures were imprinted into a photochromic layer (AML, absorbance modulation layer) which was deposited on the surface to be measured, thereby spatially constricting the reflecting region. The results of this preliminary work, which has already led to a joint conference contribution with our partners from the NanoVidere consortium, show that two-dimensional reflection measurements should be feasible in the future with an at least 5-fold resolution increase and image acquisition times within the same order of magnitude as for fluorescence nanoscopy. However, this requires further development of both the AML as well as the imaging process, as on the one hand, the increase in resolution has so far only been achieved in a line scan due to the low photostability of the AML used and, on the other hand, the imaging speed has been significantly lower than in diffractionlimited reflection microscopy. This subproject therefore aims to explore the principles for accelerating monochromatic absorbance modulation imaging (AMI) in reflection and to demonstrate a 5-fold resolution increase in two dimensions as compared to the diffraction limit. Within this context, the research focuses on the acquisition speed, in particular on the dynamics of the photophysical processes during image acquisition and the maximization of the detected signal, with special consideration of the photostability of the AML. Therefore, the reflection nanoscope which has been realized in cooperation with the Rembe research group in the scope of the preliminary project has to be improved and suitable measurement protocols have to be developed. This will be done in close cooperation with the Rembe group and includes the enhancement of our current simulation model. The work of the Egner and the Rembe groups (AMI group) will be closely connected with the work of the other partners of the consortium (Schmidt, Adams and Hell/Belov (AML group)). The AMI group will review the AMLs developed by the AML group with respect to their suitability for their respective subproject and utilize them for the development of hyperspectral (Rembe group) or fast monochromatic (Egner group) AMI reflection nanoscopy.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Claudia Geisler