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Nanoscale optical measurements with quantum optics and other techniques

Completed EMPIR project Light-matter interplay for optical metrology beyond the classical spatial resolution limits (17FUN01, BeCOMe) developed new optical measurement techniques for the investigation of structures at the nanoscale, with traceable spatial resolution beyond classical limits and sub-nanometre accuracy. This is important because high technology sectors such as semiconductors, software, biotechnology and computer electronics are increasingly working at the nanoscale, and traditional optics-based measurement systems cannot achieve the spatial resolution required. New techniques therefore needed to be developed to overcome current limitations.

Highlights of the project include:

• Metamaterial-based superlenses were design and fabrication during the project
• The consortium worked on solving inverse scattering problems by the development of novel methods which could provide better insights into the mechanism beyond the super-resolution
• Multiple far-field illumination far-field detection methods were developed by partners
• Collaboration between the project partners was strengthened by staff exchange during a Research mobility grant (RMG)
• Partners exploited invariant topological structures in electromagnetic fields
• Project explored the link between the near-field and far-field optical methods
• Project has established tip-enhanced Raman spectroscopy (TERS) using a sharp metal or metal-coated tip as a sensitive and enabling technique for nanoscale surface chemical characterisation
• The project explored the potential of quantum metrology in optical systems
• In order to support user uptake, the open-source software linked to the Finite-Difference Time-Domain (FDTD) calculations performed during the project has been made publicly available.

More detail of these highlights:

During the project, the consortium designed and fabricated metamaterial-based superlenses, which were developed in order to boost the spatial resolution of existing optical systems, such as optical scatterometers and microscopes, in the visible range of the electromagnetic spectrum. Five different designs of metamaterials-based superlens artefacts for novel far-field illumination far-field detection super-resolving optical metrology systems were developed.

The consortium developed far-field illumination far-field detection methods which included Hyperspectral Coherent Fourier Scatterometer (HCFS), Solid Immersion Lens (SIL)-based far-field illumination far-field detection, improved Deep Ultraviolet (DUV) setups, enhanced Alternative Gracing Incidence Dark (AGID) field microscopy and Substrate-enhanced label free bright field microscopy.

The collaboration between the project partners was strengthened by staff exchange from a Research mobility grant (RMG) between DFM (Danish National metrology institute) and VSL (Dutch National metrology institute). During the RMG, research on the metrological potential of Fourier scatterometry using small sphere lenses was performed and the resolution enhancement using half sphere over no sphere was demonstrated. The work of the RMG demonstrated that an enhanced scatterometry system with a sub-micrometer sized beam width was able to measure local variations beyond the limits of current optical technologies.

In addition, the project used different approaches to explore the link between the near-field and far-field optical methods. The different approaches included (i) the application of plasmonic lenses, (ii) the creation of subwavelength structured illumination using the fractional Talbot effect and (iii) resonance enhancement either by quasi-bound states in the continuum or by LSPR (localised surface plasmon resonance). As a result, the concepts for the characterisation of the form of nanostructures using polarisation information were investigated as well as far-field sensing concepts for sub-wavelength sized nanostructures based on support structures.

The project also explored the potential of quantum metrology in optical systems through spatial modes entanglement and its integration into existing optical systems. The project applied the sub-shot noise quantum technologies to optical systems, and built a new OPO (Optical parametric oscillator) system for generating squeezing in high-order modes and investigated the potential of quantum metrology optical schemes.

The project results were disseminated via 47 scientific open access publications and over 70 conference presentations.

Project Coordinator Lauryna Siaudinyte from VSL said

‘This project united the best nanometrology experts in Europe and demonstrated how joint effort can create a significant impact on the state-of-the-art. We are very happy with the high impact of the project, results presented in 47 scientific publications and over 70 conference presentations as well as continuation of our work in the sequel EMPIR project POLight.’

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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