J. Eur. Opt. Society-Rapid Publ. 21, 7( 2025) 71
Figure 16. Intensity profile of the yellow arrow in image of the cross for STED mode( a) and confocal mode( b). The dotted lines in( b) show the border of the pattern based on the drop of intensity in STED mode.
Figure 17. Design of planned possible reference structures.
plasmonic scattering or other alternative detection channel switching schemes can be realized, so that pump-probe SRM schemes are not applicable, non-linear SIM methods will be the remaining options. The possible switch-able and non-linear detection schemes described in Section 3 appear to be quite universally applicable. In combination with( coherent or incoherent) Raman scattering, a chemical imaging can increase the imaging contrast and performance.
6 Conclusion and outlook
In this publication we presented an overview about research performed by several partners within a European research project on the way to realise universal label-free SRM methods suitable for reliable optical dimensional nanometrology as an imaging complement to well-proven non-imaging OCD methods and a fast and contamination free alternative to nano-imaging methods such as AFM or SEM, which are required to characterise individual and single structures and defects.
We provided a short review on the performance and applications of the investigated linear and non-linear SIM and novel pump-probe SRM techniques including surface plasmon resonances( SPR) assisted Raman, coherent multiphoton-Raman, and STED-like methods.
In this work, we have shown investigations of thoughfocus microscopy, a method to improve nanoscale sensitivity in classical microscopy by adding phase information to the analysis. Different novel schemes to apply SIM methods
have been investigated based e. g. on photon statistics evaluation and in a combination of structured illumination Raman and hyperspectral imaging( WISER), both showing quite promising results.
Additionally, we investigated the NV centres in different artificial diamond as a promising candidate for superresolution imaging due to its high fluorescence stability. Desired patterns were fabricated on an NV-centre substrate. By examining photoluminescence spectra, we found that NV centres in the substrate have a uniform distribution and sufficient spectral resolution. We imaged the fabricated pattern on the NV-centre substrate using both STED and confocal modes. We determined the optimum experimental parameters for imaging our sample with STED microscopy. Compared to confocal mode, STED mode provides better contrast at the borders of features and patterns. Therefore, STED mode is a promising tool for dimension measurement of nanostructures on substrates with NV centres. While an increase in STED power is often associated with improved resolution, our sample exhibited damage points at STED power levels above 5 %. Different values of STED power could be used to investigate this further by preparing an NV-centre substrate with smallersized patterns as well as compatible with a high power of the STED laser.
To go beyond super-resolution imaging and extend it to a quantitative dimensional metrology tool, as stated in the introduction, some requirements must be addressed.
Beside a stable and reproducible measurement system and a very good understanding of the probe-sample interaction, which usually comes along with a detailed, reliable and