We address and solve a fidelity problem in Fourier-transform infrared nanospectroscopy (nano-FTIR). As the technique is increasingly adopted for characterizing composite materials and nanophotonic systems, the nanoscale nature of the measurements introduces new challenges: current hyperspectral image acquisition at high spatial resolution suffers from significant artifacts caused by thermal instabilities that affect tip/sample positioning, so for long acquisitions both the spatial and spectral fidelity become unreliable. To overcome this, we introduce a new nano-FTIR measurement methodology based on step-scan interferometry combined with image registration. We demonstrate that our approach delivers superior spatial fidelity for nano-FTIR experiments and enables the collection of larger, reliable datasets.

G. Németh, F. Borondics, Step-scan interferometry for high-fidelity hyperspectral nanoscopy, ACS Nano 11 xxxx−yyyy, (2026), DOI: xx.xxxx

We present a robust, freely accessible framework for scattering-type scanning near-field optical microscopy (s-SNOM) data analysis and modeling as an add-on to Quasar, addressing a key gap in the field. While the commercialization of s-SNOM instruments has made nanoscale imaging, spectroscopy, and hyperspectral measurements available to a broad community of laboratories, the data analysis tools have lagged behind, leaving researchers dependent on fragmented, hard-to-reproduce in-house codes. To democratize s-SNOM data analysis, we implemented flexible, experiment-specific processing pipelines together with numerical modeling capabilities in a graphical, visual programming environment for reproducible data analysis. By consolidating these capabilities in a single open-source platform, we aim to make s-SNOM data processing and interpretation more transparent, exchangeable, and reproducible across the growing near-field optics community.

G. Németh, M. Toplak, S. Read, R. Freitas, F. Borondics, Robust and Democratic s-SNOM Data Analysis and Modeling in Quasar, ACS Omega 11 32971−32980, (2026), DOI: 10.1021/acsomega.6c02534

Photocurrent is a critical observable in a wide range of physical processes across different length scales, serving as a valuable tool for the characterization of semiconductors or two-dimensional materials. Recently, photocurrent mapping, particularly when combined with magnetothermal transport effects, such as the anomalous Nernst effect (ANE), has been used to image magnetic domains and domain walls. To gain access to photocurrents on the nanoscale, this effect is combined with infrared scattering-type scanning n ear-field optical microscopy, in which strong field enhancement is created at the apex of an atomic force microscopy (AFM) tip, which serves as the confined illumination source creating localized temperature gradients through light absorption in the sample, which can be exploited for ANE detection. Herein, ANE photocurrents generated in a cobalt–iron–boron channel and the optical scattering are compared between various AFM tips, revealing significantly differing behavior for different tips. To gain insight into the origin of these differences, the measurements are further compared to finite element method simulations of tips with varied tip apex radii.

D. Dai, D. Siebenkotten, Z. Šobáň, A. Girnghuber, P. Krzysteczko, A. Hoehl, J. Wunderlich, B. Kästner, Photocurrent Nanoscopy in the Near Field: A Comparative Study of Different Atomic Force Microscopy Tips in Relation to Their Optical Performance, Physica Status Solidi A 222 2400736, (2024), DOI: 10.1002/pssa.202400736

We present a detailed investigation of the near-field optical response of core–shell nanoparticles using Fourier-demodulated full-wave simulations, revealing significant modifications to established contrast mechanisms in infrared scattering-type scanning near-field optical microscopy (s-SNOM). Our work examined the complex interplay of geometrical and optical resonances within core–shell structures. Using a finite element method (FEM) simulation closely aligned with the actual s-SNOM measurement processes, we capture the specific near-field responses in these nanostructures. Our findings show that core–shell nanoparticles exhibit unexpected distinct resonance shifts and massively enhanced scattering driven by both the core and shell properties. This investigation not only advances the understanding of near-field interactions in complex nanosystems but also provides a refined theoretical framework to accurately predict the optical signatures of nanostructures with internal heterogeneity.

D. Dai, R. Ciesielski, A. Hoehl, B. Kästner, D. Siebenkotten, Core–Shell Nanoparticle Resonances in Near-Field Microscopy Revealed by Fourier-Demodulated Full-Wave Simulations, Nano Letters 24 13747–13753, (2024), DOI: 10.1021/acs.nanolett.4c03940

We demonstrate that the asymmetric interferograms commonly observed in nano-FTIR are an intrinsic consequence of the measurement geometry rather than an instrumental imperfection. Because the sample is located within the interferometer, its frequency-dependent complex scattering coefficient introduces spectral phase shifts that break the symmetry of the interferogram around zero optical path difference, unlike in conventional FTIR. Through theoretical analysis, numerical simulations, and experimental measurements, we show that the degree of asymmetry is directly related to the sample's optical resonances and dispersion. We explain how this affects Fourier transformation, phase retrieval, apodization, and spectral reconstruction, highlighting that standard FTIR processing assumptions based on interferogram symmetry can introduce artifacts in nano-FTIR. Our paper establishes a theoretical framework for understanding asymmetric interferograms and provides practical guidance for improving the accuracy of nano-FTIR spectroscopy.

G. Németh, H. A. Bechtel, and Ferenc Borondics, Origins and consequences of asymmetric nano-FTIR interferograms, Optics Express 32 15280-15294, (2024), DOI: 10.1364/OE.520793