Speaker
Description
Mid-infrared (mid-IR) light, with its unique ability to probe vibrational, rotational, and electronic transitions, serves as a crucial tool for exploring fundamental light-matter interactions. Focusing electromagnetic radiation with enhanced energy density into extremely small sub-wavelength and nanoscale spatial regions is a cornerstone challenge in modern optics. This capability is essential for two key purposes: (1) probing emergent phenomena in materials through advanced imaging and spectroscopy techniques, and (2) enabling localized manipulation of the processes governing interactions among electrons, spins, and the lattice in materials.
Here, we present a state-of-the-art scanning probe instrument, High performance Wide spectral range Nanoprobe (HiWiN), featuring a campanile-shaped diamond tetragonal pyramid, to focus mid-IR light (wavelength l =10 μm) to a sub-wavelength spatial resolution of 1 μm using adiabatic compression of light. We fabricated a metal-insulator-metal (MIM) "campanile" (resembling a shape of the Italian "campanile" bell towers) pyramid and conducted 3D finite difference time domain (FDTD) simulations using Lumerical software to model a diamond based campanile probe as sketched in Fig.1a. To optimize the geometry for enhanced mid-IR focusing at the apex, we systematically varied the apex dimensions (along x and y axes) and the apex angle (θ).
The nanoprobe was attached to the LiNbO3 tuning fork that served as a detector of the mechanical pyramid apex-surface contact integrated in the Bruker Innova scanning probe microscope. We used this nanoprobe to measure the photovoltaic (PV) response in a Au-graphene-Au device using free electron laser operating at 10.5 µm. The simultaneously acquired topography and PV response maps are shown in the Fig. 2a. Horizontal line profiles, extracted from the center of the images, are plotted in Fig.5b, providing a direct comparison between the spatial variations in the device’s topography and its localized photovoltaic behavior. This nanoprobe enabled the detection of photovoltaic signals in a micro-structured graphene device, demonstrating its capability for sub-wavelength focusing of light with enhanced electric flux density for efficient localized manipulation and probing.
This advancement provides a powerful platform for investigating localized interactions, with significant potential for exploring quantum phenomena and advancing nanophotonic technologies in the unexplored mid-IR and THz spectral range.
Acknowledgements. We thank FELIX facility at Radboud University, Nijmegen, The Netherlands, for technical and organisational support and the UKRI Strategic Capital Equipment Grant EP/V00767X/1 and Lancaster University for financial support. The creative engineering support of Dutch Diamond Technologies and Bruker LTD was essential for the success of the HiWiN development.
The HiWiN instrument is now a user scanning probe facility at FELIX, open for cutting-edge research in physics and chemistry. It supports both far-field (mid-infrared through to terahertz) and near-field (mid-infrared with sub-micron spatial resolution) configurations https://hiwin-felix.org/.
