An innovative study published in Photonics Research, February 2025 (Vol. 13, No. 2) introduces a new terahertz imaging approach overcoming the diffraction limit by acquiring high-spatial-frequency components using a Fourier synthetic aperture.
This method enables:
- Subwavelength resolution beyond conventional THz imaging
- Hyperspectral imaging of complex and semi-transparent materials
- Time-resolved field-sensitive reconstruction for deeper insights into light-matter interactions
This study was conducted by Pitambar Mukherjee and Patrick Mounaix at the IMS Laboratory, Vivek Kumar, Lorenzo Valzania and Sylvain Gigan at the ‘Laboratoire Kastler Brossel’ (ENS – LKB), and Amaury Badon at the Photonics, Numerical and Nanosciences Laboratory (LP2N).
The project is funded by ANR (ANR-22-CE42-0005-HYPSTER, ANR 22-PEEL-0003-Comptera).
Detail:
https://doi.org/10.1364/PRJ.544076 (IF: 7,6)
Vivek Kumar, Pitambar Mukherjee, Lorenzo Valzania, Amaury Badon, Patrick Mounaix, and Sylvain Gigan, “Fourier synthetic-aperture-based time-resolved terahertz imaging,” Photon. Res. 13, 407-416 (2025)
Abstract:
Terahertz (THz) microscopy has attracted attention owing to distinctive characteristics of the THz frequency region, particularly non-ionizing photon energy, spectral fingerprint, and transparency to most nonpolar materials. Nevertheless, the well-known Rayleigh diffraction limit imposed on THz waves commonly constrains the resultant imaging resolution to values beyond the millimeter scale, consequently limiting the applicability in numerous emerging applications for chemical sensing and complex media imaging. In this theoretical and numerical work, we address this challenge by introducing, to our knowledge, a new imaging approach based on acquiring high-spatial frequencies by adapting the Fourier synthetic aperture approach to the THz spectral range, thus surpassing the diffraction-limited resolution. Our methodology combines multi-angle THz pulsed illumination with time-resolved field measurements, as enabled by the state-of-the-art time-domain spectroscopy technique. We demonstrate the potential of the approach for hyperspectral THz imaging of semi-transparent samples and show that the technique can reconstruct spatial and temporal features of complex inhomogeneous samples with subwavelength resolution.
Hyperspectral imaging for material characterization. (a) Schematic of the 100 μm thick imaging object composed of Teflon, Topas, and HDPE, showing the spatial distribution of the refractive index at 1 THz. (b) Distorted spatial variation in the refractive index profile at 0.5, 1, and 1.5 THz recorded using a diffraction-limited imaging system. (c) Reconstructed spatial refractive index profiles at 0.5, 1, and 1.5 THz illustrating the high-resolution material selectivity. (d) Variation in the refractive index of Teflon, Topas, and HDPE as a function of frequency rep-resenting comparison in the reconstructed refractive indices (solid lines) and material refractive indices (dashed lines). The 10 mm × 10 mm object illumination area is spatially sampled at 50 μm resolution, corresponding to 200 × 200 pixels.
