Signal & Data Processing
Terahertz data processing begins before image reconstruction. Time-domain traces require reference measurements and temporal alignment; spectra require phase-aware calibration; FMCW beat signals require sweep correction and range processing. Low-frequency detector noise, coherent artefacts, saturation and multiple internal reflections can all propagate into the final image if they are not treated at the signal level.
The next stage is an inverse problem. Depending on the experiment, the unknown may be a refractive-index map, layer thickness, complex wavefront or three-dimensional attenuation distribution. The model must describe enough of the propagation physics to make the estimate meaningful, while remaining identifiable from the available measurements.
Segmentation and morphological analysis are applied only after this physical reconstruction. In one breast-tissue study, refractive-index thresholding combined with morphological dilation reported approximately 80% sensitivity and 82% specificity in the best tested configuration. In real-time tomography, segmentation, component labelling and skeletonization extracted structural metadata from reconstructed volumes. Both examples require their sample set, reference method and failure modes to remain visible in the editorial account.
Processing pipelines that transform time traces, spectra, radar signals, and image sequences into interpretable information.
Signal & Data Processing across the measurement chain
The workflow can include requirement definition, instrument selection or development, calibration, acquisition, signal processing, reconstruction, and interpretation. The first decision is rarely the choice of an instrument. It is the identification of the physical quantity that could answer the research question: an interface delay, a spectral feature, a complex refractive index, a local field component, a surface profile, or a volumetric morphology.
Once that quantity is defined, source bandwidth, detector architecture, numerical aperture, scan geometry, dynamic range, sample environment, and reference measurements can be considered together. This system-level approach is particularly important in the terahertz range, where propagation loss, diffraction, atmospheric absorption, coherent artefacts, and material dispersion may all influence the same dataset.
Calibration, interpretation and validation
A capability is meaningful only when its limits are explicit. Work therefore asks which contrast mechanism is physically interpretable, what bandwidth and geometry are required, how repeatability is measured, and which independent method can serve as a reference. Reconstruction may improve access to phase, depth, or morphology, but it does not remove the need to test model assumptions and uncertainty.
Related publications
- Linear to radial polarization conversion in the THz domain using a passive system — DOI
The work presents a compact, passive device that transforms a conventional linearly polarized terahertz (THz) beam into a radially polarized one, a field configuration that offers superior focusing, enhanced longitudinal fields, and improved coupling to near‑field probes. By adapting a proven optical mode‑selection technique to the THz regime, the authors employ a circular metallic waveguide that supports only the fundamental TE11 and the radially polarized TM01 modes. A discontinuous phase element placed at the waveguide entrance inverts the polarization over half the beam, converting…
- Theoretical and experimental studies of metallic grids absorption: Application to the design of a bolometer — DOI
The study delivers a comprehensive, validated framework for designing metallic grid absorbers with precisely tailored electrical resistivity, enabling the creation of efficient, room‑temperature bolometers and other thermal detectors. By treating structured metal layers as equivalent homogeneous films whose resistivity depends on geometry, the authors derived analytical expressions for transmission, reflection, and absorption that incorporate skin‑depth effects and diffraction when the grid period approaches the wavelength. Numerical simulations and experimental measurements at 0.3 THz and in the RF band confirm the model’s accuracy, demonstrating that…
- Near-field wire-based passive probe antenna for the selective detection of the longitudinal electric field at terahertz frequencies — DOI
The work presents a novel passive probe antenna that can be operated at terahertz (0.1 THz) frequencies using a simple, purely passive structure. The antenna consists of a slender metal wire backed by a discontinuous phase plate that converts an ordinary linearly‑polarized free‑space beam into a radially polarized guided mode on the wire, with an estimated coupling efficiency of about forty percent. By exploiting the Sommerfeld wave that travels along the wire, the device can create a highly confined, longitudinal electric field at the…
- Continuous‐wave scanning terahertz near‐field microscope — DOI
The work reported by Guillet, Chusseau, Adam, Grosjean, Penarier, Baida and Charraut describes the development of a continuous‑wave terahertz (THz) near‑field microscope that exploits Sommerfeld surface waves guided along metallic wires. By combining differential phase plates, a Y‑splitter and a sharp, tapered needle probe, the authors created an imaging system that can be coupled to any linearly polarized THz source and detector. The key achievement is the demonstration of sub‑micrometre‑scale resolution—roughly a third of the probe tip radius, or about 10 µm—while retaining sensitivity…
- A comprehensive study of the application of the EOP techniques on bipolar devices — DOI
The study demonstrates that Electro‑Optical Probing (EOP), a non‑invasive laser‑based diagnostic technique, can be reliably applied to bipolar semiconductor devices to uncover internal electrical activity and identify failure mechanisms that are otherwise invisible to conventional analysis. By measuring the modulation of a reflected 1350 nm laser beam on the backside of transistors, the researchers quantitatively correlated signal variations with the electric field, carrier distribution, and doping profiles within the base, emitter and collector regions. Experiments on both a reference NPN transistor array and a…