Terahertz spectroscopy - occupying the electromagnetic band from roughly 0.1 to 10 THz, between microwave and mid-infrared - has long promised more than the laboratory could deliver. The physics is compelling: THz pulses transmit through polymer packaging, tablet coatings, and composite layers in ways that near-infrared and Raman cannot, and the technique is simultaneously sensitive to physical microstructure (porosity, density, crystal packing) and to low-frequency intermolecular vibrational modes inaccessible to conventional spectroscopy. The engineering challenge has always been translating that laboratory promise into hardware robust enough for industrial environments.

The 2025-2026 literature suggests that translation is under way across several sectors simultaneously. This roundup surveys the most substantive papers from that period, covering pharmaceutical PAT, battery and semiconductor manufacturing, food safety inspection, AI-enhanced chemometrics, and portable environmental sensing.

Pharmaceutical manufacturing: the Zeitler group’s in-line demonstrations

The most systematic body of 2025-2026 work in pharma comes from J. Axel Zeitler’s group at Cambridge, producing consecutive papers that push THz-TDS from bench characterization toward production-line integration.

The first, in the International Journal of Pharmaceutics, reported an in-line THz-TDS reflection system mounted on a lab-scale tablet press (DOI: 10.1016/j.ijpharm.2025.126273). The system measured tablet thickness (RMSEP = 0.013 mm), mass (0.63 mg), porosity (0.36%), breaking force (13.3 N), and disintegration time (3.5 s) simultaneously from a single pulse at approximately 1.5 seconds per tablet - five critical quality attributes from one non-contact measurement. A companion paper in Chemical Engineering Science addressed throughput, describing an automated spinning sample holder that catches, presents, and releases tablets at 50 Hz acquisition rates, permitting sub-second single-pulse capture at continuous manufacturing line speeds (DOI: 10.1016/j.ces.2025.121992).

Physical stability monitoring appeared in a third paper from the group, this one in the International Journal of Pharmaceutics in 2026. Leung and co-workers tracked 41 individual salbutamol amorphous solid dispersion tablets non-destructively over 15 months using THz-TDS, confirming absence of the 0.98 THz salbutamol phonon mode as a calibration-free crystallinity indicator - no sample preparation, no destruction, the same tablets measured repeatedly (DOI: 10.1016/j.ijpharm.2026.126903). The approach addresses a practical gap in stability programs for amorphous formulations, where conventional methods consume material and cannot track individual units longitudinally.

A fourth paper in Molecular Pharmaceutics (DOI: 10.1021/acs.molpharmaceut.5c00590) used temperature- and humidity-dependent THz-TDS to characterize how absorbed water plasticizes PVP/VA excipient polymer, reducing glass transition temperature from 367 K dry to 275 K at 75% relative humidity. The two distinct water-binding states identified were not detectable by differential scanning calorimetry alone - a result relevant to moisture specification-setting for amorphous solid dispersions.

Taken together, this cluster moves the Zeitler group’s THz work firmly into the territory that recent PAT validation literature has been mapping: simultaneous physical and chemical characterization from a single non-contact sensor, with demonstrated compatibility with ICH Q2(R2) real-time release frameworks.

Battery and semiconductor manufacturing

Outside pharma, the fastest-growing application area is high-throughput industrial metrology where contact-based methods are either too slow or too destructive.

For lithium-ion battery electrode inspection, Gao and co-workers at Nanjing University published a fiber-optic THz-TDS approach for lithium iron phosphate electrode quality control in Sensors (DOI: 10.3390/s25133917). A hybrid Savitzky-Golay and sinc-wavelet processing algorithm improved signal-to-noise ratio by more than 30%, expanding the detectable coating thickness range from 60-350 µm to 35-425 µm while reducing per-measurement time from 3 minutes to 5 seconds. At EV battery production rates, that throughput improvement is the difference between a laboratory reference check and an in-line system.

For semiconductor fabrication, Samsung Electronics researchers reported integration of near-field THz microprobes into a memory production line, achieving sub-10 µm spatial resolution for non-contact tungsten film conductivity measurement on individual memory cell patterns (Communications Engineering, 2025; DOI: 10.1038/s44172-025-00356-y). Agreement with four-point probe destructive reference yielded R² of 0.90-0.98 after signal correction. The authors characterize this as the first production-scale THz-TDS integration for semiconductor process monitoring.

Food safety and agricultural inspection

THz has a structural advantage in food inspection: it penetrates packaging without ionizing radiation, detects foreign bodies, and is sensitive to water content through strong hydrogen-bond absorption. A comprehensive review in Foods (DOI: 10.3390/foods14132199) covers pesticide residue detection, antibiotic identification, pathogen screening, adulteration, and moisture monitoring, noting that water’s dominant THz absorption is simultaneously a complication for high-moisture samples and a window into hydrogen-bond network dynamics.

Practical demonstration came from Lee and co-workers, who built a preprocessing algorithm for a 0.2 THz real-time conveyor imaging system that improved signal-to-noise ratio by an average of 6.0 dB and reduced Frechet inception distance by 16.7%, enabling metal and plastic foreign body detection without per-run calibration (PLOS ONE, 2025; DOI: 10.1371/journal.pone.0319978). Agricultural inspection is following the same trajectory: a deep-learning-enhanced THz imaging system for sprouted wheat achieved 97.5% classification accuracy at 13.6 ms inference per image (Plant Methods, 2025; DOI: 10.1186/s13007-025-01393-6).

AI integration has become the default analytical pipeline

The clearest cross-domain pattern in 2025-2026 THz literature is that standalone spectral fingerprinting is now the exception. A THz-TDS system combining plasmonic nanoantenna detectors with 4.5 THz bandwidth and a neural network classifier achieved 99.42% pixel-level classification across eight chemical species, and 88.83% accuracy for materials concealed under opaque paper (arXiv:2512.04330). In food adulteration work, variable selection methods - CARS, VCPA, LASSO - have become standard preprocessing steps for quantitative THz chemometric models. This convergence mirrors the broader move toward deep learning in spectroscopic process analytics, where the spectral data volume makes manual feature selection impractical.

Portable and airborne environmental sensing

Two papers from a group at the University of Rome describe, first, a portable THz-TDS prototype characterizing dichloromethane and chloroform (very short-lived ozone-depleting substances) in multi-component atmospheric mixtures alongside acetone and methanol (arXiv:2505.23956), and second, a UAV-mounted continuous-wave THz spectrometer for spatially resolved real-time atmospheric pollutant monitoring (Environment International, 2025; DOI: 10.1016/j.envint.2025.109819). The airborne paper extends THz process sensing from factory-floor installations to mobile outdoor emission monitoring - a scope expansion that would have been instrument-weight-limited five years ago.

The regulatory gap that still needs closing

No FDA or ICH guidance specific to THz spectroscopy as a PAT tool exists as of mid-2026. The applicable validation framework is ICH Q2(R2) and Q14 (both finalized 2024), which address chemometric and spectroscopic analytical procedures broadly. The Zeitler group papers reference these documents explicitly when framing real-time release architectures. As adoption broadens beyond specialized pharma laboratories into battery lines and semiconductor fabs, a technology-specific addendum to ICH Q14 implementation guidance would reduce the validation burden that each manufacturer currently builds from scratch.

The 2025-2026 literature has done what prior THz literature often failed to do: moved from optical curiosity to engineering result. The pharmaceutical and battery papers in particular report production-compatible throughput alongside analytically useful accuracy. The outstanding work is less about demonstrating that THz can measure something and more about building the chemometric infrastructure and regulatory acceptance criteria that let it do so at scale.