A new terahertz (THz) spectroscopy system addresses a long-standing measurement challenge by capturing high-resolution spectral data alongside near-field spatial detail. Developed by researchers at Tianjin University, China, the spatial-resolved asynchronous-sampling terahertz spectroscopy (SPRATS) system integrates asynchronous optical sampling (ASOPS) with a micrometer-scale photoconductive probe (PPB), enabling close-range characterization of THz resonant structures with minimal compromise in resolution.
THz spectroscopy plays an important role in the study of functional materials, waveguides, and chemical sensing. However, conventional setups have struggled to combine the fine frequency resolution needed to probe sharp resonances with the spatial resolution necessary for mapping near-field interactions. SPRATS overcomes this limitation by using ASOPS – where time delays are mapped via two offset lasers – to capture time-domain waveforms with 100 MHz spectral resolution, while the PPB provides spatial resolution down to 20 µm.
The team used the system to study a silicon dual-period grating exhibiting a leaked guided-mode resonance (GMR), a structure that selectively couples and leaks THz energy. In situ near-field mapping confirmed field localization and antisymmetric phase distributions predicted by simulation. The authors also reported improved far-field resonance measurements compared to a conventional THz time-domain system, attributing this to the small sampling area of the PPB, which helped isolate the signal from central device regions while reducing edge effects.
“Our SPRATS system demonstrates superior performance in spectral resolution and effectively extends the near-field research to the terahertz spectral modulation devices with high Q factor,” said co-author Jianqiang Gu in a press release.
According to the authors, the system could aid the development of narrow-line width filters, high-sensitivity THz sensors, and other components used in chemical detection, wireless communication, and nonlinear optics. It may also support deeper exploration of light-matter interactions at subwavelength scales – an important goal in terahertz photonics and materials research.
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