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<p>Terahertz time-domain spectroscopy (THz-TDS) can underestimate the <i>Q</i> factor of high-<i>Q</i> metasurfaces fabricated on optically thick substrates, because time-windowing suppresses Fabry–Pérot (FP) echoes at the cost of spectral resolution. We present a quartz-calibrated THz-TDS workflow for echo-consistent comparison between experiment and full-wave simulation. Instead of removing substrate echoes from the measured waveform, we incorporate a calibrated finite-thickness quartz substrate into the simulation, so that ungated experimental spectra and simulated spectra are evaluated under matched physical conditions. The workflow is validated using bare quartz substrates, a MoS<sub>2</sub>-on-quartz sample, and multiple metasurfaces. For the thin-film case, the extracted parameters are fed back into full-wave simulations, and the resulting spectra reproduce both the transmission magnitude and the FP interference features. These results support the internal consistency of the analytical thin-film treatment and indicate that the extracted parameters capture the main spectral features under the present measurement conditions. For the metasurface case, a systematic gate-end-time analysis shows that the extracted <i>Q</i> factor is window-dependent for narrow q-BIC resonances, and the ungated echo-consistent spectra yield <i>Q</i> factors that agree more closely with the simulations.</p>

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Echo-consistent THz-TDS of Quartz-supported Structures: Thin-film Validation and Improved Q-factor Extraction for Metasurfaces

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Liqi Cui,
  • Jiangkun Tian,
  • Hongtu Li,
  • Guozhong Zhao

摘要

Terahertz time-domain spectroscopy (THz-TDS) can underestimate the Q factor of high-Q metasurfaces fabricated on optically thick substrates, because time-windowing suppresses Fabry–Pérot (FP) echoes at the cost of spectral resolution. We present a quartz-calibrated THz-TDS workflow for echo-consistent comparison between experiment and full-wave simulation. Instead of removing substrate echoes from the measured waveform, we incorporate a calibrated finite-thickness quartz substrate into the simulation, so that ungated experimental spectra and simulated spectra are evaluated under matched physical conditions. The workflow is validated using bare quartz substrates, a MoS2-on-quartz sample, and multiple metasurfaces. For the thin-film case, the extracted parameters are fed back into full-wave simulations, and the resulting spectra reproduce both the transmission magnitude and the FP interference features. These results support the internal consistency of the analytical thin-film treatment and indicate that the extracted parameters capture the main spectral features under the present measurement conditions. For the metasurface case, a systematic gate-end-time analysis shows that the extracted Q factor is window-dependent for narrow q-BIC resonances, and the ungated echo-consistent spectra yield Q factors that agree more closely with the simulations.