Takashi Katagiri, Takahiro Suzuki, Yuji Matsuura,
https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-57/issue-5/054104/Time-domain-terahertz-gas-spectroscopy-using-hollow-optical-fiber-gas/10.1117/1.OE.57.5.054104.short
For gas analysis systems based on terahertz
time-domain spectroscopy (THz-TDS), relatively complex systems have been
proposed to enhance the sensitivity to measure small amounts of gas. This paper
proposes a simple system comprising a hollow optical fiber with an inner
dielectric layer as a low-volume and long-path gas cell THz-TDS-based gas
analysis system. The inner dielectric layer of the fiber not only reduces the
transmission loss for THz waves, but also protects the metal layer of the fiber
from reactive gases. The proposed dielectric-loaded fiber is fabricated by
depositing a metal thin film on a polymer film tube. In a gas analysis
experiment conducted using the fiber with a THz-TDS system, separating the
absorption peaks of NH3 gas and water
vapor initially proved to be difficult, although NH3 gas was successfully detected. However, by
improving the frequency resolution via Fourier transform and introducing a
longer hollow optical fiber, the two peaks were successfully separated and the
system sensitivity improved.
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