High-Temperature H2O Vapor Measurement Using Terahertz Spectroscopy for Industrial Furnace Applications

We verified that high-temperature (773 K) H
₂
O vapor can be measured quantitatively with terahertz (THz) spectroscopy in the frequency range of 0.5-0.8 THz. The linear relationships between the absorbance peak area and the H
₂
O vapor volume mixing ratio (VMR) at three absorption peaks (0.557 THz, 0.658 THz, and 0.752 THz) match HITRAN-based simulations closely, which indicates that the HITRAN database can be used for practical applications. Particularly, since the peak at 0.658 THz only appears at high temperatures, it can be used to measure high-temperature H
₂
O vapor directly in the presence of room-temperature ambient H
₂
O vapor.