Abstract
The HITRAN database (High-Resolution Transmission molecular absorption database) is an extremely helpful reference for selecting lines of molecular species. In the case of water vapor, a particular strong absorption line around λ ≈ 1392.5 nm is suitable for the detection of molecules, not only because of its high strength but also because it is well separated from the neighboring transitions, thus avoiding any overlap. First, we present the optical system that uses a distributed feedback (DFB) laser diode, emitting around λ ≈ 1392.5 nm with a power ≈ 3 mW and linewidth ≤ 10 MHz. For metrological needs, we are looking for a means to control the water vapor concentration in ambient air in near real time and especially when an optical chilled mirror hygrometer is used. The latter instrument is widely used due to its performance with regard to both accuracy and repeatability of measurements. Here, using the molecular absorption device the use of such an instrument is examined from the point of view of its impact on the measurement of relative humidity. This paper reports the measured frequency positions of the observed line at λ = 1392.5337 nm for different air pressures and compares them with the values given in the HITRAN database. In addition, we discuss the possibility of using water vapor detection by spectroscopy to observe the change of the shape and the position of the absorption line produced during measurements of the dew point temperature by the optical chilled mirror hygrometer.
Highlights
Water vapor concentration in air, often expressed as relative humidity, plays a key role in many fields including mass metrology
To justify the fact that one needs to control the variations of humidity whenever it is used, we evaluated the order of magnitude of the perturbation of the air humidity caused by water vapor condensation on the mirror of the instrument, during the measurement of the dew point temperature
It consists of a 5 mm diameter mirror, of high optical quality, with temperature controlled for dew point measurements
Summary
Water vapor concentration in air, often expressed as relative humidity, plays a key role in many fields including mass metrology. In this last scientific field, its value must be determined and controlled with great precision, during measurements of an unknown mass by comparison with a standard referenced in the International System of Units (SI) [1, 2]. We consider a water vapor detection device based on the absorption spectroscopy technique [5, 6], to highlight and discuss the degree of invasiveness of the condensation hygrometer. In the case of water vapor, a relatively intense isolated absorption line, centered around the wavelength of 1392.53 nm, is chosen to avoid any overlap with neighboring transitions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
