Mid‐infrared dissolved CO₂ measurement system using the ultra‐compact multipass cell

Abstract

To measure natural gas hydrate, a mid-infrared dissolved CO 2 measurement system is designed using the tunable diode laser spectroscopy with ultracompact multipass cell. The QCL laser of 4319 nm has a scanning range from 2315.05 to 2315.40 cm −1 , which contains 12 CO 2 and 13 CO 2 for isotope measurement and wide range of concentration detection. The optimized 3f + 1f wavelength modulation method reduces the limit of detection to 7.1 ppbv. An ultra-compact multi-pass cell with effective optical path length of 6.3 m and small volume of 15 ml is designed to achieve the system response time of 40 s. The dissolved CO 2 sensing system has been used in deep sea natural gas hydrate detection.

Ppb‐level CO2 sensor based on a miniature multipass cell with eight‐petaled spot pattern

“…34,35 Multipass cells compact a lengthy absorption path into a smaller physical space, thereby reducing overall system size. 36 John U. White, in 1942, introduced White cells, composed of three concave mirrors, resulting in a multipass structural design.…”

“…TDLAS technology, grounded in the Lambert–Beer law, asserts that extending the optical absorption path can substantially elevate detection sensitivity 34,35 . Multipass cells compact a lengthy absorption path into a smaller physical space, thereby reducing overall system size 36 . John U.…”