High-Sensitivity TDLAS Sensors Based on Double-Helix United/Split Spot Patterns.

This paper presents a highly sensitive tunable diode laser absorption spectroscopy (TDLAS) sensor based on a double-helix united/split spot pattern. A dense double-helix united spot pattern was designed based on a three-mirror multipass cell (MPC) to obtain high detection sensitivity in a compact structure. The corresponding minimum detection limit (MDL) for methane (CH) detection was enhanced to be 122.9 ppb. When the integration time was extended to 200 s, the MDL was reduced to 15.4 ppb. An example of a CH measurement application in urban environmental monitoring was presented in this research. A double-helix split spot pattern was designed to realize a real-time simultaneous dual-component TDLAS sensor. In the simultaneous and continuous monitoring of CH and acetylene (CH), a highly sensitive linear relationship with the concentration was successfully obtained. Corresponding MDLs for the CH/CH detection were calculated to be 354.7 and 111.2 ppb, respectively. When the integration time was set to 100 s, the corresponding MDLs were enhanced to 35.7 and 19.5 ppb, respectively.