Double-enhanced multipass cell-based wavelength modulation spectroscopy CH sensor for ecological applications.

A novel CH sensor based on wavelength modulation spectroscopy with a multipass cell was developed for the soil respiration measurement of CH. A home-made double-enhanced Herriot-type multipass cell with an effective absorption length of 73.926 m and a fiber-coupled distributed feedback diode laser emission at 1653.74 nm were used to design the sensor. The double enhancement of the effective optical pathlength of the multipass cell, absorption line locking, laser intensity normalization, and temperature control of the multipass cell were used to improve cell performance and achieve a minimum detection limit of 10 ppbv and a measurement precision of 6.4 ppbv. Finally, the potential of the developed CH sensor for ecological applications was verified by measuring the soil respiration of CH and monitoring of CH in the atmosphere over a long period.