Development of a Portable Mid-IR Spectrometer for Simultaneous Measurements of Six Trace Gases in the Atmosphere

Commercial gas sensing is traditionally performed using Fourier-transform infrared (FTIR) or non-dispersive infrared (NDIR) spectroscopy. Advances in interband cascade laser (ICL) technology now enable the development of compact, affordable, multi-gas laser spectrometers suitable for both industrial and atmospheric monitoring. In this work we present a portable mid-IR absorption spectrometer built around a compact laser module from NanoPlus that integrates three ICLs. The design supports an additional three-laser module, enabling up to six measurement channels and positioning this platform as a practical alternative to conventional instruments for a wide range of applications. 

Figure 1. Custom FPGA-based hardware platform, allowing for simultaneous control of up to six laser diodes.

The instrument is fully controlled by a custom-built, FPGA-based hardware platform responsible for high-speed data acquisition and signal generation (Fig. 1). The electronics provide six high-resolution input and six output channels, all operating at clock rates of up to 50 MHz, enabling precise, low-latency control and measurement of the optical system. An additional modular analog amplifier stage provides flexible signal conditioning for optical detectors and laser drivers. The spectrometer measures 52.5 × 35 × 19.1 cm, weighs 20 kg, and consumes 63 W of electrical power with active heating. An integrated heater stabilizes the optical bench at 32 °C, improving long-term stability. The instrument achieves 1σ precision of 160 ppb for CO2 (40 s), 200 ppt for CH4 (30 s), 180 ppt for CO (60 s), 1 ppb for N2O (60 s), 2.2 ppm for H2O (30 s), and 60 ppb for CS2 (10 s). We quantify the benefits of thermal control and validate concentration retrievals against certified gas mixtures. Field tests include vehicle-mounted mobile survey, a multi-day stationary deployment, and industrial monitoring of hydrogen impurities. Across these applications, the spectrometer demonstrates reliable, calibration-free retrievals of ambient greenhouse gas concentrations at up to 10 Hz refresh rate.

Acknowledgements

This work is part of the “Hydrogen Region East Austria Goes Live (H2REAL)” project and is funded by the Austrian Climate and Energy Fund as part of the “Energy Model Region” program, which is managed by the Österreichische Forschungsförderungsgesellschaft FFG.