Absolute concentration measurements of bacterial CO2 emission using a 2004 nm vertical cavity surface emitting tunable diode laser

This paper reports the use of tunable diode laser absorption spectroscopy to make absolute measurement of the concentration of carbon dioxide (CO<inf>2</inf>) emitted by E. coli and lactic acid bacteria (LAB) at different stages of their growth cycle. The emission wavelength of a 2004 nm vertical cavity surface emitting laser diode is scanned across the R16 rotation-vibration line of CO<inf>2</inf> at 2003.5 nm (4991.259 cm^-1) by current tuning. Direct detection is performed to recover the lineshape accurately and the absolute values of the CO<inf>2</inf> concentration are extracted over the growth cycle of the bacteria. The time-varying CO<inf>2</inf> emissions agree well with theoretical models available in the literature. The calibration-free nature of these measurements is particularly important for such experiments.