Fig. 3

(a) Received signals measured during a spectral scan created via a current ramp, measured in laboratory air using a pathlength of approximately 5 cm, and a nominally 5776 nm (1731 cm⁻¹) QCL. The calculated absorbance (b) shows the presence of a water absorption line, confirmed to be at 5765.6 nm (1734.4 cm⁻¹), as expected using the current and temperature tuning parameters of Fig. 2.