Broadband gas phase absorber detection and quantification by chirped laser dispersion spectroscopy at 1.55 µm

The demonstration and first evaluation of chirped laser dispersion spectroscopy (CLaDS) for quantitative measurements of gas molecules with broad spectral features is reported. The demonstration is conducted on propyne (methyl acetylene) gas, using a widely tunable external cavity near infrared laser, λ ≈ 1.55 µm, whose frequency can be swept at 2.6 MHz/µs. A direct baseband downconversion scheme is implemented to recover molecular dispersion, with a cost-effective 32 GHz radio frequency architecture. Laboratory tests demonstrate in particular the value of laser dispersion spectroscopy for the sensing of turbid media with a large range of variations, owing to a significant immunity of the detection scheme to variations in received optical power. Normalized minimum concentration measurable in the 1.5 ms scan is ∼0.7 ppm.m.√Hz.