[Incoherent broadband cavity enhanced absorption spectroscopy based on LED].

High sensitivity incoherent broadband cavity enhanced absorption spectroscopy based on high power LED was developed. The detection sensitivity was demonstrated by measuring the absorption of NO2 over the wavelength range of 472. 3-479. 3 nm. A broadband incoherent light (emitting from high power LED peaked at 457 nm) was coupled to a 92.5 cm long high finesse optical cavity consisting of two 30 mm diameter plano-concave mirrors (1.0 m radius of curvature) with reflectivity of -0.997 (provided by manufacturer). The light leaked out of the cavity was collected by a compact CCD spectrometer (HR 2000). The cavity mirror reflectivity over the wavelength range of 472.3-479.3 nm was determined from the absorption of O2-O2 collisional pair. A series of concentrations of NO2 samples at high dilution were retrieved using differential spectral fitting techniques, with statistical uncertainties approaching 3.1 ppb (ng x mL(-1)) for a 80 s averaging period.