Sensing of gaseous HF at low part-per-trillion levels using a tunable 2.5- mu m diode laser spectrometer operating at ambient pressure

We demonstrate a sensor based on tunable diode laser absorption spectroscopy for the detection of hydrogen fluoride (HF) gas at ambient pressure. Absorption from the HF R(1) ro-vibrational peak at nu = 4038.962 cm super(-1) (2.476 mu m) in the fundamental ( Delta nu = 1) band is measured. A quantitative spectral fit based on HITRAN data is used to account for overlapping spectral peaks of HF and water vapor, with an rms residual noise of 5 10 super(-4) absorbance units. The sensor is optimized for the detection of transient variations in HF concentration. We measure noise-equivalent concentrations for HF of 38 parts-per-trillion by volume (ppt) for 1-s integration times and 2.3 ppt for 10-min integration times.