On the accurate determination of pressure-induced line shifts in the 2 nu(3) band of H2O at 1320 nm

A simple technique is demonstrated for the accurate determination of pressure-induced line shifts of water in air. High- and low-pressure water samples are simultaneously probed on selected overtone transitions at 1.32 μm using a current-modulated distributed-feedback diode laser and harmonic detection. The resultant profiles yield an average line shift of -293 ± 30 MHz/atm for the 3, 3, 0 (002) ← 2, 2, 1 (000) transition at 227251 GHz and -134 ± 7 MHz/atm for the 3, 2, 1 (002) ← 2, 1, 2 (000) transition at 227027 GHz. Comparisons are made between first- and second-harmonic detection, and wavelength- and frequency-modulation regimes. The effect of modulation broadening on the returned line shifts is quantified