Observation of overtone vibration spectrum of water vapor using AlGaAs diode laser

Twenty-six absorption lines of water vapor in vibration-rotation band were observed using a 0.82 ??m AlGaAs diode laser in the wavelength region of 822.6-823.2 nm. The experimental principle and apparatus were described. The substraction-amplifier system used in the experimental apparatus eliminated all effect of the light variations so that the SNR (signal to noise ratio) and sensitivity of the measurement system were increased. The minimum absorption coefficient of the observed spectral line was 3??10-6 cm-1. The SNR was 60 for the spectral line which had an absorption coefficient of 1??10-4 cm-1. The effect of vapor pressure on the line-configuration and line-width was measured. The pressure broadening coefficient was 0.128 MHz/Pa close to the theoretical result of 0.11 MHz/Pa.EI03256-2601