Diode laser based photoacoustic humidity sensors

Various diode laser based photoacoustic (PA) systems applied in water vapour detection are presented. The dependence of the systems’ performance on the physical and chemical properties of the measured gas is discussed. It was found that the pressure dependence of the measured PA signal is different for amplitude and wavelength modulated lasers. This difference is explained. Linearity in a concentration range of more than four orders of magnitude in combination with typical accuracy of a few percentages was proved.