OAD signal generation in absorbing gas-hydrogen mixtures
A.N. Kuryak, D.A. Pomazkin, B.A. Tikhomirov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: optoacoustic detector, sensitivity, pressure, gas type dependence, hydrogen
Abstract
The reasons are found for a decrease in the sensitivity of a TROA (time-resolved optoacoustic) detector in spectrometers with pulsed lasers and of a non-resonant OA detector in spectrometers with cw lasers when buffer gas nitrogen (air) is replaced by hydrogen in mixtures with an absorbing gas. In the first case, the reason is the high speed of sound in hydrogen at an insufficiently wide working frequency band of the microphone. In the second case, the reason for the loss of sensitivity is the low dynamic viscosity of hydrogen, which results in faster pressure equalization in the pre- and behind-membrane volumes of the OA detector chamber for a light pause as compared to heavier molecular gases. Therefore, the amplitude of an OA signal at the modulation frequency of the cw laser radiation increases in proportion to the dynamic viscosity of the gas.
|
