Investigation of the absorption saturation due to a vibrational–rotational transition in $H_2O$ using an optoacoustic method

An optoacoustic spectrometer was used to make an experimental investigation the absorption saturation due to a vibrational-rotational transition in $H_2O$ vapor under the action of ruby laser radiation in the transient interaction region. Some features of the performance of the optoacoustic method are analyzed at high exciting radiation intensities and analytic expressions are derived to describe the saturation behavior of the signal recorded by the optoacoustic spectrometer. It is found that the rate of saturation of the recorded signal is lower than the rate of saturation of the true absorption coefficient.