Pulsed photoacoustic gas cell design for low pressure studies

The designing of the photoacoustic cell is critical to obtain rather good signal to noise ratio. All theoretical and experimental studies predict that for a constant light absorption, the amplitude of the photoacoustic signal reaching the microphone depends on the size of the cell and in general increases as cell dimensions are reduced. For constant laser energy and beam - cell geometry, amplitude of photoacoustic signal also depends on sample pressure. Such an effect is obvious in the low pressure region, where collisionally induced processes are dominant. Functional amplitude vs. pressure behavior is not a simple one, and must be established for any type of gas samples. Here we would like to emphasize that our attention was dedicated strictly to low gas mixture pressure region (less than 100 mbar), where some collisionally induced relaxation processes can be monitored by analyzing photoacoustic signal shape and amplitude behavior as a pressure dependent quantities.