Effect of coupling gas viscosity on the photoacoustic signal

Abstract
The phase angle φ of a gas-coupled photoacoustic (PA) signal has been measured as a function of coupling gas column thickness lg for a ‘‘one-dimensional’’ PA cell. The PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface of silicon. We show that the observed data can be explained in a PA model including the consideration of a residual volume in the PA cell, together with the consideration of viscous damping of the PA signal at small lg.