Three-dimensional gas concentration and gradient measurements in a photoacoustically perturbed jet

The 3-D measurement of the gas concentration in a photoacoustically forced gas jet is described. A pulsed laser focused onto a laminar gas flow was used to trigger a localized disturbance which evolved with time. After a fixed time delay, the gas concentration in a 2-D cross section of the jet was measured by recording Rayleigh scattering from a second laser used to illuminate a thin sheet intersecting the flow. A series of these 2-D measurements made at the same time delay resulted in a full 3-D mapping of structures within the flow. Computer graphics enabled the subsequent reconstruction and visualization of the 3-D surfaces of constant concentration as well as the magnitude of the concentration gradient on such surfaces.