Combination of holographic interferometry and digital speckle system for measurement of density distributions

A digital speckle system has been combined with holographic interferometry to improve the accuracy of reconstruction of density distributions. For the combined system, several beam splitters have been used to separate the laser beams from a continuous-wave laser so that measurements can be performed simultaneously by both of the experiments. While the projections of the digital speckle system express the integration of the density gradients, those of the holographic interferometry can be obtained from the integration of the density itself. Thus, the steep region of the projections for the fringe shift of the interferometry has been measured by the use of the digital speckle system more accurately whereas the interferometry has been used to measure the projections for other regions simultaneously. CO₂ flow from a rectangular nozzle has been investigated for the proposed combined system.