TWO WAVELENGTH DIGITAL HOLOGRAPHIC INTERFEROMETRY FOR INVESTIGATION OF DYNAMIC PROCESSES IN FLUID MECHANICS
Interferometric methods such as digital holographic interferometry and interferometry are generally understood to belong to the group of most accurate measuring devices. However, due to the bounded nature of a light wave, the measurement range given by the unambiguity is squeezed within the range of one cycle of the wave. The measurements are therefore relative and limited to small gradients. This paper reports on a new approach to measure dynamic processes in fluid mechanics using two-wavelength digital holography with extended dynamic range. A key factor is to capture a digital hologram including information of the both wavelengths. Such digital hologram is further reconstructed and processed in order to retrieve optical phase map with extended range. As a result, absolute measurement with interferometric accuracy can be achieved. The method principle and preliminary experimental results are introduced in the paper.