Multi-depth focused laser differential interferometer based on chromatic aberration

A modified version of focused laser differential interferometry (FLDI) is demonstrated with adjacent beam pairs distributed along the optical axis. This feature is accomplished using two different wavelengths of light in the interferometer and accounting for the chromatic aberration of the lenses in the optical setup. It is demonstrated that ray trace calculations can be modified to predict the focal points of each of the two different colored beams, and experiments using a tube jet and a laser-induced blast wave show the instrument still has the expected features of an FLDI as well as continued capability for velocimetry. This modification is in effort to allow FLDI to be used for the analysis of three-dimensional flows, especially if combined with other multi-point variations and targeting high-frequency flow content.