Simulation, modeling & verification of velocity interferometer in high strain rate experiments

Linear Time Invariant (LTI) model of optical velocity interferometer system used for measurement of time resolved velocity profile of moving object/surface has been developed. The working of this instrument is based on the measurement of the differential Doppler shift as a function of time, by beating two light signals reflected from moving surface of the target material, at two different instants of time separated by a small time interval of the order of a fraction of nanosecond to a few nanoseconds. The developed model is simulated and characterized in time as well as in frequency domain. The validation of the model has been carried out using correlation between the phase profile (equivalently fringe shift) measured in high strain rate (~104 s-1) experiments and that predicted by the model using velocity profile as input generated from the hydrodynamic simulations. The cross-correlation coefficient and magnitude squared spectral coherence coefficient values close to 1 indicate that the simulation is fairly close to the experiment.