A desensitized displacement interferometer applied to impact recovery experiments

A variable sensitivity displacement interferometer (VSDI) used to monitor both normal and in-plane particle displacements in stress wave propagation experiments is introduced. The general system consists of two interferometers working in tandem. Normally reflected light is interfered with each of two symmetrically diffracted light beams generated by the specimen rear surface. In cases where the surface motion simultaneously exhibits both in-plane and normal displacements, the fringes represent a linear combination of the longitudinal and transverse components of motion. Decoupling of the normal and in-plane displacement histories can be achieved through a linear combination of the two VSDI records. The variable sensitivity feature of the VSDI greatly desensitizes normal displacement measurements and is particularly well suited for wave propagation studies. Experimental results are presented which demonstrate the application of this technique to monitoring particle motion histories in pressure-shear recovery experiments.