A technique has been developed to measure the change in birefringence along the axis of shock propagation, probing the relative refractive indices of the material perpendicular to shock propagation. Experiments were performed on calcite single crystals and the results compared to previous literature studies on calcite quasi-static behaviour. Interface velocities are determined using fibre based homodyne Photon Doppler Velocimetry (PDV) operating at 1550 nm whilst the birefringence technique uses free space 532 nm optics. A change in birefringence of Δn = 0.0029 ± 0.0001 was observed. This was higher than the predicted change found using a hydrostatic model based on previous studies.