While photonic Doppler velocimetry (PDV) is becoming a common diagnostic for tracking
velocity in shock physical experiments, its validity on measuring surfaces with different
reflectivity is not studied. This paper investigates the effects of surface reflectivity on PDV
measurement for tracking back free surface velocity in laser shock processing. Credible
measurement results for coarse polished surfaces with low reflectivity are obtained, whereas
fine polished surfaces with relatively high reflectivity lead to heterodyne fringes with high
frequency and corresponding unreasonably fast velocities. This phenomenon reported in the
paper is somewhat inconsistent with the general view that PDV has remarkable robustness to
large changes in surface reflectivity. The reason might be ascribed to multiple reflections of
light, which cause the generation of multiple Doppler shifts. The mixing of the reference light
and those Doppler-shifted lights brings out high frequency heterodyne fringes resulting in high
velocity. Low surface reflectivity is better suited for PDV measurements.
This work is funded by the Instrument Project of Chinese Academy of Sciences (CAS) (grant no. YZ200930); additional funding is also provided by the National Natural Science Foundation of China (NNSFC) (grant no 11332011).