projectile and target assembly is shown in Fig. \[fig:targetassembly\](a), while a labeled picture of the target assembly mounted onto the gas gun can be seen in Fig. \[fig:targetassembly\](b).

![image](targetassembly-eps-converted-to.pdf){width="1.6\columnwidth"}

Plate-impact experiments rely on measuring the time evolution of the free-surface velocity to determine the spall strength of the material being studied. [@Antoun2003] The use of aluminized Mylar, which is reflective to infrared radiation, allowed the free-surface velocity to be monitored by a photonic Doppler velocimetry (PDV) system. [@Strand2006] PDV measures surface velocity by observing the variation in beat frequency between a laser beam reflected off a moving surface and a reference beam. The system has a trade-off between time resolution and velocity accuracy, due to the fact that the beat frequency is obtained by performing a sliding window fast Fourier transform (FFT). [@Dolan2010] A window sample size of 2000 to 3000 samples was used during the sliding FFT analysis, resulting in an estimated velocity uncertainty of 2 m/s and a time resolution of approximately 10 ns. Figure \[fig:samplespectrogram\], shows a typical spectrogram produced by performing a sliding window FFT on the PDV data, where the high intensity contours represent the velocity of the free surface. The extracted velocity–time curve for 