## 3 Results
### Detected Waveform Evolution
Based on the high pulse energy results for the baseplate only, the V-shape evolves with propagation distance through the formation of an initial wing at 16, 20 and 24 mm. That is, the waveform starts upward before the downward slope of the V-shape. For these waveforms the peak-to-peak amplitude is defined by the first segment of the V-shape since the segments have different lengths. The results for high pulse energy on the AM deposition in Figure 6 indicate that normalizing the AC signal with respect to the DC level did not eliminate the scatter between trials, suggesting that the scatter is not associated with surface reflectivity. To assess whether the scatter is due to source variability (whether from the surface or the pulsed laser itself) we observe that the peak-to-peak amplitude for trial 1 is significantly lower than trials 2 and 3 for propagation distances of 4-16 mm, but then increases to be the largest at 24 mm. Hence, the scatter does not appear to be due to source variability. For high pulse energy the peak-to-peak amplitude for the AM deposition generally increases between 4 and 12 mm and then decreases between 12 to 24 mm (Figure 7b), which is a strong indicator of cumulative nonlinearity that becomes overwhelmed by attenuation (starting at 12 mm). To the contrary, the peak-to-peak amplitude for low pulse energy remains essentially constant. In addition, the V-shaped waveform has strong asymmetry due to the presence of an initial wing and because the first leg of the V-shape is much steeper than the second leg for high pulse energy. Moreover, the second leg of the V is often curved. Figure 7a shows idealized sketches of the low pulse energy and high pulse energy V-shaped waveforms. We analyzed the steepening of the first leg of the V-shape with propagation distance for the AM deposition by computing the absolute value of the slope in the middle portion of the peak-to-peak distance. The results in Figure 8 have significant scatter, but the average steepness increases by a factor of almost two for propagation distances of 4-16 mm before it decreases. It appears that the scatter in Figure 8 appear may be due to the low amplitudes for Trial 1 observed in Figure 6.  
The \(u_{3}\) waveforms in Figure 6 were differentiated with respect to time to derive the \(v_{3}\) waveforms plotted in Figure 9. Since the \(u_{3}\) waveforms were not calibrated to actual displacements in nm the \(  
followed by a positive peak. However, in many cases in Figure 9 the following positive peak is larger than the initial negative peak in the \(v_{1}\) waveform. Figure 6: Sample \(u_{3}\) displacement waveforms for Ti-6 Al-4V received by laser interferometer after propagation distances of 4–24 mm for baseplate and AM deposition. Figure 7: (**a**) Schematic representatives of V-shaped waveforms in Figure 6 for low pulse energy and high pulse energy. (**b**) Normalized peak-to-peak amplitude evolution with propagation distance for Ti-6 Al-4V AM, with mean and standard deviation. Figure 8: Steepness of Ti-6 Al-4V AM waveforms in Figure 6 as a function of propagation distance, with mean and standard deviation. Figure 9: Sample \(v_{1}\) and \(v_{3}\) velocity waveforms derived from the displacement waveforms in Figure 6.