# Non-Contact and Real-Time Measurement of Kolsky Bar with Temporal Speckle Interferometry
## 3 Experiment and Results
### Verification Experiment of In-Plane Displacement Measurement Capability
After the speckle verification is completed, we replaced the iron plate with the incident and transmitter bars continue to verify the in-plane displacement measurement capability of the measurement system. To accurately test the in-plane displacement measurement capability of the measuring system, the verification experiment was performed without a sample and the striker bar was driven with a very low velocity of a few microns per second. The translation stages push the striker bar at a slow velocity so that it strikes the incident bar at a certain velocity. The intensities of the speckles on the incident bar and transmitter bar are changed in the time domain. These changes are collected by the CCD camera. The frame rate of the CCD camera is 120 frames/s. The whole measuring time is five seconds and an arbitrary point on the position of incident bar and transmitter bar is chosen as the test point, the  
Figure 6: Verification experiment setup: 1 and 18 are green lasers; 2 and 16 are beam filters; 3 and 17 are spatial filters; 4 and 13 are beam splitters; 5 is a grating ruler; 6, 9, 11, and 15 are reflectors; 7 and 14 are CCD; 8 is the trigger device; 10 is the translation stage; 12 is an oscilloscope; 19 is the SHPB device. In the verification experiment, the incident angle of the incident and transmitter bars is 70 degrees and 72.5 degrees, respectively. The actual displacement of the grating ruler is 7.7 \(\upmu\)m, and the actual average velocity of the bar is 1.54 \(\upmu\)m/s. The displacement of the incident bar obtained by the CCD camera is shown in Figure 10. As can be seen from the figure, the displacement processed by our algorithm is 7.68 \(\upmu\)m and the average velocity is 1.536 \(\upmu\)m/s. Therefore, the measured error of displacement is 0.02 \(\upmu\)m and the measured error of velocity is 0.004 \(\upmu\)m/s. The relative error of displacement and velocity are both 0.26%. The displacement of the transmitter bar obtained by the CCD camera is shown in Figure 11. As can be seen from the figure, the displacement processed by our algorithm is 7.68 \(\upmu\)m and the average velocity is 1.535 \(\upmu\)m/s. Therefore, the measured error of displacement is 0.02 \(\upmu\)m and the measured error of velocity is 0.005 \(\upmu\)m/s. The relative error of displacement and velocity are 0.26% and 0.32%, respectively. In order to verify the repeatability of the measurement system, we have also designed the system for multi-detection points processing. The measured results of two bars are shown in Table 2, where A1 to A5 are the points on the incident bar, and B1 to B5 are the points on the transmitter bar, as shown in Figure 9. From Table 2 we can see the displacement error of the incident bar and transmitter bar are less than 0.04 \(\upmu\)m and 0.05 \(\upmu\)m and the velocity error is less than 0.008 \(\upmu\)m/s and 0.006 \(\upmu\)m/s, respectively. Figure 10: The in-plane displacement of the incident bar: (**a**) the intensity distribution over time; (**b**) the discontinuous phase map obtained by wavelet transformation; (**c**) the measured displacement over time; (**d**) average speed. As can be seen above, the results of these verifications experiment prove that the measurement system has a very good in-plane displacement measurement capability, and the algorithm we developed can accurately calculate the information of displacement and velocity.