Figure 8: Laser-induced projectile impact test.

(a) Diagram of the optical setup for LIPIT. (b) The speed of the μ-projectiles is proportional to the square root of the excitation pulse energy for a given thickness of the absorbing polymer layer. The error bar represents the maximum and minimum speeds for each median value and the green line is a fitting curve. (c) Double exposure photograph with a 22-ns interval at 250 ns after the excitation laser pulse. The scale bar is 200 μm. (d) Expanded section of (c). Here, each μ-projectile appears twice; for example, the μ-projectile marked as ‘A’ is the same μ-projectile marked as ‘B’ and the corresponding speed is 3.4 km s⁻¹. Only the μ-projectiles outside of the shock front present a Mach cone, appearing when an object’s speed exceeds the speed of sound. The sizes of the μ-projectiles appear differently depending on their distance to the microscope objective lens. The scale bar is 100 μm.