Although transparent materials with birefringent properties (e.g., solar panels and separator films for secondary cells) are common, damage detection during the manufacturing process is crucial to economically realize high-quality materials. Herein a method using a pulsed-laser and a high-speed polarization-imaging camera is proposed to rapidly detect damage, including scratches and dents, in transparent materials. Specifically, as stress waves, which are generated by a non-contact impulse excitation from laser ablation, propagate through a material, the stress concentrations induced around damage are measured as the two-dimensional birefringent phase differences using a high-speed polarization-imaging camera with a microsecond-order temporal resolution. When stress is dominant, the distribution of the measured birefringent phase difference can be considered the relative distribution of stress. Using acrylic plates as a representative transparent material with several hundred micrometers of damage (e.g., a dent or a scratch), we demonstrate that the proposed method detects damage in a very short timeframe of several microseconds.
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