Vibration testing based on impulse response excited by laser ablation

This paper proposes a vibration testing system based on an impulse response excited by a laser ablation. In conventional vibration testing using an impulse hammer, high frequency elements of over tens of kilohertz are barely present in the excitation force. A high-power YAG pulse laser is used in this system for producing an ideal impulse force on a structural surface. By illuminating a point on a metal with a well-focused (2 μn) YAG laser, atoms, electrons and ions etc. are emitted from the metal. As a result, an ideal impulse excitation force generated by laser ablation is applied to a point on the structure. Therefore, it is possible to measure high frequency FRFs (Frequency Response Functions) in this system. Additionally, a water droplet overlay on the metal is used to adjust the force magnitude of laser excitation. An aluminum block that has nine natural frequencies below 40 kHz is employed as a test piece. The system is validated by comparing the FRFs of the block obtained using laser excitation, an impulse hammer, and FEM. In addition, the relationship between accuracy of FRF measurements and sensitivity of sensors is investigated.