Nano-second Laser-induced Plasma Shock Wave in Air for Non-contact Vibration Tests

Herein a vibration test method is discussed based on a non-contact, non-destructive excitation input using a laser-induced plasma (LIP) shock wave and a non-contact input estimation using Newton’s second law of motion. We have previously introduced a non-contact vibration test method using an excitation force generated by laser ablation, but it cannot be used when the target structure is lightweight, fragile, and small-sized because a crater with a diameter of several micrometers is created. The LIP generates a highly reproducible shock wave, which become an excitation force to a target structure. This shock wave depends on the gas density, gas specific heat ratio, laser fluence, and ambient environment. If these parameters are constant, the LIP excitation force can be estimated beforehand, allowing only the output measurement to determine the frequency response measurement of an input–output relationship of the target structure. After calibrating the LIP excitation, the frequency response function of a target structure can be obtained.