Laser based Non-Contact method for Nonlinear Mixing of Rayleigh waves

This study presents the nonlinear mixing technique of two co-directionally tr velling Rayleigh surface waves generated and detected using laser ultrasonics. The optical generation of Rayleig h waves on the specimen is obtained by shadow mask method. In conventional nonlinear measur ements, the inherently small higher harmonics are greatly influenced by the nonlinearites caused by coupling variabilities and surface roughness between the transducer and specimen interface. The proposed technique is completely contactless and it should be possible to eliminate this problem. Moreover, the nonlinear mixing phe nom non yields not only the second harmonics, but also the sum and difference frequency components, which can be used to measure the acoustic nonlinearity of the specimen. In this paper, we will be addressing the experimental configurations for this technique and the finite element analysis to characterize the acoustic nonlinearity of t he Aluminum 7075 alloy specimen.