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Optical detection of ultrasonic leaky waves from solids in air

A recently developed optical heterodyne interferometer is proved to be sensitive to detect ultrasonic waves leaking out from solids at centimeters away from the metal surface in air. This measurement is based on the detection of the optical index variation in air due to the leaky wave. This optical method can be used for metals with low reflectivity surfaces. Thus it can be used for non-polished surfaces and can be extended for non-contact nondestructive evaluation applications.