Patent ID: 7798000

Claim:
A method, comprising: directing a source laser beam to a test location on a thin item, the source laser beam being amplitude modulated in a manner effective to excite a predetermined Lamb wave at a detection location of the item, the predetermined Lamb wave having zero group velocity and a finite phase velocity; sensing vibration of the item at the detection location in a frequency range in which a resonance peak corresponding to the predetermined Lamb wave is expected to be found; and detecting the resonance peak and calculating a value of a predetermined characteristic of the resonance peak, wherein the predetermined characteristic is selected from the group consisting of a center frequency of the resonance peak and a quality factor (Q) of the resonance peak, and further comprising (1) in the case that the predetermined characteristic is the center frequency of the resonance peak, converting the center frequency of the resonance peak to a corresponding thickness value representing the thickness of the item at the test location, and (2) in the case that the predetermined characteristic is the quality factor of the resonance peak, converting the quality factor of the resonance peak to a corresponding attenuation value representing the attenuation of the item at the test location.