Fiber optic laser probe for acoustic wave measurements

An optical probe has been developed for acoustic surface waves using single-mode fiber to illuminate the sample. The scanned fiber probe has an effective spot size of 4 μm without the use of focusing lenses. 34% of the incident light re-enters the fiber from a specular reflector. The signal from the sample is combined with a reference in a single fiber, eliminating misalignment in the interferometric measurement. Experimental results are presented for a LiNbO3 focused transducer surface acoustic wave (SAW) device. On this device, the probe exhibits 60-dB dynamic range and 3×10−2 Å minimum sensitivity. The resolution, sensitivity, and flexibility of the fiber probe make it applicable to crack detection in nondestructive testing.