On the establishment of a method for characterization of material microstructure through laser-based resonant ultrasound spectroscopy

Noncontacting, laser-based resonant ultrasound spectroscopy (RUS) was applied to characterize the microstructure of a polycrystalline sample of high purity copper. The frequencies and shapes of 40 of the first 50 resonant vibrational modes were determined. The sample´s elastic constants, used for theoretical prediction, were estimated using electron backscatter diffraction data to form a polycrystalline average. The difference in mode frequency between theory and experiment averages 0.7% per mode. The close agreement demonstrates that, using standard metallurgical imaging as a guide, laser-based RUS is a promising approach to characterizing material microstructure. In addition to peak location, the Q of the resonant peaks was also examined. The average Q of the laser- generated and laser-detected resonant ultrasound spectrum was 30% higher than a spectrum produced employing a piezoelectric transducer pair for excitation and detection.