Precision Measurement of the Group Velocity of Ultrasound in Samples with Millimeter Thickness

A methodology is proposed for high-precision local measurement of the group velocity of longitudinal waves in solid samples with millimeter thickness. Achievement of the required accuracy involves laser thermo-optical excitation of submicrosecond ultrasonic video pulses and ultrawideband piezoelectric recording of acoustic signals reflected from the test sample. Plane-parallel samples made of duralumin, quartz, and steel with a thickness of 2–6 mm are studied. To achieve the required accuracy in measuring the group velocity of ultrasound, the signal shape is mathematically processed with compensation for diffraction of the ultrasonic beam as it propagates through the sample. The possibility of ensuring the uncertainty in measuring the group velocity of ultrasound in the 1–15 MHz frequency range at a level of 0.1% in samples with millimeter thickness is demonstrated.