2A – Fundametals of laser ultrasonics

Title2A - Fundametals of laser ultrasonics
InstructorOsamu Matsuda, Division of Applied Physics, Faculty of Engineering, Hokkaido University
Overview of topics covered

  • Optical generation of ultrasound in solids
    Thermoelastic process
    Deformation potential

  • Optical detection of ultrasound in solids
    Theory of light scattering

  • Picosecond laser ultrasonics
    Opaque medium
    Transparent medium
    Anisotropic medium
    Shear waves

  • Time-resolved imaging of surface acoustic waves
    Teomporal Fourier analysis
    Spatiotemporal Fourier analysis
    Arbitrary frequency generation/detection
    Asynchronous measurement

  • Summary

TimeMonday, October 22
AbstractIn this short course, the fundamentals of laser ultrasonics will be seen, especially focusing in so called picosecond laser ultrasonics and subjects related to it. By irradiating samples with light pulses with picosecond or sub-picosecond temporal width (pump light pulses), the acoustic waves in the frequency range up to or beyond 1 THz can be generated. Their propagation can be monitored optically by delayed light pulses (probe light pulses). The technique is called picoseconds laser ultrasonics and can be applied for various non-destructive testing/evaluation of nano-scale structures. In addition, the results involve rich information of various physical properties of the sample, such as ultrafast relaxation of excited electrons, electron-phonon interactions, thermal properties, deformation potentials, photoelastic properties, etc.. We will see the principle of the optical generation and detection of acoustic waves, and how various informations can be extracted from the experimental results.

In the later half, we will see the technique for the time-resolved imaging of GHz acoustic waves. This is an extension of above mentioned picosecond ultrasonics technique. By using a spatial scanning system of pump/probe light focusing position on the sample, the spatiotemporal evolution of the acoustic waves can be obtained. Fourier analysis reveals various aspects of the acoustic properties of the sample, such as mode patterns and dispersion relations. In the end we will see a technique to generate/detect arbitrary frequency components of the vibration even using the periodic light pulses at a fixed repetition frequency for the measurement. The technique can be further extended to allow the time-resolved imaging of the vibration generated asynchronously from the probe light source.
Short CV of Instructor Dr. Osamu Matsuda received his Dr. Sci. degree in physics from Osaka University, Toyonaka, Osaka, Japan, in 1991. In the period from 1991 to 1998, he worked as a Research Associate in Faculty of Science, Osaka University. Since 1998, he has been working as an associate professor in the Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan, specializing in particular in laser picoseconds ultrasonics, surface acoustic wave imaging, phononic crystals, and semiconductor physics.