Content of research

Visualization of acoustic wave propagation is extremely useful in the evaluation of physical properties and the design, fabrication and evaluation of functional devices using acoustic waves. For this purpose, we excite surface acoustic waves by irradiating the sample with an ultrashort optical pulse of subpicosecond duration (pump light), and observe their propagation with delayed optical pulse (probe light). Time-resolved two-dimensional images of the acoustic waves are obtained by scanning the delay time and the irradiation position of the probe light. The time resolution is in picoseconds, the spatial resolution is 1μm, and the frequency range is in GHz. Since this method uses a periodic optical pulse train, it was previously only possible to excite and detect acoustic waves at integer multiples of the repetition rate. However, with the newly developed technique, we have realized the excitation and detection of acoustic waves of any frequency. By developing this technique, we have also achieved image vibrations that are completely asynchronous to the repetition frequency of the optical pulse, thereby expanding the range of applications.

Potential for social implementation

• ・Measurement of acoustic resonator structures with high Q-values
• ・Dispersion relation measurement of phononic crystals
• ・Measurement of frequency response characteristics of the acoustic waveguide
• ・Design support for acoustic filter devices

Appealing points to industry and local governments

We have been studying the excitation and detection of acoustic waves in the MHz to THz frequency range, mainly using optical methods. Our research has produced good results in time-resolved imaging of acoustic waves and observation of sub-THz acoustic waves in the picosecond time range. We can provide our technology and experience to solve various problems related to acoustic wave applications.