Brillouin oscillations appear when a light pulse is diffracted in a solid by an acoustic strain pulse propagating inside the solid, and its frequency reflects elasticity of the solid. In this study, we succeeded in observing Brillouin oscillation signals for cubic boron nitride(cBN) and wurtzite boron nitride(wBN) using picosecond ultrasound spectroscopy. We developed two different optics systems using a titanium-sapphire pulse laser and a fiber laser, and adopted Al and Pt ultrathin films on the specimen surfaces as the ultrasonic sources. Although the vibration of the deposited thin film overlapped on the Brillouin oscillation, we finally succeeded in identifying the Brillouin oscillation signal and in determining the frequency.
