Verification of acoustic mismatching model for sub-THz acoustics in glass

Because of high acoustic attenuation of glass in sub-THz regime, it is difficult to measure the highly damped acoustic waves passing through the media. In theory, the acoustic properties of the media could be experimentally studied by reflection of acoustic waves which do not propagate into the media. Complex acoustic impedance, which includes the information of dispersion relation and frequency-dependence of attenuation, is a parameter in the acoustic mismatching model to describe the phenomena when acoustic waves encounter the interface of media. The mismatch of acoustic impedance results in reflection and transmission of acoustic waves at the interfaces. We report the verification experiments for this model in sub-THz regime. We generated coherent THz acoustic phonons and measured the amplitude and phase of the reflected acoustic phonons from the interface of GaN and silica. Based on the acoustic mismatching model, the frequency dependence of sound speed and the attenuation were obtained up to 0.3 THz. These values were compared with the results from typical method. This verified technique enables the measurement of sub-THz acoustic properties of thick and highly damped materials.