On laser-induced ultrasound generated in a thin semi-transparent layered polymer structure

Abstract

We investigate laser-induced ultrasound generated in a plane semi-transparent layered polymer structure. The scope is to study relations between generated ultrasound, as e.g. amplitude, and centre frequency and bandwidth of its frequency spectrum, and properties of the polymer layers, like thickness and absorption. This knowledge can then be used when designing polymer film based, semi-transparent ultrasonic devices specifically for photoacoustic applications. The experimental study is set-up as a factorial experiment with a completely randomised design.In the experiments, the light source is a pulsed Nd:YAG laser. As absorber, a semi-transparent, non-conductive polymer film in a plane layered structure of one or more layers on a glass substrate is used. The frequency spectra of the generated ultrasound spans 2 to 20 MHz, which is recorded by a broadband PVDF ultrasonic transducer. The results show that an increased thickness of the polymer layer structure relate to a lower center frequency and a lower bandwidth, and that an increased optical absorption and a decreased layer structure thickness is related to a higher ultrasound amplitude.

Combined physical and statistical modeling of laser induced ultrasound signals from thin light absorbing films

“…Experiments were performed on laser-induced ultrasound in samples of a layer of stacked dyed PET polymer film mounted on glass substrate and immersed in water [15], see Fig. 1.…”