A Focused Optically Transparent PVDF Transducer for Photoacoustic Microscopy

Abstract

This papers reports the development of a novel focused optically-transparent ultrasound transducer with a wide bandwidth for photoacoustic microscopy (PAM). It consists of a 9- $\mu \text{m}$ -thick polyvinylidene fluoride (PVDF) film coated with Indium-tin oxide (ITO) and metal electrodes, which is laminated onto a concave glass lens. A new fabrication process was developed to ensure the formation of continuous ITO coatings on the curved transducer surface without fracturing. Both optical and acoustic experiments were conducted to characterize the performance of the transducer. The testing results show that the transducer has an optical transmittance of 60% (@ 532 nm), an acoustic center frequency of 24 MHz, and an acoustic bandwidth of 26 MHz. With an acoustic numerical aperture (NA) of 0.23, it provides a 0.13-mm acoustic focal spot and a 1.6-mm focal depth. For demonstration, a PAM setup was built for conducting PA imaging on different targets. In contrast to existing PAM systems, the use of the optically-transparent focused transducer allows a simpler and more compact configuration and easier alignment of the optical excitation and acoustic focal points. Such features are especially useful for the development of miniaturized PAM systems for handheld, wearable and even endoscopic applications.