Probing the spatial impulse response of ultrahigh-frequency ultrasonic transducers with photoacoustic waves

Characterizing the radiated or received acoustic field of ultrasonic transducers using the spatial impulse response (SIR) represents an important step in testing, design, and optimization of ultrasonic transducers. However, for the ultrahigh-frequency acoustic field, conventional methods, such as the hydrophone method and the small-ball reflection method, are limited by narrow bandwidth and poor spatial resolution. Here, we propose a method to obtain the transducer's SIR through its response to photoacoustic waves, which allows high-precision acoustic field measurements, with spatial resolution as fine as 1.7 μm. We subsequently measure the SIRs of two focused ultrasonic transducers, with 20 and 93 MHz center frequencies, and confirm that the three-dimensional acoustic fields can be accurately reconstructed using the angular spectrum approach. More importantly, this method is unique to receive-only ultrasonic detectors, the SIR of which could not be measured previously with conventional methods, and it could facilitate ultrasonic transducer design, as well as other related fields, such as nondestructive evaluation, biomedical imaging, and particle manipulation.