Precise regulation of photoacoustic frequency for all-optical ultrasound endoscopic imaging

All-optical ultrasound imaging has exhibited notable potential for application in endoscopic imaging. However, the frequency control of the laser-induced ultrasound is still a challenge. Here, we demonstrate theoretically and experimentally an effective way to improve the operational frequency of photoacoustic devices by regulating the characteristics of the light-absorption layer and thermal expansion layer. Additionally, utilizing the as-fabricated CSNP - PDMS / SiO 2 composite material, a fiber-integrated side-looking photoacoustic device is successfully developed with a central frequency of 20 MHz and a bandwidth of 156% at −6 dB . Most importantly, a high-resolution all-optical ultrasound endoscopic (AO-UE) imaging system is assembled, achieving an axial resolution of 54 μm, much better than that of piezoelectric ultrasound endoscopy with the same operational frequency. Then, the high-resolution intracavitary ultrasound images of rabbit tracheas, blood vessels, and intestines are obtained ex vivo . All these encouraging findings provide new insights into the frequency control of photoacoustic devices and endoscopic ultrasound technology, facilitating future medical imaging applications.