Lithium niobate-based transparent ultrasound transducers for photoacoustic imaging

This Letter demonstrates lithium niobate (LiNbO₃)-based transparent ultrasound transducers (TUTs) for photoacoustic imaging applications. The TUTs were fabricated by coating the top and bottom surfaces of a 0.25 mm thick LiNbO₃wafer with transparent indium-tin-oxide (ITO) electrodes. The resulting transducers showed ∼80% optical transparency in the wavelength range of 690-970 nm. The TUTs had a resonant frequency of 14.5 MHz and ∼70% photoacoustic bandwidth. The versatility of the TUT approach is demonstrated by introducing two different transparent photoacoustic imaging (PAI) geometries. In one method, which suits endoscopy applications, an optical fiber of a laser diode is directly fixed on the backside of a 2.5 mm diameter TUT, and the fiber-TUT device is raster scanned to form 3D photoacoustic images. In the second method, which suits high-throughput applications, a free-space optical-only raster scanning of the laser fiber across a 1  cm×1  cm planar TUT yielded 3D photoacoustic images. The proposed TUT approach is low in cost, easy to manufacture, compatible with conventional clinical ultrasound electronics, and scalable for different configurations, including 2D TUT arrays to achieve real-time 3D high-throughput PAI.