Fig. 3: Fabrication and characterization of TUTs.

a Schematic diagram of the key steps for assembling a TUT. (MLs: Matching layers). All the procedures were executed with the stack structure fixed onto a flat glass substrate to avoid cracking and ensure the precision of machining and assembling. b Explosion view of the TUT. c Cross section of a PIN-PMN-PT-based transducer stack. d Photograph of a PIN-PMN-PT-based TUT before encapsulating with the epoxy. The signal wire of the coaxial cable is connected to the upper ITO electrode of the PIN-PMN-PT crystal. e Photograph of the PIN-PMN-PT- and LN-based TUTs. f Frequency-dependent electrical impedance of the PIN-PMN-PT-based TUT. g Ultrasonic impulse and the corresponding frequency spectrum of the PIN-PMN-PT-based TUT. h Comparison of − 6 dB fractional bandwidth relative to center frequency for current TUTs. i, j PA impulse and the corresponding frequency spectrum of the PIN-PMN-PT- and LN-based TUTs, respectively. k PA sensitivity of representative TUTs measured in similar photoacoustic microscopic imaging systems³⁵. The PA sensitivity is determined by the received voltage of the PA signal under the same condition, including the pulsed energy of the excitation laser and the gain of the ultrasonic amplifier (see Supplementary Note 4 for details on the calculation method).