Versatile and scalable fabrication method for laser-generated focused ultrasound transducers

A versatile and scalable fabrication method for laser-generated focused ultrasound transducers is proposed. The method is based on stamping a coated negative mold onto polydimethylsiloxane, and it can be adapted to include different optical absorbers that are directly transferred or synthesized in situ. Transducers with a range of sizes down to 3 mm in diameter are presented, incorporating two carbonaceous (multiwalled carbon nanoparticles and candle soot nanoparticles) and one plasmonic (gold nanoparticles) optically absorbing component. The fabricated transducers operate at central frequencies in the vicinity of 10 MHz with bandwidths in the range of 15–20 MHz. A transducer with a diameter of 5 mm was found to generate a positive peak pressure greater than 35 MPa in the focal zone with a tight focal spot of 150 μm in lateral width. Ultrasound cavitation on the tip of an optical fiber was demonstrated in water for a transducer with a diameter as small as 3 mm.