Laser-generated focused ultrasound for arbitrary waveforms

Transducers for laser generated focused ultrasound can achieve photoacoustic waves with several hundred bars positive pressure in water. Previous designs employed concave glass substrates decorated with catalytically grown carbon nanotubes. Here, we show that arbitrarily shaped surfaces made of polymers and printed with 3d printers allow the generation of waveforms with complex temporal and spatial shape. We first present three different polymer materials together with a simplified deposition technique. This is achieved by painting layers of carbon-nanotube powder and polydimethylsiloxane. Together with a clear resin (Formlabs Photopolymer Clear Resin), pressure amplitudes of 300 bar peak positive were obtained. With the flexibility of polymer substrates, complex waveforms can be generated. This is demonstrated with a stepped surface which launches two waves separated by 0.8 μs. Detailed pressure measurements are supported with shadowgraphy images and simulations of the wave.