All-optical generation and predictive modeling of focused pressure waves using Bessel beam shaping and a nanocomposite thin film.

Laser-generated ultrasound using photoacoustic materials enables high-amplitude, high-frequency ultrasound for imaging and therapy. Traditionally, focused pressure waves are achieved by shaping the photoacoustic source geometry. Here, we demonstrate that beam shaping alone can generate localized high-pressure acoustic fields. We implement an all-optical approach by illuminating a graphene-polydimethylsiloxane composite with a Bessel-like annular laser beam. This enables control of the axial position of maximum pressure up to 14 mm while maintaining nearly constant amplitude and bandwidth. The pressure field exhibits a needle-like profile with an extended axial high-pressure region up to 3 mm and lateral confinement of a few hundred micrometers. Peak-to-peak pressures up to 8 MPa were achieved at an optical fluence of 80 mJ cm⁻², with a -6 dB bandwidth of ~22 MHz. A data-driven model based on nonlinear time-reversal back-propagation reconstructs the initial pressure distribution and predicts wave propagation in homogeneous soft tissue, supporting mid-depth tissue targeting.