Localized dynamic lensing with instantaneous extended depth of field via collinear light–sound interactions

Abstract Tunable acousto-optic (AO) lenses have recently emerged as versatile tools for optical beam shaping, imaging, and particle manipulation. Conventional AO lenses rely on light propagating orthogonally to a standing ultrasonic field, producing Bessel-like beam patterns via the Raman–Nath effect that compromise focal localization and depth of field (DoF). Here, we introduce a novel class of AO lenses based on a three-dimensional, dynamically variable refractive index profile generated by a z-axis-scanning focused ultrasound transducer. By exploiting co- and counter-propagating light–sound interactions over an extended axial range, we achieve fully controllable, localized optical focusing with an instantaneous extended DoF. We demonstrate dynamic tuning of focal position, lateral resolution, and optical power throughput by adjusting ultrasound parameters. This approach offers a promising platform for applications requiring precise remote focusing, three-dimensional micromanipulation, and deep tissue imaging or therapy. Graphical Abstract