It enables capturing the morphology and dynamics of cells with optical microscopy 1 or spectroscopy techniques 2, the fabrication of parts using three-dimensional printers 3, or the treatment of skin via laser irradiation 4. The focusing of light down to a micrometric region is of prime importance in several scientific and industrial processes. The quasi-instantaneous generation of the shaped-ultrasound waves, together with the possibility to use transmission and reflection architectures, can pave the way for the real-time control of light inside living tissue. Combined with point-by-point scanning, images of samples immersed in turbid media with an optical density up to 15, similar to that of weakly scattering biological tissue, can be reconstructed.

Supported by wave optics and Monte Carlo simulations, we demonstrate how ultrasound enhances light focusing a factor of 7 compared to conventional methods based on placing optical elements outside the complex medium.

Here, we show that ultrasound waves featuring a Bessel-like profile can locally modulate the optical properties of a turbid medium to facilitate light guiding. Several approaches have been developed to address this issue, but they typically come at the cost of losing spatial or temporal resolution, or increased invasiveness. However, the scattering of light limits the depth at which current methods can operate inside heterogeneous media such as biological tissue, liquid emulsions, and composite materials. Light focusing is the primary enabler of various scientific and industrial processes including laser materials processing and microscopy.

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