Light Guiding with Ultrasound-Sculpted Waves

Abstract

Light control inside a sample is central in areas as relevant as life sciences and material sciences. Traditionally, this is achieved by using external devices, which can be limited by a short focal depth, scattering-limited focusing depth, and geometrical restrictions. A widely used solution consists of inserting lenses, optical fibers or mirrors directly inside a sample, as in endoscopy. However, this approach is invasive and can damage the studied medium. Recent advances in acousto-optics have shown promising results in controlling light inside media, but they usually require acoustic cavities, restricting sample geometry or compromising its non-invasiveness. Here, we show the process of designing, simulating, and developing an external ultrasound transducer that can be used to focus light inside a medium. This allowed to externally generate an ultrasound lens inside a medium, focusing pulsed light into a line. Furthermore, the focused light can be rapidly scanned in the other axis, showing potential for MHz frequency 1D scans. All while showing a high robustness against scattering, as the scanned sample could be reconstructed at up to 6 optical thickness. We anticipate that this work will be a step towards non-invasive light control inside samples.