In situ 3D reconfigurable ultrasonically sculpted optical beam paths.

We demonstrate that optical beams can be spatially and temporally shaped in situ by forming 3D reconfigurable interference patterns of ultrasound waves in the medium. In this technique, ultrasonic pressure waves induce a modulated refractive index pattern that shapes the optical beam as it propagates through the medium. Using custom-designed cylindrical ultrasonic arrays, we demonstrate that complex patterns of light can be sculpted in the medium, including dipole and quadrupole shapes. Additionally, through a combination of theory and experiment, we demonstrate that these optical patterns can be scanned in radial and azimuthal directions. Moreover, we show that light can be selectively confined to different extrema of the spatial ultrasound pressure profile by temporally synchronizing lightwave and ultrasound. Finally, we demonstrate that this technique can also be used to define spatial patterns of light in turbid media. The notion of in situ 3D sculpting of optical beam paths using ultrasound interference patterns can find intriguing applications in biological imaging and manipulation, holography, and microscopy.

Ultrasonic sculpting of virtual optical waveguides in tissue.

Optical imaging and stimulation are widely used to study biological events. However, scattering processes limit the depth to which externally focused light can penetrate tissue. Optical fibers and waveguides are commonly inserted into tissue when delivering light deeper than a few millimeters. This approach, however, introduces complications arising from tissue damage. In addition, it makes it difficult to steer light. Here, we demonstrate that ultrasound can be used to define and steer the trajectory of light within scattering media by exploiting local pressure differences created by acoustic waves that result in refractive index contrasts. We show that virtual light pipes can be created deep into the tissue (>18 scattering mean free paths). We demonstrate the application of this technology in confining light through mouse brain tissue. This technology is likely extendable to form arbitrary light patterns within tissue, extending both the reach and the flexibility of light-based methods.