Fig. 1: In situ imaging using ultrasonically sculpted virtual relay lens.

a Schematic of a traditional GRIN lens used as an endoscope inserted in the target medium to relay the image of a target object to an external microscope; b ultrasonic waves sculpt a virtual GRIN lens in the medium, effectively creating a relay lens. c Axial; and d cross-sectional profiles of the ultrasonically modulated refractive index profile in the medium. e The input light wave experiences a radially-varying phase delay because of the refractive index profile, which is maximum at the center; as a result, the beam of light will adiabatically converge to a central focal spot. f Schematic of the experimental setup used for demonstrating the relay imaging capability of the virtual GRIN lens; inset: illustration of the target object (not to scale), which is placed 29 mm deep into the medium from the focal plane of the external microscope. g Out-of-focus image of the target object when ultrasound is off. h When ultrasound is turned on, the image of the target object relayed through the medium and resolved by the external microscope. The exposure time used for acquiring Fig. 1g is 5-folds higher than the value used for Fig. 1h