Adaptive geometric optics derived from nonlinear acoustic effects

Tunable gradient index (GRIN) lenses were formed in a liquid-filled cavity supporting an ultrasonic standing wave. The refractive index gradient is based on the steady-state pressure component of the finite-amplitude acoustic signal. An acoustic lens was constructed which (1) focused and modulated a collimated light source and (2) formed an image. The properties of the lens are a function of the amplitude and frequency of the applied ultrasound. At the center of symmetry, the device can be approximated as a diverging lens with a single focal point of about −10 cm. In general, however, a series of focal lines are formed, to create a device resembling an axicon or an abberrating lens.