[Spatial and temporal control of ultrasonic fields via optoacoustic holography]

The present paper presents a new method for generating ultrasound, based on the interaction of laser-induced ultrasound generation and ultrasonic holography. An ultrasonic field generated in a water tank via the optoacoustic effect is spatially and temporally controlled: In order to produce defined ultrasonic frequencies in the MHz range, the laser pulses incident on a light-absorbing layer are modulated in time using an electro-optic modulator (EOM). Additionally, a high-resolution liquid crystal spatial light modulator (SLM) is used to imprint a pre-calculated phase front to the laser beam. A computer-generated binary hologram is also displayed at the SLM. The expanded laser beam projects the corresponding pattern to the plane absorptive layer in the water tank. The projection of specific patterns for the generation of ultrasonic beams resembles the use of, diffractive optical elements" in optics. Optical ultrasound generation with holographic steering is a flexible tool with promising numerous new applications in medical and technical ultrasound diagnostics.