Tailored Photoacoustic Apertures with Superimposed Optical Holograms

A new method of generating potentially arbitrary photoacoustic wavefronts with optical holograms is presented. This method uses nanosecond laser pulses at 1064 nm that are split into four time-delayed components by means of a configurable multipass optical delay apparatus which serves to map the pulses onto phase-delayed regions of a given acoustic wavefront. A single spatial light modulator generates separate holograms for each component which are imaged onto a photoacoustic transducer comprised of a thermoelastic polymer. The spatially- and temporally-modulated holograms facilitate a phased array effect which enables beam steering of the resulting acoustic pulse. For a first experimental demonstration of the method, as verified by simulation, an acoustic beam is steered in four directions by around 5 degrees.