1. Acoustic imaging apparatus which comprises means for generating an acoustic wave beam along a predetermined path, means supporting an object to be imaged in said acoustic beam path, a plurality of visible particles suspended throughout a fluid medium for displacement in the beam path beyond the object in proportion to the intensity of radiation pressure resultant from the acoustic energy, said particles being suspended in a thin layer of liquid disposed between enclosing layers of material whose optical indices of refraction are less than that of the suspending liquid, to define an optical waveguide and means for directing light through said liquid layer between said enclosing material layers, whereby essentially only light reflected from said particles will form an optical image of said object.