Re: hologram effect with water waves

> could someone explain to me how when an object gets dropped in water, and
> the resulting waves are made into a photographic plate, how can that
> photographic plate contain the size and shape of the object that was
> dropped in the water. i saw this demonstrated, and don't understand it.

I don't understand it either.

There is a process called ACOUSTIC HOLOGRAPHY where an object is placed in water, then an underwater ultrasound beam is aimed at the object, and another underwater ultrasound beam is aimed upwards at the water surface. The water surface develops very tiny standing-wave ripples, and the ripples are a hologram of the submerged object. (The two beams of sound act as the "object beam" and "reference beam" for holography.) The ripples are way too small to be directly visible to the eye.

If the ripples are illuminated by a laser, a 3D image of the original object appears, even if the water is dyed opaque black. I suppose that you could photograph the ripples, and the photograph would also be a hologram.

There was an article about acoustic holography in Scientific American magazine many years ago. They put fish in black water, and when an acoustic hologram was made, the image of the fish was a skeleton! The flesh of the fish was transparent to the sound waves, so only the bones appeared in the holographic image.