This is very much like the process used in holographic photography, at least the schematic is almost identical. In both a beam of light is converted to laser light by passing through a crystal. The internal structure of the crystal organizes the light into patterns that give laser light special properties. One way to think of it is that the crystal is full of tiny mirrored facets that line up the photons and shoot them out in lockstep.
The laser beam is then split in two by passing through glass that reflects a percentage of the light toward a mirror. The mirror reflects the beam at the medium. The unreflected light continues through the object, and on to the medium. There it intersects the other beam and forms an interference pattern. The object has altered the main beam, while the mirrored beam is still pure.
I think you could say that the interference patterns represent the difference between the structure of the two beams.
In holographic photography, the interference pattern is recorded on light sensitive film. Where this system is different is that it records the interference patterns “inside” the crystal or photopolymer medium. The laser interference patterns are recorded by altering the internal structure of the medium. This eliminates the possibility of errors from surface scratches or dust.
For binary data storage we can use an object that is a fine grid, with units the width of a wavelength of this laser light. Each cell of the grid represents a binary bit, either letting light thru or blocking it. A square centimeter of this grid will hold a lot of binary data.
Another separate hologram can be recorded in the same media, by slightly changing the angle between the media and beam. Still more information can be stored by changing wave length or phase of the laser. If we rotate the medium and make our laser light variable, we can cram a lot of data into a very small space.
Besides being able to store a lot of data, retrieval is in huge chunks of binary bits at a time rather than a linear stream. This technology has the potential to be the next big deal in computer data storage.
What is really the key here is that holographic memory records interference patterns by “altering the internal structure of the medium”. The fact that interference patterns can do this needs to be looked into further.