How are holograms possible?

On this very topic, this might be one of my most favorite videos ever single-handedly changing my understanding of holograms: ▶ this video

Yea I have some ideas, but I haven't found an easy way to implement it yet. The term of art that I'm exploring is called "Holographic Interferometry". Sibling poster gave you a link to regular interferometry. But basically, if you split the laser beam, one goes straight into the camera sensor, and the other off your object, you can do some pretty amazing things. Depending on a lot of little details (The devil is hiding here). I found 3Blue1Brown's explanation to be the best, but less "ready to use". ▶ this video

Not to take away the brilliance of what is achieved but I think hologram is the wrong word. This is purely about caustics. Amplitude engineering rather than phase. The calculations are just assuming light as particle, not light as wave. A true hologram uses diffraction grating effects and the phase difference from light. There was a very nice explanation on three-blue-brown recently. ▶ this video I don't think there are any phase effects in the parent attached? Or are there?