Two Diffraction Gratings - Rotation

[Hunter235711]

Can someone explain how the laser pointer is generating the rectangular patterns shown in this youtube video?

I assume that there are just two diffraction gratings that are rotated relative to each other, but could someone explain mathematically how to predict what pattern is formed for different rotation angles?

Thanks,
Hunter

 

[DarkBabylon]

Think the image I handcrafted hastely attached could explain it.
Believe there are two diffraction grating layers, and for the 90 degree rotation from one another, you'd see the light splitting at first into 3 rays diverging, and each ray of that splits again at the second diffraction grating layer, into 3, this time vertically instead of horizontally.
The diffraction gratings in the image are of a single axis, that video shows a double axis diffraction.

There could also be polarization to be taken into account, though. Frankly I don't know how the laser in the video was built.