Ok, Not electronic in nature....BUT STILLLL!

Ok, ok this isnt electronic in nature, but I need some smart cookies brains anyways. I recently watched a video somewhere (OR maybe it was on TV???). Where someone was using slit-screens being rotated in such a matter that they could stop a light beam (only looking like it was, not actually stopping light).
Somehow he modulated several light beams and he could make a short pulse look as tho it was going, fast or slow, or stopping altogether.
Did anyone see this ?...I have looked everywhere...googled my fingers off, and I cant find it.
Please help

That sounds like a stroboscopic effect?

Tom Scott on YouTube.

HOLY Crap...you found what I couldnt!!...what type of laser/ optics system is he using????

I regularly watch Tom's videos. Very interesting stuff.