Optical trapping is a really cool fall out of the fact that light can be used to apply forces on objects, albeit really really small forces (around 1E-12 or so Newtons to be precise!)
For really tiny things, like biological cells, this can actually be the biggest force in their little world’s, and by creating a tightly focused laser beam you can actually hold onto them and move them around.
In my masters work at the Adaptive Optics Laboratory, I built a rube-goldberg esq optical trap that used a special deformable mirror and shack hartmann beam phase measurement system to command special phase manipulations to the beam that caused the trap to move and alter it’s stiffness in interesting ways.
The video shows a 10 micron polystyrene sphere trapped in a bath of water, as the controller is fed different commands, it changes the reference positions of the phase measurement. A closed loop controller then generates commands to deform the mirror such that the measurement equal the new reference position, causing the trapped sphere to move.