Probably Sony....Sony is without a doubt the leader in professional filming equipment...at least when it comes to the camera....HD...digital processing...the highest resolution available...latest editing software.
They film it faster and play back at normal speed. For example, if they are shooting at (and I am just making up these numbers) 100 frames per second normally, they play it back at 100 fps. Conversely, they can film something at 200 fps and show it back at 100 fps. It is clear as a bell and appears slower than normal. In the old days, they kept filming at the same speed and just showed it back to us slower than normal. This led to jumpy pictures with gaps in between (picture watching a play in baseball in the 70s and not seeing the tag because it was "between" frames). Now, they film it fast and replay normal to give us the slo-mo effect. It really is not too complicated, but it took us a long time to figure out how to do it!
just a high speed camera and film. i believe that a normal speed camera shoots at 24 frames per second. a high speed camera films at 100 or 120 frames per second and when played at the normal play back speed of 24 frames per second it becomes slow motion.