Some Copypasta from Wiki for a description.

The rapatronic camera is a high-speed camera capable of recording a still image with an exposure time as brief as 10 nanoseconds (billionths of a second).

The camera was developed by Harold Edgerton in the 1940s and was first used to photograph the rapidly-changing matter in nuclear explosions within milliseconds of ignition. To overcome the speed limitation of a conventional camera\’s mechanical shutter, the rapatronic camera uses two polarizing filters and a Kerr cell. The two filters are mounted with their polarization angles at 90° to each other, to block all incoming light. The Kerr cell between the filters, which changes the polarization of light passing through it when energized, acts as shutter when it is energized at the right time for a very short amount of time, allowing the film to be properly exposed.

For a film-like sequence of high-speed photographs, as used in the photography of nuclear and thermonuclear tests, arrays of up to 12 cameras were deployed, with each camera carefully timed to record a different time frame.