Optical chopper

A rotating disc chopper was famously used in 1849 by Hippolyte Fizeau in the first non-astronomical measurement of the speed of light.

Optical choppers, usually rotating disc mechanical shutters, are widely used in science labs in combination with lock-in amplifiers.

[1] The chopper is used to modulate the intensity of a light beam, and a lock-in amplifier is used to improve the signal-to-noise ratio.

As the chopper rotates, it periodically blocks the photocell's view of the target aircraft, creating a series of pulses of output.

Liquid crystal shutter glasses are used in conjunction with a synchronized display screen to create the illusion of a three-dimensional image.