A high-speed two-bladed shutter was built to deliver square-wave pulses of energy from a converging light beam with an average intensity of about 5 cal/cm 2 /sec, and a diameter of 3 in., in the plane of the shutter. The blades open or close in less than 0.01 sec. They move in the same direction, so that all parts of the target are exposed for very nearly the same length of time. The shutter makes use of a new type of air cylinder which is suitable for driving high-speed mechanisms, and has a dynamic shock absorbing system to stop the moving parts in a short distance with little rebound. It is electrically controlled and fully automatic. Exposure times may be varied from 0.07 to 5 sec by setting an electronic interval timer. Longer exposures are controlled manually. To date it has been used more than 15000 times and has required only two overhauls.