One reliable and inexpensive method of doing this is to use a electromechanical shutter, such as those designed and built by nmLaser Products, Sunnyvale, Calif. (nmlaser.com). They rely on an optically coated flexure beam to cover the window and prevent the laser beam from shining through. Energizing the toroidal electromagnet, however, makes it pull the cantilevered beam down, letting 100% of the laser beam pass through. If there is a power failure, the beam returns to the closed position. Beam stresses are so low, the beam's spring life is nearly infinite, according to the company. Simple dc drive circuits or more-sophisticated waveform controllers can control the magnet.
The shutter can modulate at up to 500 Hz and create lasers pulses as short as 800 sec. The design uses few moving parts, so there are no friction pivots, lubricated bearings, or linkages. It is also better suited to high optical power applications than high-speed performance, and it also has a high damage threshold.