The simplest shutter is made from opaque material that does not transmit electromagnetic radiation through when it is closed.

When this shutter is out of the beam path (“open” state), it does nor disturb the transmission of the beam.

A simple method for creating a relatively fast shutter is by a spinning wheel with a hole off center, as described in figure 7.21.

The wheel with the hole is inside the optical cavity, between the active medium and the mirror.

during its spinning, the hole arrive in line with the optic axis of the laser, it enable lasing process.

The problem with this shutter is slow switching speed, dictated by mechanical motion. Thus, the switching time from one state to the other is at least 1 [msec].

The switching time is the time in which the switch is neither in “close” position, nor in “open” position.

When using spinning wheel, the transition to lasing state starts when part of the hole is in line with the active medium.