In some applications, it is necessary to chop two beams with the same optical chopper disc. This application note shows how it is possible to vary the phase relationship of the chopping action on the two beams.

The most common requirement is to either chop the two beams at the same time (in phase) or to alternate between the two beams (180° out of phase). The following two diagrams show how this is possible with the 5 slot disc.

Obviously, if you use a disc with an even number of slots, rather than the odd number of slots above, then the phase relationship will be swapped.

Other phase relationships are possible through carefull positioning of the optical beams.