The wheel is driven by a small electric motor.Īs shown in Figure 1, there can be two (and rarely more) rows of slits, often with different numbers of holes, so that different chopping frequencies can be achieved with a given rotation frequency. Its central part is a chopper disc (also called chopper blade) which is typically made of a black coated metal, having the shape of a circle with some pattern of holes or slits (slots). The most common form of optical chopper is that of a rotating disc chopper. Rotating Disc Choppers Figure 1: A chopper wheel with two rows of holes. Besides, they may produce disturbing mechanical vibrations of an optical setup. On the other hand, mechanical choppers are limited in frequency and switching speed, and they output partially truncated beams during the switching. Also, simple mechanical choppers can be far cheaper than electronically controlled modulators. This is in contrast to the use of various kinds of intensity modulators, which may exhibit incomplete transmission, beam distortions, effects of nonlinearities etc. The simple mechanical operation principle – letting a beam pass or block it with some blade – makes such devices work for basically any optical wavelength, and beam distortions in the open state are avoided. See below for some examples of applications.

Usually, they are used for periodically modulating the optical power of a beam. There are different kinds of optical chopper devices which can be used for periodically transmitting and interrupting a light beam – for example, a laser beam – with mechanical means.

High frequency tuning fork