Filtering of a source of pulsed radiation

A source of pulsed radiation is coupled to a positionable filter. The positionable filter includes an element that produces an indication of a position of the filter. The source is configured to receive the indication of the position of the filter, and to regulate emission of a pulse of radiation based on the indication. A device includes an area including a material that alters a parameter of a beam of radiation that interacts with the material. The device is configured to move relative to a source of pulsed radiation. An element provides a signal to the source of pulsed radiation that indicates a position of the area relative to the source. The signal causes the source to trigger emission of a pulse at a time such that the emitted pulse is incident upon a portion of the area.