Method and device for monitoring multiple mirror arrays in an illumination system of a microlithographic projection exposure apparatus

A system, comprising:

• a multi-mirror array (MMA) comprising a plurality of movable mirror elements;
• a device for monitoring the moveable mirror elements of the MMA, wherein the monitoring device comprises:
• a detector;
• and
• at least one lens that is arranged to direct light reflected from moveable mirror elements of the MMA to the detector,
• wherein the at least one lens has a focal plane in which the detector is arranged, and
• the system is an illumination system of a microlithographic apparatus,
• wherein the at least one lens is one of an array of lenses each focusing light to a common focal plane,
• the system further comprising at least one additional lens between the array of lenses and the MMA, the at least one additional lens being configured to direct light from the MMA to the lens array, and
• wherein the detector and at least one additional lens are arranged to satisfy the Scheimpflug condition with respect to a plane of the MMA.

A method of operating an illumination system of a microlithographic apparatus comprising a multi-mirror array (MMA), the method comprising:

• directing light to reflect from at least one moveable mirror element of the MMA;
• focusing the reflected light onto a detector using at least one lens, the detector being arranged in a focal plane of the at least one lens;
• monitoring an alignment of the at least one moveable mirror element based on a signal from the detector in response to the reflected light;
• and
• wherein the at least one lens and the detector are arranged relative to the MMA so that a position of light reflected from a moveable mirror element of the MMA at the detector corresponds to a tilt angle of the moveable mirror element.