An extreme ultraviolet light system comprising: a drive laser system that produces an amplified light beam; a guide laser that produces a guide laser beam; a target material delivery system configured to produce a target material at a target location within a vacuum space defined within a chamber, wherein the vacuum chamber houses an extreme ultraviolet light collector (135,935,1035) configured to collect extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material; a beam delivery system including a set of optical components (120,122) and being configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location; a metrology system (124, 360, 460, 960, 1060) comprising: a light collection system configured to collect at least a diagnostic portion of the amplified light beam not reaching the target location and at least a diagnostic portion of the guide laser beam not reaching the target location, the light collection system comprising a dichroic optical device (415, 915, 1015) configured to separate the diagnostic portions by transmitting substantially all of one of the portions and reflecting substantially all of the other of the portions, the at least two diagnostic portions having distinct wavelengths; and an optical sensor that captures the at least two diagnostic portions separated by the dichroic optical device; and a controller connected to the optical sensor and to at least one component within the beam delivery system to modify a position of the at least one component based on the output of the optical sensor. a drive laser system that produces an amplified light beam; a guide laser that produces a guide laser beam; a target material delivery system configured to produce a target material at a target location within a vacuum space defined within a chamber, wherein the vacuum chamber houses an extreme ultraviolet light collector (135,935,1035) configured to collect extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material; a beam delivery system including a set of optical components (120,122) and being configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location; a metrology system (124, 360, 460, 960, 1060) comprising: a light collection system configured to collect at least a diagnostic portion of the amplified light beam not reaching the target location and at least a diagnostic portion of the guide laser beam not reaching the target location, the light collection system comprising a dichroic optical device (415, 915, 1015) configured to separate the diagnostic portions by transmitting substantially all of one of the portions and reflecting substantially all of the other of the portions, the at least two diagnostic portions having distinct wavelengths; and an optical sensor that captures the at least two diagnostic portions separated by the dichroic optical device; and a light collection system configured to collect at least a diagnostic portion of the amplified light beam not reaching the target location and at least a diagnostic portion of the guide laser beam not reaching the target location, the light collection system comprising a dichroic optical device (415, 915, 1015) configured to separate the diagnostic portions by transmitting substantially all of one of the portions and reflecting substantially all of the other of the portions, the at least two diagnostic portions having distinct wavelengths; and an optical sensor that captures the at least two diagnostic portions separated by the dichroic optical device; and a controller connected to the optical sensor and to at least one component within the beam delivery system to modify a position of the at least one component based on the output of the optical sensor.