Patent ID: 8164076

Claim:
An extreme ultraviolet light source apparatus for generating an extreme ultraviolet light by irradiating a target with main pulse laser light after irradiating the target with prepulse laser light, the extreme ultraviolet light source apparatus comprising: a prepulse laser light source configured for generating pre-plasma by irradiating the target with the prepulse laser light, the pre-plasma being generated at a different region from a target region, the target region being on a traveling trajectory of the target, the different region being located on an incident side of the prepulse laser light relative to the target region, a part of the target remaining after the irradiation of the target; a stage configured for adjusting a collector mirror for collecting the prepulse laser light; a CCD camera for imaging a luminescence of the pre-plasma; an image analyzer configured for specifying a luminescence position of the pre-plasma based on an imaging result by the CCD camera; and a focus position controller configured for adjusting a focus position of the prepulse laser light by controlling the stage based on a specifying result by the image analyzer.