Patent ID: 8604453

Claim:
An extreme ultraviolet light source apparatus, which is to generate an extreme ultraviolet light by irradiating a target with a main pulse laser light after irradiating the target with a prepulse laser light, the extreme ultraviolet light source apparatus comprising: a prepulse laser light source configured for generating a pre-plasma by irradiating the target with the prepulse laser light while a part of the target remains; a main pulse laser light source configured for generating the extreme ultraviolet light by irradiating the pre-plasma with the main pulse laser light; a light source configured for illuminating the pre-plasma generated by irradiating the target with the prepulse laser light; a camera configured for imaging the pre-plasma illuminated by the light source; an analyzer configured for analyzing an image of the pre-plasma imaged by the camera; and a controller configured for controlling a focus position of the main pulse laser light based on an analysis of the analyzer.