Patent ID: 8785893

Claim:
An extreme ultraviolet light source apparatus comprising: an extreme ultraviolet light source; a light focusing optical means, which reflects and focuses light emitted from the light source; a light focusing optical means moving unit, which moves the light focusing optical means; an Angular distribution property measurement unit, which receives light reflected by the light focusing optical means, and which obtains Angular distribution property image data; which is image data indicating a direction of shift from an alignment position of the light focusing optical means, and an amount thereof, as a degree of unevenness of illuminance distribution, a control unit, which controls the light focusing optical means moving unit based on the Angular distribution property image data, so as to move the light focusing optical means, wherein the control unit includes: a memory unit for storing two or more pieces of Angular distribution property image data in which illuminance distribution measured in advance is uneven, and a movement direction and an amount of movement, which are associated with the Angular distribution property image data, and which are used to move a position of the light focusing optical means when Angular distribution property image data indicating uneven illuminance distribution is obtained, to a position where Angular distribution property image data indicating uniform illuminance is obtained, a comparison and selection unit, which: compares current Angular distribution property image data measured by the Angular distribution property measurement unit with Angular distribution property image data saved in the memory unit in which illuminance is uneven, selects Angular distribution property image data that is the most closely matched in a shape of an Angular distribution property to the current Angular distribution property image data, from two or more pieces of the saved Angular distribution property image data, and reads out the saved movement direction and amount of movement of the light focusing optical means that are associated with the selected Angular distribution property image data, and a light focusing optical means movement control unit which controls the light focusing optical means moving unit so as to move the light focusing optical means based on the saved movement direction and amount of movement of the light focusing optical means that are associated with the Angular distribution property image data read out by the comparison selection unit.