Extreme ultraviolet light source apparatus

An extreme ultraviolet light source apparatus for generating extreme ultraviolet light by irradiating a target material with a laser beam to turn the target material into plasma, said apparatus comprising:

• a chamber in which the extreme ultraviolet light is generated;
• a target supply mechanism for supplying the target material into said chamber;
• a driver laser for irradiating the target material, which is supplied by said target supply mechanism, with the laser beam to generate the plasma;
• a collector mirror having a first focal point and a second focal point, for reflecting light, which is generated at said first focal point, toward said second focal point;
• a splitter optical element for focusing the extreme ultraviolet light having a predetermined wavelength, which has been reflected by said collector mirror and passed through said second focal point, on a third focal point, and for splitting light having other wavelengths which has been reflected by said collector mirror and passed through said second focal point;
• and
• a detection mechanism provided in an optical path of the light split by said splitter optical element, for detecting a profile of the light split by said splitter optical element.