Patent ID: 8829478

Claim:
An EUV light source comprising: a droplet generator producing a stream of target material droplets; a first optical gain medium amplifying light on a first beam path without a seed laser providing a seed laser output to the first beam path, said light on said first beam path having a first linear polarization direction, said first beam path being part of a first optical cavity disposed between a target material irradiation site and a first optics; a second optical gain medium amplifying light on a second beam path without a seed laser providing a seed laser output to the second beam path, said light on said second beam path having a second linear polarization direction orthogonal to said first linear polarization direction, said second beam path being part of a second optical cavity disposed between said target material irradiation site and said first optics; at least one of a first variable attenuator and a second variable attenuator, said first variable attenuator attenuating by way of introducing first variable loss in said light on said first beam path, said second variable attenuator attenuating by way of introducing second variable loss in said light on said second beam path; and a beam combiner combining light from said first beam path and said second beam path for such that said light, after said combining, interacts with a target material droplet at said target material irradiation site to produce EUV light emitting plasma.