Patent ID: 7372056

Claim:
An EUV light generation system comprising: a droplet generator producing plasma source material target droplets traveling toward the vicinity of a plasma source material target irradiation site wherein each respective droplet has 200 to 400 μm separation; a drive laser; a drive laser focusing optical element having a first range of operating center wavelengths; a droplet detection radiation source having a second range of operating center wavelengths; a drive laser steering element comprising a material that is highly reflective within at least some part of the first range of wavelengths and highly transmissive within at least some part of the second range of center wavelengths; a droplet detection radiation aiming mechanism directing the droplet detection radiation through the drive laser steering element and the lens to focus at a selected droplet detection position intermediate the droplet generator and the irradiation site; and a droplet detection mechanism comprising a droplet detection radiation detector positioned to detect droplet detection radiation reflected from a plurality of plasma source material droplets.