This research disclosure relates to a radiation source. In particular, it relates to a laser-produced plasma (LPP) radiation source. Such an LPP source may provide radiation to a lithographic apparatus. (Photo)lithography is a process of transferring a paltem to a radiation-sensitive substrate by exposing the substrate to radiation having the pattern. Radiation used in a lithographic apparatus may be extreme ultraviolet (EUV). EUV radiation has a wavelength in the range 4 - 20 nm, for example 13.5 nm. One known source of EUV radiation illuminates fuel droplets with laser radiation provided by a laser. This type of source is known as a laser-produced plasma (LPP) source. Typically, the laser radiation is pulsed. The radiation source is arranged such that the laser radiation is provided in a laser beam which is focussed. The fuel droplets are provided by a fuel droplet generator arranged to deliver fuel droplets such that they are illuminated by the laser radiation at an illumination point and thereby generate EUV radiation.
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