Abstract: A radiation source for generating EUV radiation includes a laser configured to fire laser pulses at a target area to which is supplied a stream of fuel droplets, which may be tin droplets that emit EUV radiation when excited by the laser beam. The EUV radiation is collected by a collector. The tin droplets may be pre-conditioned by a laser pre-pulse before the main laser pulse to change the shape of the droplets so that the droplets are in an optimum condition for receiving the main laser pulse. Embodiments of the invention take into account the effect of the vaporization of one fuel droplet on succeeding droplets and allow the timing of the main and/or pre-pulse to be adjusted to take into account any delay in arrival of the subsequent droplet or oscillations in the shape of the subsequent droplet which may be caused by vaporization of the preceding droplet.

Abstract: A radiation source having a fuel stream generator (110) that generates and directs a fuel stream (102) along a trajectory towards a plasma formation location (104). A pre-pulse laser radiation assembly directs a first beam of laser radiation (100) at the fuel stream at the plasma formation location to generate a modified fuel target (106). A main pulse laser radiation assembly directs a second beam of laser radiation (108) at the modified fuel target at the plasma formation location to generate a radiation generating plasma (117). A collector (122) collects the radiation and directs it along an optical axis (105) of the radiation source. The first beam of laser radiation being directed toward the fuel stream substantially along the optical axis.

Abstract: A radiation source for generating EUV radiation includes a laser configured to fire laser pulses at a target area to which is supplied a stream of fuel droplets, which may be tin droplets that emit EUV radiation when excited by the laser beam. The EUV radiation is collected by a collector. The tin droplets may be pre-conditioned by a laser pre-pulse before the main laser pulse to change the shape of the droplets so that the droplets are in an optimum condition for receiving the main laser pulse. Embodiments of the invention take into account the effect of the vaporization of one fuel droplet on succeeding droplets and allow the timing of the main and/or pre-pulse to be adjusted to take into account any delay in arrival of the subsequent droplet or oscillations in the shape of the subsequent droplet which may be caused by vaporization of the preceding droplet.