Laser wavelength dependence of extreme ultraviolet light and particle emissions from laser-produced lithium plasmas

Maximum extreme ultraviolet (EUV) conversion efficiencies (CEs) of 2.3% and 1.8% were achieved in planar Li targets by using pulsed 2ω and 1ω Nd:YAG laser irradiation, respectively. In a forced recombination scheme, the total CE can be expected to be about 4%. The maximum kinetic energy of the lithium ion debris was found to be less than 1 keV, indicating that mirror damage caused by lithium ion debris is more easily mitigated by using a magnetic field than for tin ions. These results suggest that a Li target is a reasonable candidate for an EUV lithography source.