A design window of laser and plasma parameters required for an extreme ultraviolet (EUV) radiation source for practical application for the next generation of lithography has been introduced. We present a simple analytical model of conversion efficiency from laser energy to radiation energy with a wavelength of 13.5 nm with 2 % bandwidth, by considering power balance of laser produced high-z plasma. We also investigate dependence of the EUV emission from tin and tin-oxide plasmas on laser intensity and wavelength in spherical geometry using the GEKKO XII laser system. It is found that the conversion efficiency into a 2% bandwidth about 13.5 nm has a maximum of a few percent near the laser intensity 10 11 W/cm 2. The efficiency is about the same for 1.053 μm and 0.527 μm laser wavelengths. A scaling law of the conversion efficiency on the laser intensity obtained agrees fairly well with the experimental results. The model also explains many features of the spectrum observed in the experiments.