Mass use in 2  <i>μ</i> m laser-driven tin plasma using sheet targets

Abstract

We investigate the mass use of 2 μm wavelength laser-driven tin plasmas as formed from thin tin sheet targets, and identify a key dependence of the conversion efficiency (CE), of converting laser light into useful extreme ultraviolet (EUV) photons, on the tin volume overlapping the laser beam. For plasmas driven under a CE-optimized laser intensity, 85 μm beam diameter and 11 ns pulse duration, an optimum overlap volume is approximately 2×10−15 m3, a number relevant for nanolithography applications. Generating plasma using thicker tin sheets results in excess mass with no increase in CE while using thinner sheets leads to laser burnthrough behavior and decreasing CE. We further show the effect of laser burning through targets of insufficient mass on EUV emission anisotropy and emission surface morphology through observations of time-dependent EUV emission, side-view EUV images, and transmitted laser light.