We investigate the spatial and temporal dynamics of plasma formed on liquid tin sheets when irradiated with a 5 ns laser pulse at an intensity I of several 108 W/cm2. From temporally integrated images of plasma emission, we deduce that there must be an intensity-specific minimum thickness at which plasma formation still occurs. Time-resolved detection of the laser light transmitted through and along the sheet reveals fast dynamics in the competition between vaporization and plasma formation. The overall dynamics are well captured in models that combine preexisting scaling laws for the time to full vaporization (∼I−1) and the time to plasma onset (∼I−2). These findings are particularly relevant for target preparation and metrology in plasma light sources utilizing tin targets to produce extreme ultraviolet light for nanolithography applications, including metrology.
Schubert et al. (Thu,) studied this question.