Laser-to-droplet alignment sensitivity relevant for laser-produced plasma sources of extreme ultraviolet light

Abstract

We present and experimentally validate a model describing the sensitivity of the tilt angle, expansion, and the propulsion velocity of a tin micro-droplet irradiated by a 1 μm Nd:YAG laser pulse to its relative alignment. This sensitivity is particularly relevant in industrial plasma sources of extreme ultraviolet light for nanolithographic applications. Our model has but a single parameter: the dimensionless ratio of the laser spot size to the effective size of the droplet, which is related to the position of the plasma critical density surface. Our model enables the development of straightforward scaling arguments, in turn enabling precise control of the alignment sensitivity.