Cylindrically and non-cylindrically symmetric expansion dynamics of tin microdroplets after ultrashort laser pulse impact

Tiago De Faria Pinto,Oscar O Versolato,Alex Bayerle,Hao Zhang,Kjeld S E Eikema,Randy Meijer,Dmitry Kurilovich,Stefan Witte,Jan Mathijssen

doi:10.1007/s00339-020-04207-9

Abstract

In this work, the expansion dynamics of liquid tin micro-droplets irradiated by femtosecond laser pulses were investigated. The effects of laser pulse duration, energy, and polarization on ablation, cavitation, and spallation dynamics were studied using laser pulse durations ranging from 220 fs to 10 ps, with energies ranging from 1 to 5 mJ, for micro-droplets with an initial radius of 15 and 23 upmum. Using linearly polarized laser pulses, cylindrically asymmetric shock waves were produced, leading to novel non-symmetric target shapes, the asymmetry of which was studied as a function of laser pulse parameters and droplet size. A good qualitative agreement was obtained between smoothed-particle hydrodynamics simulations and high-resolution stroboscopic experimental data of the droplet deformation dynamics.

Highlights

The current generation of nanolithography machines uses extreme ultraviolet (EUV) light to enable the printing of ever smaller features
Each of these processes leads to Cylindrically and non-cylindrically symmetric expansion dynamics of tin microdroplets after
The effects of pulse energy and duration on the shockwave-driven expansion dynamics of liquid tin microdroplets irradiated by ultrashort laser pulses have been reported in this work

Summary

Introduction

The current generation of nanolithography machines uses extreme ultraviolet (EUV) light to enable the printing of ever smaller features. To generate EUV radiation, a laserproduced plasma (LPP) is created by focusing high-energy laser pulses onto liquid micro-droplets of tin, where line emission from highly charged ions in the plasma produces the desired 13.5 nm light [1,2,3,4,5,6]. Some such laser pulses induce strong shock waves on the metal droplets, causing them to deform hydrodynamically and, for the most intense pulses, undergo explosive cavitation [7,8,9,10]. Recent evidence suggests that a droplet fragmented into a cloud of small particles, as one can obtain when using ps pulses, could be a favourable target for EUV generation [14, 15]

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Conclusion