Laser Thomson Scattering Measurements of Electron Properties in Nanosecond Pulsed Laser-Produced Plasmas using Gas and Solid Targets

Understanding the properties of electrons and ions in nanosecond pulsed laser-produced plasmas (LPPs) is crucial for elucidating the fundamental mechanisms and scaling laws that govern their efficiency across a broad range of applications. These applications include gas-phase nanoparticle synthesis, trace material detection, ignition of combustible mixtures, and extreme ultraviolet (EUV) light sources for lithography. We present a comparative study of the electron properties in laser-produced plasmas generated in two different environments: (a) in gases (argon and argon with 3% water vapor, both at atmospheric pressure) and (b) by ablating a solid tin wire in a low-pressure argon gas background. To meet the specific requirements of EUV lithography, all LPPs were produced using the 1064 nm fundamental output of a Nd:YAG laser with a typical intensity of 10¹¹ W/cm² at the focal spot. Time-resolved laser Thomson scattering (LTS) measurements in the gaseous targets revealed similar results, with peak electron number densities exceeding 10¹⁷ cm^-3 early in time, followed by a decrease by an order of magnitude within 20 µs. The electron temperature dynamics were also comparable, with a peak temperature of 7 eV that decreased to approximately 1 eV after 20 µs. Both collective and non-collective LTS regimes were observed.