Characterization of angularly resolved EUV emission from 2-µm-wavelength laser-driven Sn plasmas using preformed liquid disk targets

Publication date
DOI http://dx.doi.org/10.1088/1361-6463/ac0b70
Reference R. Schupp, L. Behnke, Z. Bouza, Z. Mazzotta, Y. Mostafa, A. Lassise, L. Poirier, J. Sheil, M. Bayraktar, W.M.G. Ubachs, R. Hoekstra and O.O. Versolato, Characterization of angularly resolved EUV emission from 2-µm-wavelength laser-driven Sn plasmas using preformed liquid disk targets, J. Phys. D: Appl. Phys. 54, 36: 365103: 1-12 (2021)
Group EUV Plasma Processes

The emission properties of tin plasmas, produced by the irradiation of preformed liquid tin targets by several-ns-long 2-μm-wavelength laser pulses, are studied in the extreme ultraviolet (EUV) regime. In a two-pulse scheme, a pre-pulse laser is first used to deform tin microdroplets into thin, extended disks before the main (2μm) pulse creates the EUV-emitting plasma. Irradiating 30- to 300-μm-diameter targets with 2-μm laser pulses, we find that the efficiency in creating EUV light around 13.5nm follows the fraction of laser light that overlaps with the target. Next, the effects of a change in 2-μm drive laser intensity (0.6–1.8×1011W/cm2) and pulse duration (3.7–7.4ns) are studied. It is found that the angular dependence of the emission of light within a 2% bandwidth around 13.5nm and within the backward 2π hemisphere around the incoming laser beam is almost independent of intensity and duration of the 2-μm drive laser. With increasing target diameter, the emission in this 2% bandwidth becomes increasingly anisotropic, with a greater fraction of light being emitted into the hemisphere of the incoming laser beam. For direct comparison, a similar set of experiments is performed with a 1-μm-wavelength drive laser. Emission spectra, recorded in a 5.5–25.5nm wavelength range, show significant self-absorption of light around 13.5nm in the 1-μm case, while in the 2-μm case only an opacity-related broadening of the spectral feature at 13.5nm is observed. This work demonstrates the enhanced capabilities and performance of 2-μm-driven plasmas produced from disk targets when compared to 1-μm-driven plasmas, providing strong motivation for the use of 2-μm lasers as drive lasers in future high-power sources of EUV light.