Investigation of the role of hot electrons in laser-produced plasma heating via simultaneous measurement of Cu K shell and L shell emissions*

We investigate the heating of solid copper (Cu) targets by the second harmonic (527 nm) of the COMET Nd:Glass laser at  Jupiter Laser Facility (JLF) at an intensity of I~10¹⁹ W/cm². Using a Germanium-220 crystal, high-resolution (E/△E~5300) measurements of Cu Kα (7.9 - 8.6 keV) were obtained, and broadband measurements of 7.5 - 10 keV were achieved with moderate resolution (E/△E~2500) using a Von Hamos spectrometer. A Von Hamos-type L shell spectrometer measured emissions from 0.9 - 2 keV. The estimated Cu Kα conversion efficiency, based on K shell spectra from high-resolution and Von Hamos spectrometer, is order of 10^-6 and increases with Cu thickness, reaching a saturation point after 3 μm thick Cu. The linewidth of Cu Kα₁ emission was found to decrease with increasing Cu thickness. Plasma temperature and density are estimated using simultaneously measured L shell spectra. Together, these measurements from Cu K shell and L shell spectra provide a detailed description of HED plasmas generated by a relativistically-intense laser at 527 nm.