Dielectric function of warm dense gold

Single-state measurements of the broadband ( 450 - 800 nm ) dielectric function of gold using a supercontinuum probe are reviewed. These measurements have demonstrated the first evidence of the existence of band structure in ultrathin gold foils isochorically heated by a femtosecond laser pulse to energy densities of 10 6 - 10 7 J ∕ kg . The Drude component of the dielectric function increases with energy density while the interband component shows both enhancement and redshift. Ab initio molecular-dynamics calculations based on thermalized electrons cannot reproduce the experimental results, suggesting a non-Fermi distribution of excited electrons.