Optical Properties of Gold in the Nonequilibrium Thermalized Stage

Abstract

Basing on a recent paper and a linear response theory for highly excited systems far from equilibrium the macroscopic dielectric function (MDF) is evaluated for highly excited noble metal layers by means of the density-density Green's function in RPA with a crude consideration of the band structure of the metal. The evaluation of the time evolution of the directly measurable reflectivity and absorption is added. The results of a model calculation for gold are compared with the results of new time-resolved pump-probe-experiments.Auf der Grundlage einer vorangegangenen Arbeit sowie einer linearen Antworttheorie fur hochangeregte Systeme weitab vom Gleichgewicht wird die makroskopische dielektrische Funktion (MDF) mit Hilfe der Dichte-Dichte-Green-Funktion in RPA fur hochangeregte Edelmetallschichten berechnet, wobei die Bandstruktur in grober Naherung berucksichtigt wird. Die Berechnung der zeitlichen Entwicklung des der Messung direkt zuganglichen Reflexionsvermogens und der Absorption wird angeschlossen. Die Resultate einer Modellrechnung fur Gold werden mit Ergebnissentleuerer zeitaufgeloster Pump-Probe-Experimente verglichen.

Nonequilibrium Thermoreflectance Evolution of Laser Irradiated Noble Metals

“…Numerical calculations for gold [2] have shown the ability of the model to describe experimental results.…”

“…For the absolute value of the electric field vector 1 8 1 one obtains in (2). The second term in (5) is neglected because of the slow alteration of the amplitude envelope function in comparison with the fast oscillating carrier frequency.…”

“…The square of the transfer amplitude which is necessary for the differential equation system for T, and TL in [l] can be rewritten in terms of the longitudinal oscillator strength [21], known from [2] We assume dksd being unity which is claimed to be better than setting the momentum matrix element to be a constant [23]. It is consistent with [2] and in correspondence with the estimation of qk = 0.001 eV in [l, 21, because the laser intensities given by experiments [5 to 71 are I 2 1 GW/cm2.…”

“…Starting with first principles in [l] a detailed but simple theory has been given from a macroscopic point of view which describes the evolution of transient Lagrange multipliers in the hydrodynamic stage. When restricting to excitations from d-to s-band states by means of a modern version [15] In [2], the macroscopic dielectric function (MDF) has been evaluated within a linear response theory for highly excited systems far from equilibrium [20]. This results in an extension of the well-known Ehrenreich-Cohen formula [21] for the hydrodynamic nonequilibrium stage of evolution.…”

“…Postulating the d-electrons to be k-independent, which allows us to transform the k-space sum into integration with the simple density of states of the Friedel model [l, 18, 191, a special from for the calculation of the MDF was derived in the Appendix of [2]. Numerical calculations for gold [2] have shown the ability of the model to describe experimental results.…”