Thermomodulation Spectra of Al, Au, and Cu

Abstract

Thermotransmission and thermoreflection measurements were made on semitransparent films of Al, Au, and Cu at about 370 and 120 K in the range 0.5-5 eV. The data yield the thermomodulation spectrum Δε2 of the imaginary part of the dielectric constant directly, without Kramers-Kronig analysis. A comparison of the interband region of Δε2 for Cu with the piezo-modulation spectrum of a single crystal shows that broadening of the Fermi distribution and volume strain caused by thermal expansion are the principal causes of the Δε2 spectrum. The Δε2 spectrum for Al is particularly simple and can be discussed using closed-form expressions for the optical conductivity. It appears that the temperature dependence of the interband relaxation time for transitions across gaps produced by |V111| is smaller than that for transitions across gaps caused by |V200|, which in turn is smaller than that for the infrared intraband transitions.

Gold nanoparticle assemblies: interplay between thermal effects and optical response

“…The origins of the thermo-optical response of noble metals are multiple and were the subject of numerous investigations in the 1970s, particularly for gold [24,27,[98][99][100][101]. Various mechanisms lead to the modification of the interband and intraband transitions following a temperature variation, by affecting either directly the electron distribution, or the properties related to the lattice via the increase of the interatomic distance, or the collision processes.…”

“…In gold, the points X (onset at ~1.9 eV [17,27]) and especially L (onset at ~2.4 eV [27]) of the BZ provide the main contributions to d→sp interband transitions in the visible. Around these two points the ( ) d sp M → k can be considered as locally constant, since the wave number range matching the energy conservation condition is very narrow [24,27]. Thus, for a transition around X or L , 2 ib ε is proportional to the joint density of states (i.e.…”

“…Thus, for a transition around X or L , 2 ib ε is proportional to the joint density of states (i.e. associated with a transition of given energy) which is linked with the densities of states in the d and sp bands and accounts for the energy and wave vector conservation [24]:…”

Spectroscopic study of optically induced ultrafast electron dynamics in gold

“…12 However, such an assumption ͑referred to as the "linearity assumption" from hereon͒ is not self-consistent since transient reflectivity and transmission signals appear to have a different temporal shape, [13][14][15][16][17][18] and hence cannot be both proportional to the same function of time, e.g., the transient electron temperature. As has been known since the early optical thermomodulation studies of metals, 19 rigorous analysis instead requires the transient reflectivity and transmission to be properly calculated from the dependence of the complex dielectric function upon the electron occupation number. In practice, the full calculation was normally used only for simulation, while simplified analytical "response functions" were used to fit the data, thus implicitly making the unjustified assumption of linearity ͑see for example Refs.…”

“…Due to its well-known optical properties, 19,24 gold has been the metal most widely studied in optical pump-probe measurements. A correct understanding of its transient reflectivity provides a basis for the understanding and quantification of experiments on other metals.…”