Abstract

The cooling dynamics of electrons excited near a solid surface have attracted substantial interest since the invention of ultrafast sources. For relatively low electron-excitation levels (T_e < 1500 K, but more typically <400 K) the most common probes of hot-electron dynamics have been measurements of various transient thermo-optical properties.¹ These optical techniques have not been extended into higher excitation regimes, in part because the lower repetition rates of high-intensity laser pulses make it more difficult to precisely measure minute changes in optical response. However, recent work, which has quantified space-charge-limited ultrafast thermionic emission,² provides a basis for the investigation of electron cooling for peak electron temperatures T_peak above ~ 2500 K. Here we report on two-pulse correlation thermionic-emission measurements obtained on a 5000-Å thick polycrystalline Au film. The results demonstrate the need to account for the temperature dependence of the electron-phonon coupling parameter G and the thermal conductivity κ at these higher excitation levels. When these temperature dependencies are taken into account, excellent quantitative agreement between calculated and measured peak-electron temperatures and electron cooling rates is achieved.

© 1994 Optical Society of America