Time-resolved observation of electron-phonon relaxation in copper.
TL;DR: In this paper, the process of electron-phonon energy transfer was time resolved and was observed to be 1--4 ps increasing with the laser fluence, and non-equilibrium electron-lattice temperatures were observed.
Abstract: Amplified 150--300-fs laser pulses are applied to monitor the thermal modulation of the transmissivity of thin copper films. Non- equilibrium electron-lattice temperatures are observed. The process of electron-phonon energy transfer was time resolved and was observed to be 1--4 ps increasing with the laser fluence.
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TL;DR: In this article, a universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion, wave, phonon-electron interactions, and pure phonon scattering.
Abstract: A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon-electron interactions (microscopic in both space and time), and pure phonon scattering The model is generalized from the dual-phase-lag concept accounting for the laging behavior in the high-rate response While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon-electron interaction)
1,435 citations
TL;DR: In this article, the dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature was investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti.
Abstract: The dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature is investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti, for the conditions of strong electron-phonon nonequilibrium. These conditions are characteristic of metal targets subjected to energetic ion bombardment or short-pulse laser irradiation. Computational analysis based on first-principles electronic structure calculations of the electron density of states predicts large deviations (up to an order of magnitude) from the commonly used approximations of linear temperature dependence of the electron heat capacity and a constant electron-phonon coupling. These thermophysical properties are found to be very sensitive to details of the electronic structure of the material. The strength of the electron-phonon coupling can either increase (Al, Au, Ag, Cu, and W), decrease (Ni and Pt), or exhibit nonmonotonic changes (Ti) with increasing electron temperature. The electron heat capacity can exhibit either positive (Au, Ag, Cu, and W) or negative (Ni and Pt) deviations from the linear temperature dependence. The large variations of the thermophysical properties, revealed in this work for the range of electron temperatures typically realized in femtosecond laser material processing applications, have important implications for quantitative computational analysis of ultrafast processes associated with laser interaction with metals.
1,165 citations
TL;DR: In this paper, the authors studied the ablation of metal targets by Ti:sapphire laser radiation and showed that the intensity depends logarithmically on the laser fluence.
Abstract: Ablation of metal targets by Ti:sapphire laser radiation is studied. The ablation depth per pulse is measured for laser pulse durations between 150 fs and 30 ps and fluences ranging from the ablation threshold ∼0.1 J/cm2 up to 10 J/cm2. Two different ablation regimes are observed for the first time. In both cases the ablation depth per pulse depends logarithmically on the laser fluence. A simple theoretical model for a qualitative description of the experimental results is presented.
914 citations
TL;DR: Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts.
Abstract: Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...
892 citations
TL;DR: In this article, a pump-pump-probe technique was introduced which allows to study hot electron relaxation by probing the reflectivity in thermal equilibrium between electrons and lattice.
842 citations