Abstract:The ultrafast electron energy transport is investigated in laser-heated warm dense copper in a high flux regime (2.5 AE 0.7 × 10 13 W=cm 2 absorbed). The dynamics of the electron temperature is retrieved from femtosecond time-resolved x-ray absorption near-edge spectroscopy near the Cu L3 edge. A characteristic time of ∼1 ps is observed for the increase in the average temperature in a 100 nm thick sample. Data are well reproduced by two-temperature hydrodynamic simulations, which support energy transport domin… Show more
“…If the initial state is a solid, the lattice is heated due to electron–phonon energy transfer to a new thermal equilibrium over several (tens to hundreds of) picoseconds. During this evolution, many interesting effects such as the ultrafast electron and non-equilibrium phonon dynamics [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], changes in lattice stability [ 20 , 21 , 22 , 23 , 24 ], phase transitions [ 25 , 26 , 27 , 28 , 29 , 30 ], and non-equilibrium electron–phonon interactions [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ] take place. It should be pointed out that these various physical processes are all driven by electronic excitations.…”
The rate of energy transfer between electrons and phonons is investigated by a first-principles framework for electron temperatures up to Te = 50,000 K while considering the lattice at ground state. Two typical but differently complex metals are investigated: aluminum and copper. In order to reasonably take the electronic excitation effect into account, we adopt finite temperature density functional theory and linear response to determine the electron temperature-dependent Eliashberg function and electron density of states. Of the three branch-dependent electron–phonon coupling strengths, the longitudinal acoustic mode plays a dominant role in the electron–phonon coupling for aluminum for all temperatures considered here, but for copper it only dominates above an electron temperature of Te = 40,000 K. The second moment of the Eliashberg function and the electron phonon coupling constant at room temperature Te=315 K show good agreement with other results. For increasing electron temperatures, we show the limits of the T=0 approximation for the Eliashberg function. Our present work provides a rich perspective on the phonon dynamics and this will help to improve insight into the underlying mechanism of energy flow in ultra-fast laser–metal interaction.
“…If the initial state is a solid, the lattice is heated due to electron–phonon energy transfer to a new thermal equilibrium over several (tens to hundreds of) picoseconds. During this evolution, many interesting effects such as the ultrafast electron and non-equilibrium phonon dynamics [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], changes in lattice stability [ 20 , 21 , 22 , 23 , 24 ], phase transitions [ 25 , 26 , 27 , 28 , 29 , 30 ], and non-equilibrium electron–phonon interactions [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ] take place. It should be pointed out that these various physical processes are all driven by electronic excitations.…”
The rate of energy transfer between electrons and phonons is investigated by a first-principles framework for electron temperatures up to Te = 50,000 K while considering the lattice at ground state. Two typical but differently complex metals are investigated: aluminum and copper. In order to reasonably take the electronic excitation effect into account, we adopt finite temperature density functional theory and linear response to determine the electron temperature-dependent Eliashberg function and electron density of states. Of the three branch-dependent electron–phonon coupling strengths, the longitudinal acoustic mode plays a dominant role in the electron–phonon coupling for aluminum for all temperatures considered here, but for copper it only dominates above an electron temperature of Te = 40,000 K. The second moment of the Eliashberg function and the electron phonon coupling constant at room temperature Te=315 K show good agreement with other results. For increasing electron temperatures, we show the limits of the T=0 approximation for the Eliashberg function. Our present work provides a rich perspective on the phonon dynamics and this will help to improve insight into the underlying mechanism of energy flow in ultra-fast laser–metal interaction.
“…The laser, with an intensity of 1014Wnormalcm−2, heats a copper sample of 100 nm thickness deposited on a PET substrate. (Figure taken from [31]. )Figure 9( a ) Evolution of the electronic temperature as a function of the initial depth and time, for diffusive transport.…”
Section: Time Evolution Of a Femtosecond Laser Heated Copper Foilmentioning
confidence: 99%
“…The laser, with an intensity of 1014Wnormalcm−2, heats a copper sample of 100 nm thickness deposited on a PET substrate. (Figure taken from [31]. )…”
Section: Time Evolution Of a Femtosecond Laser Heated Copper Foilmentioning
Combining experimental set up and
ab initio
molecular dynamics simulations, we were able to follow the time evolution of the X-ray absorption near edge spectrum (XANES) of a dense copper plasma. This provides a deep insight into femtosecond laser interaction with a metallic copper target. This paper presents a review of the experimental developments we made to reduce the X-ray probe duration, from approximately 10 ps to fs duration with table-top laser systems. Moreover, we present microscopic scale simulations, performed with Density Functional Theory, as well as macroscopic simulations considering the Two-Temperature Model. These tools allow us to get a complete picture of the evolution of the target at a microscopic level, from the heating process to the melting and expansion stages, with a clear view of the physics involved during these processes.
This article is part of the theme issue ‘Dynamic and transient processes in warm dense matter’.
The use of laser–plasma-based x-ray sources is discussed, with a view to carrying out time-resolved x-ray absorption spectroscopy measurements, down to the femtosecond timescale. A review of recent experiments performed by our team is presented. They concern the study of the nonequilibrium transition of metals from solid to the warm dense regime, which imposes specific constraints (the sample being destroyed after each shot). Particular attention is paid to the description of experimental devices and methodologies. Two main types of x-ray sources are compared, respectively, based on the emission of a hot plasma, and on the betatron radiation from relativistic electrons accelerated by laser.
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